Bug Summary

File:lib/Transforms/Scalar/LICM.cpp
Warning:line 1092, column 7
Called C++ object pointer is null

Annotated Source Code

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clang -cc1 -triple x86_64-pc-linux-gnu -analyze -disable-free -disable-llvm-verifier -discard-value-names -main-file-name LICM.cpp -analyzer-store=region -analyzer-opt-analyze-nested-blocks -analyzer-eagerly-assume -analyzer-checker=core -analyzer-checker=apiModeling -analyzer-checker=unix -analyzer-checker=deadcode -analyzer-checker=cplusplus -analyzer-checker=security.insecureAPI.UncheckedReturn -analyzer-checker=security.insecureAPI.getpw -analyzer-checker=security.insecureAPI.gets -analyzer-checker=security.insecureAPI.mktemp -analyzer-checker=security.insecureAPI.mkstemp -analyzer-checker=security.insecureAPI.vfork -analyzer-checker=nullability.NullPassedToNonnull -analyzer-checker=nullability.NullReturnedFromNonnull -analyzer-output plist -w -mrelocation-model pic -pic-level 2 -mthread-model posix -fmath-errno -masm-verbose -mconstructor-aliases -munwind-tables -fuse-init-array -target-cpu x86-64 -dwarf-column-info -debugger-tuning=gdb -momit-leaf-frame-pointer -ffunction-sections -fdata-sections -resource-dir /usr/lib/llvm-7/lib/clang/7.0.0 -D _DEBUG -D _GNU_SOURCE -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D __STDC_LIMIT_MACROS -I /build/llvm-toolchain-snapshot-7~svn337490/build-llvm/lib/Transforms/Scalar -I /build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar -I /build/llvm-toolchain-snapshot-7~svn337490/build-llvm/include -I /build/llvm-toolchain-snapshot-7~svn337490/include -U NDEBUG -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/x86_64-linux-gnu/c++/8 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/x86_64-linux-gnu/c++/8 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/8/../../../../include/c++/8/backward -internal-isystem /usr/include/clang/7.0.0/include/ -internal-isystem /usr/local/include -internal-isystem /usr/lib/llvm-7/lib/clang/7.0.0/include -internal-externc-isystem /usr/lib/gcc/x86_64-linux-gnu/8/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -O2 -Wno-unused-parameter -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -Wno-maybe-uninitialized -Wno-comment -std=c++11 -fdeprecated-macro -fdebug-compilation-dir /build/llvm-toolchain-snapshot-7~svn337490/build-llvm/lib/Transforms/Scalar -ferror-limit 19 -fmessage-length 0 -fvisibility-inlines-hidden -fobjc-runtime=gcc -fdiagnostics-show-option -vectorize-loops -vectorize-slp -analyzer-output=html -analyzer-config stable-report-filename=true -o /tmp/scan-build-2018-07-20-043646-20380-1 -x c++ /build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp -faddrsig
1//===-- LICM.cpp - Loop Invariant Code Motion Pass ------------------------===//
2//
3// The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This pass performs loop invariant code motion, attempting to remove as much
11// code from the body of a loop as possible. It does this by either hoisting
12// code into the preheader block, or by sinking code to the exit blocks if it is
13// safe. This pass also promotes must-aliased memory locations in the loop to
14// live in registers, thus hoisting and sinking "invariant" loads and stores.
15//
16// This pass uses alias analysis for two purposes:
17//
18// 1. Moving loop invariant loads and calls out of loops. If we can determine
19// that a load or call inside of a loop never aliases anything stored to,
20// we can hoist it or sink it like any other instruction.
21// 2. Scalar Promotion of Memory - If there is a store instruction inside of
22// the loop, we try to move the store to happen AFTER the loop instead of
23// inside of the loop. This can only happen if a few conditions are true:
24// A. The pointer stored through is loop invariant
25// B. There are no stores or loads in the loop which _may_ alias the
26// pointer. There are no calls in the loop which mod/ref the pointer.
27// If these conditions are true, we can promote the loads and stores in the
28// loop of the pointer to use a temporary alloca'd variable. We then use
29// the SSAUpdater to construct the appropriate SSA form for the value.
30//
31//===----------------------------------------------------------------------===//
32
33#include "llvm/Transforms/Scalar/LICM.h"
34#include "llvm/ADT/Statistic.h"
35#include "llvm/Analysis/AliasAnalysis.h"
36#include "llvm/Analysis/AliasSetTracker.h"
37#include "llvm/Analysis/BasicAliasAnalysis.h"
38#include "llvm/Analysis/CaptureTracking.h"
39#include "llvm/Analysis/ConstantFolding.h"
40#include "llvm/Analysis/GlobalsModRef.h"
41#include "llvm/Analysis/Loads.h"
42#include "llvm/Analysis/LoopInfo.h"
43#include "llvm/Analysis/LoopPass.h"
44#include "llvm/Analysis/MemoryBuiltins.h"
45#include "llvm/Analysis/MemorySSA.h"
46#include "llvm/Analysis/OptimizationRemarkEmitter.h"
47#include "llvm/Analysis/ScalarEvolution.h"
48#include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
49#include "llvm/Analysis/TargetLibraryInfo.h"
50#include "llvm/Transforms/Utils/Local.h"
51#include "llvm/Analysis/ValueTracking.h"
52#include "llvm/IR/CFG.h"
53#include "llvm/IR/Constants.h"
54#include "llvm/IR/DataLayout.h"
55#include "llvm/IR/DerivedTypes.h"
56#include "llvm/IR/Dominators.h"
57#include "llvm/IR/Instructions.h"
58#include "llvm/IR/IntrinsicInst.h"
59#include "llvm/IR/LLVMContext.h"
60#include "llvm/IR/Metadata.h"
61#include "llvm/IR/PredIteratorCache.h"
62#include "llvm/Support/CommandLine.h"
63#include "llvm/Support/Debug.h"
64#include "llvm/Support/raw_ostream.h"
65#include "llvm/Transforms/Scalar.h"
66#include "llvm/Transforms/Scalar/LoopPassManager.h"
67#include "llvm/Transforms/Utils/BasicBlockUtils.h"
68#include "llvm/Transforms/Utils/LoopUtils.h"
69#include "llvm/Transforms/Utils/SSAUpdater.h"
70#include <algorithm>
71#include <utility>
72using namespace llvm;
73
74#define DEBUG_TYPE"licm" "licm"
75
76STATISTIC(NumSunk, "Number of instructions sunk out of loop")static llvm::Statistic NumSunk = {"licm", "NumSunk", "Number of instructions sunk out of loop"
, {0}, {false}}
;
77STATISTIC(NumHoisted, "Number of instructions hoisted out of loop")static llvm::Statistic NumHoisted = {"licm", "NumHoisted", "Number of instructions hoisted out of loop"
, {0}, {false}}
;
78STATISTIC(NumMovedLoads, "Number of load insts hoisted or sunk")static llvm::Statistic NumMovedLoads = {"licm", "NumMovedLoads"
, "Number of load insts hoisted or sunk", {0}, {false}}
;
79STATISTIC(NumMovedCalls, "Number of call insts hoisted or sunk")static llvm::Statistic NumMovedCalls = {"licm", "NumMovedCalls"
, "Number of call insts hoisted or sunk", {0}, {false}}
;
80STATISTIC(NumPromoted, "Number of memory locations promoted to registers")static llvm::Statistic NumPromoted = {"licm", "NumPromoted", "Number of memory locations promoted to registers"
, {0}, {false}}
;
81
82/// Memory promotion is enabled by default.
83static cl::opt<bool>
84 DisablePromotion("disable-licm-promotion", cl::Hidden, cl::init(false),
85 cl::desc("Disable memory promotion in LICM pass"));
86
87static cl::opt<uint32_t> MaxNumUsesTraversed(
88 "licm-max-num-uses-traversed", cl::Hidden, cl::init(8),
89 cl::desc("Max num uses visited for identifying load "
90 "invariance in loop using invariant start (default = 8)"));
91
92static bool inSubLoop(BasicBlock *BB, Loop *CurLoop, LoopInfo *LI);
93static bool isNotUsedOrFreeInLoop(const Instruction &I, const Loop *CurLoop,
94 const LoopSafetyInfo *SafetyInfo,
95 TargetTransformInfo *TTI, bool &FreeInLoop);
96static bool hoist(Instruction &I, const DominatorTree *DT, const Loop *CurLoop,
97 const LoopSafetyInfo *SafetyInfo,
98 OptimizationRemarkEmitter *ORE);
99static bool sink(Instruction &I, LoopInfo *LI, DominatorTree *DT,
100 const Loop *CurLoop, LoopSafetyInfo *SafetyInfo,
101 OptimizationRemarkEmitter *ORE, bool FreeInLoop);
102static bool isSafeToExecuteUnconditionally(Instruction &Inst,
103 const DominatorTree *DT,
104 const Loop *CurLoop,
105 const LoopSafetyInfo *SafetyInfo,
106 OptimizationRemarkEmitter *ORE,
107 const Instruction *CtxI = nullptr);
108static bool pointerInvalidatedByLoop(Value *V, uint64_t Size,
109 const AAMDNodes &AAInfo,
110 AliasSetTracker *CurAST);
111static Instruction *
112CloneInstructionInExitBlock(Instruction &I, BasicBlock &ExitBlock, PHINode &PN,
113 const LoopInfo *LI,
114 const LoopSafetyInfo *SafetyInfo);
115
116namespace {
117struct LoopInvariantCodeMotion {
118 bool runOnLoop(Loop *L, AliasAnalysis *AA, LoopInfo *LI, DominatorTree *DT,
119 TargetLibraryInfo *TLI, TargetTransformInfo *TTI,
120 ScalarEvolution *SE, MemorySSA *MSSA,
121 OptimizationRemarkEmitter *ORE, bool DeleteAST);
122
123 DenseMap<Loop *, AliasSetTracker *> &getLoopToAliasSetMap() {
124 return LoopToAliasSetMap;
125 }
126
127private:
128 DenseMap<Loop *, AliasSetTracker *> LoopToAliasSetMap;
129
130 AliasSetTracker *collectAliasInfoForLoop(Loop *L, LoopInfo *LI,
131 AliasAnalysis *AA);
132};
133
134struct LegacyLICMPass : public LoopPass {
135 static char ID; // Pass identification, replacement for typeid
136 LegacyLICMPass() : LoopPass(ID) {
137 initializeLegacyLICMPassPass(*PassRegistry::getPassRegistry());
138 }
139
140 bool runOnLoop(Loop *L, LPPassManager &LPM) override {
141 if (skipLoop(L)) {
142 // If we have run LICM on a previous loop but now we are skipping
143 // (because we've hit the opt-bisect limit), we need to clear the
144 // loop alias information.
145 for (auto &LTAS : LICM.getLoopToAliasSetMap())
146 delete LTAS.second;
147 LICM.getLoopToAliasSetMap().clear();
148 return false;
149 }
150
151 auto *SE = getAnalysisIfAvailable<ScalarEvolutionWrapperPass>();
152 MemorySSA *MSSA = EnableMSSALoopDependency
153 ? (&getAnalysis<MemorySSAWrapperPass>().getMSSA())
154 : nullptr;
155 // For the old PM, we can't use OptimizationRemarkEmitter as an analysis
156 // pass. Function analyses need to be preserved across loop transformations
157 // but ORE cannot be preserved (see comment before the pass definition).
158 OptimizationRemarkEmitter ORE(L->getHeader()->getParent());
159 return LICM.runOnLoop(L,
160 &getAnalysis<AAResultsWrapperPass>().getAAResults(),
161 &getAnalysis<LoopInfoWrapperPass>().getLoopInfo(),
162 &getAnalysis<DominatorTreeWrapperPass>().getDomTree(),
163 &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(),
164 &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(
165 *L->getHeader()->getParent()),
166 SE ? &SE->getSE() : nullptr, MSSA, &ORE, false);
167 }
168
169 /// This transformation requires natural loop information & requires that
170 /// loop preheaders be inserted into the CFG...
171 ///
172 void getAnalysisUsage(AnalysisUsage &AU) const override {
173 AU.addPreserved<DominatorTreeWrapperPass>();
174 AU.addPreserved<LoopInfoWrapperPass>();
175 AU.addRequired<TargetLibraryInfoWrapperPass>();
176 if (EnableMSSALoopDependency)
177 AU.addRequired<MemorySSAWrapperPass>();
178 AU.addRequired<TargetTransformInfoWrapperPass>();
179 getLoopAnalysisUsage(AU);
180 }
181
182 using llvm::Pass::doFinalization;
183
184 bool doFinalization() override {
185 assert(LICM.getLoopToAliasSetMap().empty() &&(static_cast <bool> (LICM.getLoopToAliasSetMap().empty(
) && "Didn't free loop alias sets") ? void (0) : __assert_fail
("LICM.getLoopToAliasSetMap().empty() && \"Didn't free loop alias sets\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 186, __extension__ __PRETTY_FUNCTION__))
186 "Didn't free loop alias sets")(static_cast <bool> (LICM.getLoopToAliasSetMap().empty(
) && "Didn't free loop alias sets") ? void (0) : __assert_fail
("LICM.getLoopToAliasSetMap().empty() && \"Didn't free loop alias sets\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 186, __extension__ __PRETTY_FUNCTION__))
;
187 return false;
188 }
189
190private:
191 LoopInvariantCodeMotion LICM;
192
193 /// cloneBasicBlockAnalysis - Simple Analysis hook. Clone alias set info.
194 void cloneBasicBlockAnalysis(BasicBlock *From, BasicBlock *To,
195 Loop *L) override;
196
197 /// deleteAnalysisValue - Simple Analysis hook. Delete value V from alias
198 /// set.
199 void deleteAnalysisValue(Value *V, Loop *L) override;
200
201 /// Simple Analysis hook. Delete loop L from alias set map.
202 void deleteAnalysisLoop(Loop *L) override;
203};
204} // namespace
205
206PreservedAnalyses LICMPass::run(Loop &L, LoopAnalysisManager &AM,
207 LoopStandardAnalysisResults &AR, LPMUpdater &) {
208 const auto &FAM =
209 AM.getResult<FunctionAnalysisManagerLoopProxy>(L, AR).getManager();
210 Function *F = L.getHeader()->getParent();
211
212 auto *ORE = FAM.getCachedResult<OptimizationRemarkEmitterAnalysis>(*F);
213 // FIXME: This should probably be optional rather than required.
214 if (!ORE)
1
Assuming 'ORE' is non-null
2
Taking false branch
215 report_fatal_error("LICM: OptimizationRemarkEmitterAnalysis not "
216 "cached at a higher level");
217
218 LoopInvariantCodeMotion LICM;
219 if (!LICM.runOnLoop(&L, &AR.AA, &AR.LI, &AR.DT, &AR.TLI, &AR.TTI, &AR.SE,
3
Calling 'LoopInvariantCodeMotion::runOnLoop'
220 AR.MSSA, ORE, true))
221 return PreservedAnalyses::all();
222
223 auto PA = getLoopPassPreservedAnalyses();
224
225 PA.preserve<DominatorTreeAnalysis>();
226 PA.preserve<LoopAnalysis>();
227
228 return PA;
229}
230
231char LegacyLICMPass::ID = 0;
232INITIALIZE_PASS_BEGIN(LegacyLICMPass, "licm", "Loop Invariant Code Motion",static void *initializeLegacyLICMPassPassOnce(PassRegistry &
Registry) {
233 false, false)static void *initializeLegacyLICMPassPassOnce(PassRegistry &
Registry) {
234INITIALIZE_PASS_DEPENDENCY(LoopPass)initializeLoopPassPass(Registry);
235INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)initializeTargetLibraryInfoWrapperPassPass(Registry);
236INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)initializeTargetTransformInfoWrapperPassPass(Registry);
237INITIALIZE_PASS_DEPENDENCY(MemorySSAWrapperPass)initializeMemorySSAWrapperPassPass(Registry);
238INITIALIZE_PASS_END(LegacyLICMPass, "licm", "Loop Invariant Code Motion", false,PassInfo *PI = new PassInfo( "Loop Invariant Code Motion", "licm"
, &LegacyLICMPass::ID, PassInfo::NormalCtor_t(callDefaultCtor
<LegacyLICMPass>), false, false); Registry.registerPass
(*PI, true); return PI; } static llvm::once_flag InitializeLegacyLICMPassPassFlag
; void llvm::initializeLegacyLICMPassPass(PassRegistry &Registry
) { llvm::call_once(InitializeLegacyLICMPassPassFlag, initializeLegacyLICMPassPassOnce
, std::ref(Registry)); }
239 false)PassInfo *PI = new PassInfo( "Loop Invariant Code Motion", "licm"
, &LegacyLICMPass::ID, PassInfo::NormalCtor_t(callDefaultCtor
<LegacyLICMPass>), false, false); Registry.registerPass
(*PI, true); return PI; } static llvm::once_flag InitializeLegacyLICMPassPassFlag
; void llvm::initializeLegacyLICMPassPass(PassRegistry &Registry
) { llvm::call_once(InitializeLegacyLICMPassPassFlag, initializeLegacyLICMPassPassOnce
, std::ref(Registry)); }
240
241Pass *llvm::createLICMPass() { return new LegacyLICMPass(); }
242
243/// Hoist expressions out of the specified loop. Note, alias info for inner
244/// loop is not preserved so it is not a good idea to run LICM multiple
245/// times on one loop.
246/// We should delete AST for inner loops in the new pass manager to avoid
247/// memory leak.
248///
249bool LoopInvariantCodeMotion::runOnLoop(
250 Loop *L, AliasAnalysis *AA, LoopInfo *LI, DominatorTree *DT,
251 TargetLibraryInfo *TLI, TargetTransformInfo *TTI, ScalarEvolution *SE,
252 MemorySSA *MSSA, OptimizationRemarkEmitter *ORE, bool DeleteAST) {
253 bool Changed = false;
254
255 assert(L->isLCSSAForm(*DT) && "Loop is not in LCSSA form.")(static_cast <bool> (L->isLCSSAForm(*DT) && "Loop is not in LCSSA form."
) ? void (0) : __assert_fail ("L->isLCSSAForm(*DT) && \"Loop is not in LCSSA form.\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 255, __extension__ __PRETTY_FUNCTION__))
;
256
257 AliasSetTracker *CurAST = collectAliasInfoForLoop(L, LI, AA);
258
259 // Get the preheader block to move instructions into...
260 BasicBlock *Preheader = L->getLoopPreheader();
261
262 // Compute loop safety information.
263 LoopSafetyInfo SafetyInfo;
264 computeLoopSafetyInfo(&SafetyInfo, L);
265
266 // We want to visit all of the instructions in this loop... that are not parts
267 // of our subloops (they have already had their invariants hoisted out of
268 // their loop, into this loop, so there is no need to process the BODIES of
269 // the subloops).
270 //
271 // Traverse the body of the loop in depth first order on the dominator tree so
272 // that we are guaranteed to see definitions before we see uses. This allows
273 // us to sink instructions in one pass, without iteration. After sinking
274 // instructions, we perform another pass to hoist them out of the loop.
275 //
276 if (L->hasDedicatedExits())
4
Assuming the condition is false
5
Taking false branch
277 Changed |= sinkRegion(DT->getNode(L->getHeader()), AA, LI, DT, TLI, TTI, L,
278 CurAST, &SafetyInfo, ORE);
279 if (Preheader)
6
Assuming 'Preheader' is non-null
7
Taking true branch
280 Changed |= hoistRegion(DT->getNode(L->getHeader()), AA, LI, DT, TLI, L,
8
Calling 'hoistRegion'
281 CurAST, &SafetyInfo, ORE);
282
283 // Now that all loop invariants have been removed from the loop, promote any
284 // memory references to scalars that we can.
285 // Don't sink stores from loops without dedicated block exits. Exits
286 // containing indirect branches are not transformed by loop simplify,
287 // make sure we catch that. An additional load may be generated in the
288 // preheader for SSA updater, so also avoid sinking when no preheader
289 // is available.
290 if (!DisablePromotion && Preheader && L->hasDedicatedExits()) {
291 // Figure out the loop exits and their insertion points
292 SmallVector<BasicBlock *, 8> ExitBlocks;
293 L->getUniqueExitBlocks(ExitBlocks);
294
295 // We can't insert into a catchswitch.
296 bool HasCatchSwitch = llvm::any_of(ExitBlocks, [](BasicBlock *Exit) {
297 return isa<CatchSwitchInst>(Exit->getTerminator());
298 });
299
300 if (!HasCatchSwitch) {
301 SmallVector<Instruction *, 8> InsertPts;
302 InsertPts.reserve(ExitBlocks.size());
303 for (BasicBlock *ExitBlock : ExitBlocks)
304 InsertPts.push_back(&*ExitBlock->getFirstInsertionPt());
305
306 PredIteratorCache PIC;
307
308 bool Promoted = false;
309
310 // Loop over all of the alias sets in the tracker object.
311 for (AliasSet &AS : *CurAST) {
312 // We can promote this alias set if it has a store, if it is a "Must"
313 // alias set, if the pointer is loop invariant, and if we are not
314 // eliminating any volatile loads or stores.
315 if (AS.isForwardingAliasSet() || !AS.isMod() || !AS.isMustAlias() ||
316 AS.isVolatile() || !L->isLoopInvariant(AS.begin()->getValue()))
317 continue;
318
319 assert((static_cast <bool> (!AS.empty() && "Must alias set should have at least one pointer element in it!"
) ? void (0) : __assert_fail ("!AS.empty() && \"Must alias set should have at least one pointer element in it!\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 321, __extension__ __PRETTY_FUNCTION__))
320 !AS.empty() &&(static_cast <bool> (!AS.empty() && "Must alias set should have at least one pointer element in it!"
) ? void (0) : __assert_fail ("!AS.empty() && \"Must alias set should have at least one pointer element in it!\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 321, __extension__ __PRETTY_FUNCTION__))
321 "Must alias set should have at least one pointer element in it!")(static_cast <bool> (!AS.empty() && "Must alias set should have at least one pointer element in it!"
) ? void (0) : __assert_fail ("!AS.empty() && \"Must alias set should have at least one pointer element in it!\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 321, __extension__ __PRETTY_FUNCTION__))
;
322
323 SmallSetVector<Value *, 8> PointerMustAliases;
324 for (const auto &ASI : AS)
325 PointerMustAliases.insert(ASI.getValue());
326
327 Promoted |= promoteLoopAccessesToScalars(PointerMustAliases, ExitBlocks,
328 InsertPts, PIC, LI, DT, TLI, L,
329 CurAST, &SafetyInfo, ORE);
330 }
331
332 // Once we have promoted values across the loop body we have to
333 // recursively reform LCSSA as any nested loop may now have values defined
334 // within the loop used in the outer loop.
335 // FIXME: This is really heavy handed. It would be a bit better to use an
336 // SSAUpdater strategy during promotion that was LCSSA aware and reformed
337 // it as it went.
338 if (Promoted)
339 formLCSSARecursively(*L, *DT, LI, SE);
340
341 Changed |= Promoted;
342 }
343 }
344
345 // Check that neither this loop nor its parent have had LCSSA broken. LICM is
346 // specifically moving instructions across the loop boundary and so it is
347 // especially in need of sanity checking here.
348 assert(L->isLCSSAForm(*DT) && "Loop not left in LCSSA form after LICM!")(static_cast <bool> (L->isLCSSAForm(*DT) && "Loop not left in LCSSA form after LICM!"
) ? void (0) : __assert_fail ("L->isLCSSAForm(*DT) && \"Loop not left in LCSSA form after LICM!\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 348, __extension__ __PRETTY_FUNCTION__))
;
349 assert((!L->getParentLoop() || L->getParentLoop()->isLCSSAForm(*DT)) &&(static_cast <bool> ((!L->getParentLoop() || L->getParentLoop
()->isLCSSAForm(*DT)) && "Parent loop not left in LCSSA form after LICM!"
) ? void (0) : __assert_fail ("(!L->getParentLoop() || L->getParentLoop()->isLCSSAForm(*DT)) && \"Parent loop not left in LCSSA form after LICM!\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 350, __extension__ __PRETTY_FUNCTION__))
350 "Parent loop not left in LCSSA form after LICM!")(static_cast <bool> ((!L->getParentLoop() || L->getParentLoop
()->isLCSSAForm(*DT)) && "Parent loop not left in LCSSA form after LICM!"
) ? void (0) : __assert_fail ("(!L->getParentLoop() || L->getParentLoop()->isLCSSAForm(*DT)) && \"Parent loop not left in LCSSA form after LICM!\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 350, __extension__ __PRETTY_FUNCTION__))
;
351
352 // If this loop is nested inside of another one, save the alias information
353 // for when we process the outer loop.
354 if (L->getParentLoop() && !DeleteAST)
355 LoopToAliasSetMap[L] = CurAST;
356 else
357 delete CurAST;
358
359 if (Changed && SE)
360 SE->forgetLoopDispositions(L);
361 return Changed;
362}
363
364/// Walk the specified region of the CFG (defined by all blocks dominated by
365/// the specified block, and that are in the current loop) in reverse depth
366/// first order w.r.t the DominatorTree. This allows us to visit uses before
367/// definitions, allowing us to sink a loop body in one pass without iteration.
368///
369bool llvm::sinkRegion(DomTreeNode *N, AliasAnalysis *AA, LoopInfo *LI,
370 DominatorTree *DT, TargetLibraryInfo *TLI,
371 TargetTransformInfo *TTI, Loop *CurLoop,
372 AliasSetTracker *CurAST, LoopSafetyInfo *SafetyInfo,
373 OptimizationRemarkEmitter *ORE) {
374
375 // Verify inputs.
376 assert(N != nullptr && AA != nullptr && LI != nullptr && DT != nullptr &&(static_cast <bool> (N != nullptr && AA != nullptr
&& LI != nullptr && DT != nullptr &&
CurLoop != nullptr && CurAST != nullptr && SafetyInfo
!= nullptr && "Unexpected input to sinkRegion") ? void
(0) : __assert_fail ("N != nullptr && AA != nullptr && LI != nullptr && DT != nullptr && CurLoop != nullptr && CurAST != nullptr && SafetyInfo != nullptr && \"Unexpected input to sinkRegion\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 378, __extension__ __PRETTY_FUNCTION__))
377 CurLoop != nullptr && CurAST != nullptr && SafetyInfo != nullptr &&(static_cast <bool> (N != nullptr && AA != nullptr
&& LI != nullptr && DT != nullptr &&
CurLoop != nullptr && CurAST != nullptr && SafetyInfo
!= nullptr && "Unexpected input to sinkRegion") ? void
(0) : __assert_fail ("N != nullptr && AA != nullptr && LI != nullptr && DT != nullptr && CurLoop != nullptr && CurAST != nullptr && SafetyInfo != nullptr && \"Unexpected input to sinkRegion\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 378, __extension__ __PRETTY_FUNCTION__))
378 "Unexpected input to sinkRegion")(static_cast <bool> (N != nullptr && AA != nullptr
&& LI != nullptr && DT != nullptr &&
CurLoop != nullptr && CurAST != nullptr && SafetyInfo
!= nullptr && "Unexpected input to sinkRegion") ? void
(0) : __assert_fail ("N != nullptr && AA != nullptr && LI != nullptr && DT != nullptr && CurLoop != nullptr && CurAST != nullptr && SafetyInfo != nullptr && \"Unexpected input to sinkRegion\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 378, __extension__ __PRETTY_FUNCTION__))
;
379
380 // We want to visit children before parents. We will enque all the parents
381 // before their children in the worklist and process the worklist in reverse
382 // order.
383 SmallVector<DomTreeNode *, 16> Worklist = collectChildrenInLoop(N, CurLoop);
384
385 bool Changed = false;
386 for (DomTreeNode *DTN : reverse(Worklist)) {
387 BasicBlock *BB = DTN->getBlock();
388 // Only need to process the contents of this block if it is not part of a
389 // subloop (which would already have been processed).
390 if (inSubLoop(BB, CurLoop, LI))
391 continue;
392
393 for (BasicBlock::iterator II = BB->end(); II != BB->begin();) {
394 Instruction &I = *--II;
395
396 // If the instruction is dead, we would try to sink it because it isn't
397 // used in the loop, instead, just delete it.
398 if (isInstructionTriviallyDead(&I, TLI)) {
399 LLVM_DEBUG(dbgs() << "LICM deleting dead inst: " << I << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("licm")) { dbgs() << "LICM deleting dead inst: " <<
I << '\n'; } } while (false)
;
400 salvageDebugInfo(I);
401 ++II;
402 CurAST->deleteValue(&I);
403 I.eraseFromParent();
404 Changed = true;
405 continue;
406 }
407
408 // Check to see if we can sink this instruction to the exit blocks
409 // of the loop. We can do this if the all users of the instruction are
410 // outside of the loop. In this case, it doesn't even matter if the
411 // operands of the instruction are loop invariant.
412 //
413 bool FreeInLoop = false;
414 if (isNotUsedOrFreeInLoop(I, CurLoop, SafetyInfo, TTI, FreeInLoop) &&
415 canSinkOrHoistInst(I, AA, DT, CurLoop, CurAST, SafetyInfo, ORE)) {
416 if (sink(I, LI, DT, CurLoop, SafetyInfo, ORE, FreeInLoop)) {
417 if (!FreeInLoop) {
418 ++II;
419 CurAST->deleteValue(&I);
420 I.eraseFromParent();
421 }
422 Changed = true;
423 }
424 }
425 }
426 }
427 return Changed;
428}
429
430/// Walk the specified region of the CFG (defined by all blocks dominated by
431/// the specified block, and that are in the current loop) in depth first
432/// order w.r.t the DominatorTree. This allows us to visit definitions before
433/// uses, allowing us to hoist a loop body in one pass without iteration.
434///
435bool llvm::hoistRegion(DomTreeNode *N, AliasAnalysis *AA, LoopInfo *LI,
436 DominatorTree *DT, TargetLibraryInfo *TLI, Loop *CurLoop,
437 AliasSetTracker *CurAST, LoopSafetyInfo *SafetyInfo,
438 OptimizationRemarkEmitter *ORE) {
439 // Verify inputs.
440 assert(N != nullptr && AA != nullptr && LI != nullptr && DT != nullptr &&(static_cast <bool> (N != nullptr && AA != nullptr
&& LI != nullptr && DT != nullptr &&
CurLoop != nullptr && CurAST != nullptr && SafetyInfo
!= nullptr && "Unexpected input to hoistRegion") ? void
(0) : __assert_fail ("N != nullptr && AA != nullptr && LI != nullptr && DT != nullptr && CurLoop != nullptr && CurAST != nullptr && SafetyInfo != nullptr && \"Unexpected input to hoistRegion\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 442, __extension__ __PRETTY_FUNCTION__))
441 CurLoop != nullptr && CurAST != nullptr && SafetyInfo != nullptr &&(static_cast <bool> (N != nullptr && AA != nullptr
&& LI != nullptr && DT != nullptr &&
CurLoop != nullptr && CurAST != nullptr && SafetyInfo
!= nullptr && "Unexpected input to hoistRegion") ? void
(0) : __assert_fail ("N != nullptr && AA != nullptr && LI != nullptr && DT != nullptr && CurLoop != nullptr && CurAST != nullptr && SafetyInfo != nullptr && \"Unexpected input to hoistRegion\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 442, __extension__ __PRETTY_FUNCTION__))
442 "Unexpected input to hoistRegion")(static_cast <bool> (N != nullptr && AA != nullptr
&& LI != nullptr && DT != nullptr &&
CurLoop != nullptr && CurAST != nullptr && SafetyInfo
!= nullptr && "Unexpected input to hoistRegion") ? void
(0) : __assert_fail ("N != nullptr && AA != nullptr && LI != nullptr && DT != nullptr && CurLoop != nullptr && CurAST != nullptr && SafetyInfo != nullptr && \"Unexpected input to hoistRegion\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 442, __extension__ __PRETTY_FUNCTION__))
;
443
444 // We want to visit parents before children. We will enque all the parents
445 // before their children in the worklist and process the worklist in order.
446 SmallVector<DomTreeNode *, 16> Worklist = collectChildrenInLoop(N, CurLoop);
447
448 bool Changed = false;
449 for (DomTreeNode *DTN : Worklist) {
9
Assuming '__begin1' is not equal to '__end1'
450 BasicBlock *BB = DTN->getBlock();
451 // Only need to process the contents of this block if it is not part of a
452 // subloop (which would already have been processed).
453 if (inSubLoop(BB, CurLoop, LI))
10
Taking false branch
454 continue;
455
456 // Keep track of whether the prefix of instructions visited so far are such
457 // that the next instruction visited is guaranteed to execute if the loop
458 // is entered.
459 bool IsMustExecute = CurLoop->getHeader() == BB;
11
Assuming the condition is false
460
461 for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E;) {
12
Loop condition is true. Entering loop body
462 Instruction &I = *II++;
463 // Try constant folding this instruction. If all the operands are
464 // constants, it is technically hoistable, but it would be better to
465 // just fold it.
466 if (Constant *C = ConstantFoldInstruction(
13
Assuming 'C' is null
14
Taking false branch
467 &I, I.getModule()->getDataLayout(), TLI)) {
468 LLVM_DEBUG(dbgs() << "LICM folding inst: " << I << " --> " << *Cdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("licm")) { dbgs() << "LICM folding inst: " << I <<
" --> " << *C << '\n'; } } while (false)
469 << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("licm")) { dbgs() << "LICM folding inst: " << I <<
" --> " << *C << '\n'; } } while (false)
;
470 CurAST->copyValue(&I, C);
471 I.replaceAllUsesWith(C);
472 if (isInstructionTriviallyDead(&I, TLI)) {
473 CurAST->deleteValue(&I);
474 I.eraseFromParent();
475 }
476 Changed = true;
477 continue;
478 }
479
480 // Try hoisting the instruction out to the preheader. We can only do
481 // this if all of the operands of the instruction are loop invariant and
482 // if it is safe to hoist the instruction.
483 //
484 if (CurLoop->hasLoopInvariantOperands(&I) &&
15
Assuming the condition is true
485 canSinkOrHoistInst(I, AA, DT, CurLoop, CurAST, SafetyInfo, ORE) &&
16
Calling 'canSinkOrHoistInst'
486 (IsMustExecute ||
487 isSafeToExecuteUnconditionally(
488 I, DT, CurLoop, SafetyInfo, ORE,
489 CurLoop->getLoopPreheader()->getTerminator()))) {
490 Changed |= hoist(I, DT, CurLoop, SafetyInfo, ORE);
491 continue;
492 }
493
494 // Attempt to remove floating point division out of the loop by
495 // converting it to a reciprocal multiplication.
496 if (I.getOpcode() == Instruction::FDiv &&
497 CurLoop->isLoopInvariant(I.getOperand(1)) &&
498 I.hasAllowReciprocal()) {
499 auto Divisor = I.getOperand(1);
500 auto One = llvm::ConstantFP::get(Divisor->getType(), 1.0);
501 auto ReciprocalDivisor = BinaryOperator::CreateFDiv(One, Divisor);
502 ReciprocalDivisor->setFastMathFlags(I.getFastMathFlags());
503 ReciprocalDivisor->insertBefore(&I);
504
505 auto Product =
506 BinaryOperator::CreateFMul(I.getOperand(0), ReciprocalDivisor);
507 Product->setFastMathFlags(I.getFastMathFlags());
508 Product->insertAfter(&I);
509 I.replaceAllUsesWith(Product);
510 I.eraseFromParent();
511
512 hoist(*ReciprocalDivisor, DT, CurLoop, SafetyInfo, ORE);
513 Changed = true;
514 continue;
515 }
516
517 if (IsMustExecute)
518 IsMustExecute = isGuaranteedToTransferExecutionToSuccessor(&I);
519 }
520 }
521
522 return Changed;
523}
524
525// Return true if LI is invariant within scope of the loop. LI is invariant if
526// CurLoop is dominated by an invariant.start representing the same memory
527// location and size as the memory location LI loads from, and also the
528// invariant.start has no uses.
529static bool isLoadInvariantInLoop(LoadInst *LI, DominatorTree *DT,
530 Loop *CurLoop) {
531 Value *Addr = LI->getOperand(0);
532 const DataLayout &DL = LI->getModule()->getDataLayout();
533 const uint32_t LocSizeInBits = DL.getTypeSizeInBits(
534 cast<PointerType>(Addr->getType())->getElementType());
535
536 // if the type is i8 addrspace(x)*, we know this is the type of
537 // llvm.invariant.start operand
538 auto *PtrInt8Ty = PointerType::get(Type::getInt8Ty(LI->getContext()),
539 LI->getPointerAddressSpace());
540 unsigned BitcastsVisited = 0;
541 // Look through bitcasts until we reach the i8* type (this is invariant.start
542 // operand type).
543 while (Addr->getType() != PtrInt8Ty) {
544 auto *BC = dyn_cast<BitCastInst>(Addr);
545 // Avoid traversing high number of bitcast uses.
546 if (++BitcastsVisited > MaxNumUsesTraversed || !BC)
547 return false;
548 Addr = BC->getOperand(0);
549 }
550
551 unsigned UsesVisited = 0;
552 // Traverse all uses of the load operand value, to see if invariant.start is
553 // one of the uses, and whether it dominates the load instruction.
554 for (auto *U : Addr->users()) {
555 // Avoid traversing for Load operand with high number of users.
556 if (++UsesVisited > MaxNumUsesTraversed)
557 return false;
558 IntrinsicInst *II = dyn_cast<IntrinsicInst>(U);
559 // If there are escaping uses of invariant.start instruction, the load maybe
560 // non-invariant.
561 if (!II || II->getIntrinsicID() != Intrinsic::invariant_start ||
562 !II->use_empty())
563 continue;
564 unsigned InvariantSizeInBits =
565 cast<ConstantInt>(II->getArgOperand(0))->getSExtValue() * 8;
566 // Confirm the invariant.start location size contains the load operand size
567 // in bits. Also, the invariant.start should dominate the load, and we
568 // should not hoist the load out of a loop that contains this dominating
569 // invariant.start.
570 if (LocSizeInBits <= InvariantSizeInBits &&
571 DT->properlyDominates(II->getParent(), CurLoop->getHeader()))
572 return true;
573 }
574
575 return false;
576}
577
578bool llvm::canSinkOrHoistInst(Instruction &I, AAResults *AA, DominatorTree *DT,
579 Loop *CurLoop, AliasSetTracker *CurAST,
580 LoopSafetyInfo *SafetyInfo,
581 OptimizationRemarkEmitter *ORE) {
582 // SafetyInfo is nullptr if we are checking for sinking from preheader to
583 // loop body.
584 const bool SinkingToLoopBody = !SafetyInfo;
585 // Loads have extra constraints we have to verify before we can hoist them.
586 if (LoadInst *LI = dyn_cast<LoadInst>(&I)) {
17
Taking false branch
587 if (!LI->isUnordered())
588 return false; // Don't sink/hoist volatile or ordered atomic loads!
589
590 // Loads from constant memory are always safe to move, even if they end up
591 // in the same alias set as something that ends up being modified.
592 if (AA->pointsToConstantMemory(LI->getOperand(0)))
593 return true;
594 if (LI->getMetadata(LLVMContext::MD_invariant_load))
595 return true;
596
597 if (LI->isAtomic() && SinkingToLoopBody)
598 return false; // Don't sink unordered atomic loads to loop body.
599
600 // This checks for an invariant.start dominating the load.
601 if (isLoadInvariantInLoop(LI, DT, CurLoop))
602 return true;
603
604 // Don't hoist loads which have may-aliased stores in loop.
605 uint64_t Size = 0;
606 if (LI->getType()->isSized())
607 Size = I.getModule()->getDataLayout().getTypeStoreSize(LI->getType());
608
609 AAMDNodes AAInfo;
610 LI->getAAMetadata(AAInfo);
611
612 bool Invalidated =
613 pointerInvalidatedByLoop(LI->getOperand(0), Size, AAInfo, CurAST);
614 // Check loop-invariant address because this may also be a sinkable load
615 // whose address is not necessarily loop-invariant.
616 if (ORE && Invalidated && CurLoop->isLoopInvariant(LI->getPointerOperand()))
617 ORE->emit([&]() {
618 return OptimizationRemarkMissed(
619 DEBUG_TYPE"licm", "LoadWithLoopInvariantAddressInvalidated", LI)
620 << "failed to move load with loop-invariant address "
621 "because the loop may invalidate its value";
622 });
623
624 return !Invalidated;
625 } else if (CallInst *CI = dyn_cast<CallInst>(&I)) {
18
Taking false branch
626 // Don't sink or hoist dbg info; it's legal, but not useful.
627 if (isa<DbgInfoIntrinsic>(I))
628 return false;
629
630 // Don't sink calls which can throw.
631 if (CI->mayThrow())
632 return false;
633
634 // Handle simple cases by querying alias analysis.
635 FunctionModRefBehavior Behavior = AA->getModRefBehavior(CI);
636 if (Behavior == FMRB_DoesNotAccessMemory)
637 return true;
638 if (AliasAnalysis::onlyReadsMemory(Behavior)) {
639 // A readonly argmemonly function only reads from memory pointed to by
640 // it's arguments with arbitrary offsets. If we can prove there are no
641 // writes to this memory in the loop, we can hoist or sink.
642 if (AliasAnalysis::onlyAccessesArgPointees(Behavior)) {
643 for (Value *Op : CI->arg_operands())
644 if (Op->getType()->isPointerTy() &&
645 pointerInvalidatedByLoop(Op, MemoryLocation::UnknownSize,
646 AAMDNodes(), CurAST))
647 return false;
648 return true;
649 }
650 // If this call only reads from memory and there are no writes to memory
651 // in the loop, we can hoist or sink the call as appropriate.
652 bool FoundMod = false;
653 for (AliasSet &AS : *CurAST) {
654 if (!AS.isForwardingAliasSet() && AS.isMod()) {
655 FoundMod = true;
656 break;
657 }
658 }
659 if (!FoundMod)
660 return true;
661 }
662
663 // FIXME: This should use mod/ref information to see if we can hoist or
664 // sink the call.
665
666 return false;
667 }
668
669 // Only these instructions are hoistable/sinkable.
670 if (!isa<BinaryOperator>(I) && !isa<CastInst>(I) && !isa<SelectInst>(I) &&
671 !isa<GetElementPtrInst>(I) && !isa<CmpInst>(I) &&
672 !isa<InsertElementInst>(I) && !isa<ExtractElementInst>(I) &&
673 !isa<ShuffleVectorInst>(I) && !isa<ExtractValueInst>(I) &&
674 !isa<InsertValueInst>(I))
675 return false;
676
677 // If we are checking for sinking from preheader to loop body it will be
678 // always safe as there is no speculative execution.
679 if (SinkingToLoopBody)
19
Taking false branch
680 return true;
681
682 // TODO: Plumb the context instruction through to make hoisting and sinking
683 // more powerful. Hoisting of loads already works due to the special casing
684 // above.
685 return isSafeToExecuteUnconditionally(I, DT, CurLoop, SafetyInfo, nullptr);
20
Passing null pointer value via 5th parameter 'ORE'
21
Calling 'isSafeToExecuteUnconditionally'
686}
687
688/// Returns true if a PHINode is a trivially replaceable with an
689/// Instruction.
690/// This is true when all incoming values are that instruction.
691/// This pattern occurs most often with LCSSA PHI nodes.
692///
693static bool isTriviallyReplaceablePHI(const PHINode &PN, const Instruction &I) {
694 for (const Value *IncValue : PN.incoming_values())
695 if (IncValue != &I)
696 return false;
697
698 return true;
699}
700
701/// Return true if the instruction is free in the loop.
702static bool isFreeInLoop(const Instruction &I, const Loop *CurLoop,
703 const TargetTransformInfo *TTI) {
704
705 if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(&I)) {
706 if (TTI->getUserCost(GEP) != TargetTransformInfo::TCC_Free)
707 return false;
708 // For a GEP, we cannot simply use getUserCost because currently it
709 // optimistically assume that a GEP will fold into addressing mode
710 // regardless of its users.
711 const BasicBlock *BB = GEP->getParent();
712 for (const User *U : GEP->users()) {
713 const Instruction *UI = cast<Instruction>(U);
714 if (CurLoop->contains(UI) &&
715 (BB != UI->getParent() ||
716 (!isa<StoreInst>(UI) && !isa<LoadInst>(UI))))
717 return false;
718 }
719 return true;
720 } else
721 return TTI->getUserCost(&I) == TargetTransformInfo::TCC_Free;
722}
723
724/// Return true if the only users of this instruction are outside of
725/// the loop. If this is true, we can sink the instruction to the exit
726/// blocks of the loop.
727///
728/// We also return true if the instruction could be folded away in lowering.
729/// (e.g., a GEP can be folded into a load as an addressing mode in the loop).
730static bool isNotUsedOrFreeInLoop(const Instruction &I, const Loop *CurLoop,
731 const LoopSafetyInfo *SafetyInfo,
732 TargetTransformInfo *TTI, bool &FreeInLoop) {
733 const auto &BlockColors = SafetyInfo->BlockColors;
734 bool IsFree = isFreeInLoop(I, CurLoop, TTI);
735 for (const User *U : I.users()) {
736 const Instruction *UI = cast<Instruction>(U);
737 if (const PHINode *PN = dyn_cast<PHINode>(UI)) {
738 const BasicBlock *BB = PN->getParent();
739 // We cannot sink uses in catchswitches.
740 if (isa<CatchSwitchInst>(BB->getTerminator()))
741 return false;
742
743 // We need to sink a callsite to a unique funclet. Avoid sinking if the
744 // phi use is too muddled.
745 if (isa<CallInst>(I))
746 if (!BlockColors.empty() &&
747 BlockColors.find(const_cast<BasicBlock *>(BB))->second.size() != 1)
748 return false;
749 }
750
751 if (CurLoop->contains(UI)) {
752 if (IsFree) {
753 FreeInLoop = true;
754 continue;
755 }
756 return false;
757 }
758 }
759 return true;
760}
761
762static Instruction *
763CloneInstructionInExitBlock(Instruction &I, BasicBlock &ExitBlock, PHINode &PN,
764 const LoopInfo *LI,
765 const LoopSafetyInfo *SafetyInfo) {
766 Instruction *New;
767 if (auto *CI = dyn_cast<CallInst>(&I)) {
768 const auto &BlockColors = SafetyInfo->BlockColors;
769
770 // Sinking call-sites need to be handled differently from other
771 // instructions. The cloned call-site needs a funclet bundle operand
772 // appropriate for it's location in the CFG.
773 SmallVector<OperandBundleDef, 1> OpBundles;
774 for (unsigned BundleIdx = 0, BundleEnd = CI->getNumOperandBundles();
775 BundleIdx != BundleEnd; ++BundleIdx) {
776 OperandBundleUse Bundle = CI->getOperandBundleAt(BundleIdx);
777 if (Bundle.getTagID() == LLVMContext::OB_funclet)
778 continue;
779
780 OpBundles.emplace_back(Bundle);
781 }
782
783 if (!BlockColors.empty()) {
784 const ColorVector &CV = BlockColors.find(&ExitBlock)->second;
785 assert(CV.size() == 1 && "non-unique color for exit block!")(static_cast <bool> (CV.size() == 1 && "non-unique color for exit block!"
) ? void (0) : __assert_fail ("CV.size() == 1 && \"non-unique color for exit block!\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 785, __extension__ __PRETTY_FUNCTION__))
;
786 BasicBlock *BBColor = CV.front();
787 Instruction *EHPad = BBColor->getFirstNonPHI();
788 if (EHPad->isEHPad())
789 OpBundles.emplace_back("funclet", EHPad);
790 }
791
792 New = CallInst::Create(CI, OpBundles);
793 } else {
794 New = I.clone();
795 }
796
797 ExitBlock.getInstList().insert(ExitBlock.getFirstInsertionPt(), New);
798 if (!I.getName().empty())
799 New->setName(I.getName() + ".le");
800
801 // Build LCSSA PHI nodes for any in-loop operands. Note that this is
802 // particularly cheap because we can rip off the PHI node that we're
803 // replacing for the number and blocks of the predecessors.
804 // OPT: If this shows up in a profile, we can instead finish sinking all
805 // invariant instructions, and then walk their operands to re-establish
806 // LCSSA. That will eliminate creating PHI nodes just to nuke them when
807 // sinking bottom-up.
808 for (User::op_iterator OI = New->op_begin(), OE = New->op_end(); OI != OE;
809 ++OI)
810 if (Instruction *OInst = dyn_cast<Instruction>(*OI))
811 if (Loop *OLoop = LI->getLoopFor(OInst->getParent()))
812 if (!OLoop->contains(&PN)) {
813 PHINode *OpPN =
814 PHINode::Create(OInst->getType(), PN.getNumIncomingValues(),
815 OInst->getName() + ".lcssa", &ExitBlock.front());
816 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i)
817 OpPN->addIncoming(OInst, PN.getIncomingBlock(i));
818 *OI = OpPN;
819 }
820 return New;
821}
822
823static Instruction *sinkThroughTriviallyReplaceablePHI(
824 PHINode *TPN, Instruction *I, LoopInfo *LI,
825 SmallDenseMap<BasicBlock *, Instruction *, 32> &SunkCopies,
826 const LoopSafetyInfo *SafetyInfo, const Loop *CurLoop) {
827 assert(isTriviallyReplaceablePHI(*TPN, *I) &&(static_cast <bool> (isTriviallyReplaceablePHI(*TPN, *I
) && "Expect only trivially replaceable PHI") ? void (
0) : __assert_fail ("isTriviallyReplaceablePHI(*TPN, *I) && \"Expect only trivially replaceable PHI\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 828, __extension__ __PRETTY_FUNCTION__))
828 "Expect only trivially replaceable PHI")(static_cast <bool> (isTriviallyReplaceablePHI(*TPN, *I
) && "Expect only trivially replaceable PHI") ? void (
0) : __assert_fail ("isTriviallyReplaceablePHI(*TPN, *I) && \"Expect only trivially replaceable PHI\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 828, __extension__ __PRETTY_FUNCTION__))
;
829 BasicBlock *ExitBlock = TPN->getParent();
830 Instruction *New;
831 auto It = SunkCopies.find(ExitBlock);
832 if (It != SunkCopies.end())
833 New = It->second;
834 else
835 New = SunkCopies[ExitBlock] =
836 CloneInstructionInExitBlock(*I, *ExitBlock, *TPN, LI, SafetyInfo);
837 return New;
838}
839
840static bool canSplitPredecessors(PHINode *PN, LoopSafetyInfo *SafetyInfo) {
841 BasicBlock *BB = PN->getParent();
842 if (!BB->canSplitPredecessors())
843 return false;
844 // It's not impossible to split EHPad blocks, but if BlockColors already exist
845 // it require updating BlockColors for all offspring blocks accordingly. By
846 // skipping such corner case, we can make updating BlockColors after splitting
847 // predecessor fairly simple.
848 if (!SafetyInfo->BlockColors.empty() && BB->getFirstNonPHI()->isEHPad())
849 return false;
850 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
851 BasicBlock *BBPred = *PI;
852 if (isa<IndirectBrInst>(BBPred->getTerminator()))
853 return false;
854 }
855 return true;
856}
857
858static void splitPredecessorsOfLoopExit(PHINode *PN, DominatorTree *DT,
859 LoopInfo *LI, const Loop *CurLoop,
860 LoopSafetyInfo *SafetyInfo) {
861#ifndef NDEBUG
862 SmallVector<BasicBlock *, 32> ExitBlocks;
863 CurLoop->getUniqueExitBlocks(ExitBlocks);
864 SmallPtrSet<BasicBlock *, 32> ExitBlockSet(ExitBlocks.begin(),
865 ExitBlocks.end());
866#endif
867 BasicBlock *ExitBB = PN->getParent();
868 assert(ExitBlockSet.count(ExitBB) && "Expect the PHI is in an exit block.")(static_cast <bool> (ExitBlockSet.count(ExitBB) &&
"Expect the PHI is in an exit block.") ? void (0) : __assert_fail
("ExitBlockSet.count(ExitBB) && \"Expect the PHI is in an exit block.\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 868, __extension__ __PRETTY_FUNCTION__))
;
869
870 // Split predecessors of the loop exit to make instructions in the loop are
871 // exposed to exit blocks through trivially replaceable PHIs while keeping the
872 // loop in the canonical form where each predecessor of each exit block should
873 // be contained within the loop. For example, this will convert the loop below
874 // from
875 //
876 // LB1:
877 // %v1 =
878 // br %LE, %LB2
879 // LB2:
880 // %v2 =
881 // br %LE, %LB1
882 // LE:
883 // %p = phi [%v1, %LB1], [%v2, %LB2] <-- non-trivially replaceable
884 //
885 // to
886 //
887 // LB1:
888 // %v1 =
889 // br %LE.split, %LB2
890 // LB2:
891 // %v2 =
892 // br %LE.split2, %LB1
893 // LE.split:
894 // %p1 = phi [%v1, %LB1] <-- trivially replaceable
895 // br %LE
896 // LE.split2:
897 // %p2 = phi [%v2, %LB2] <-- trivially replaceable
898 // br %LE
899 // LE:
900 // %p = phi [%p1, %LE.split], [%p2, %LE.split2]
901 //
902 auto &BlockColors = SafetyInfo->BlockColors;
903 SmallSetVector<BasicBlock *, 8> PredBBs(pred_begin(ExitBB), pred_end(ExitBB));
904 while (!PredBBs.empty()) {
905 BasicBlock *PredBB = *PredBBs.begin();
906 assert(CurLoop->contains(PredBB) &&(static_cast <bool> (CurLoop->contains(PredBB) &&
"Expect all predecessors are in the loop") ? void (0) : __assert_fail
("CurLoop->contains(PredBB) && \"Expect all predecessors are in the loop\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 907, __extension__ __PRETTY_FUNCTION__))
907 "Expect all predecessors are in the loop")(static_cast <bool> (CurLoop->contains(PredBB) &&
"Expect all predecessors are in the loop") ? void (0) : __assert_fail
("CurLoop->contains(PredBB) && \"Expect all predecessors are in the loop\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 907, __extension__ __PRETTY_FUNCTION__))
;
908 if (PN->getBasicBlockIndex(PredBB) >= 0) {
909 BasicBlock *NewPred = SplitBlockPredecessors(
910 ExitBB, PredBB, ".split.loop.exit", DT, LI, true);
911 // Since we do not allow splitting EH-block with BlockColors in
912 // canSplitPredecessors(), we can simply assign predecessor's color to
913 // the new block.
914 if (!BlockColors.empty()) {
915 // Grab a reference to the ColorVector to be inserted before getting the
916 // reference to the vector we are copying because inserting the new
917 // element in BlockColors might cause the map to be reallocated.
918 ColorVector &ColorsForNewBlock = BlockColors[NewPred];
919 ColorVector &ColorsForOldBlock = BlockColors[PredBB];
920 ColorsForNewBlock = ColorsForOldBlock;
921 }
922 }
923 PredBBs.remove(PredBB);
924 }
925}
926
927/// When an instruction is found to only be used outside of the loop, this
928/// function moves it to the exit blocks and patches up SSA form as needed.
929/// This method is guaranteed to remove the original instruction from its
930/// position, and may either delete it or move it to outside of the loop.
931///
932static bool sink(Instruction &I, LoopInfo *LI, DominatorTree *DT,
933 const Loop *CurLoop, LoopSafetyInfo *SafetyInfo,
934 OptimizationRemarkEmitter *ORE, bool FreeInLoop) {
935 LLVM_DEBUG(dbgs() << "LICM sinking instruction: " << I << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("licm")) { dbgs() << "LICM sinking instruction: " <<
I << "\n"; } } while (false)
;
936 ORE->emit([&]() {
937 return OptimizationRemark(DEBUG_TYPE"licm", "InstSunk", &I)
938 << "sinking " << ore::NV("Inst", &I);
939 });
940 bool Changed = false;
941 if (isa<LoadInst>(I))
942 ++NumMovedLoads;
943 else if (isa<CallInst>(I))
944 ++NumMovedCalls;
945 ++NumSunk;
946
947 // Iterate over users to be ready for actual sinking. Replace users via
948 // unrechable blocks with undef and make all user PHIs trivially replcable.
949 SmallPtrSet<Instruction *, 8> VisitedUsers;
950 for (Value::user_iterator UI = I.user_begin(), UE = I.user_end(); UI != UE;) {
951 auto *User = cast<Instruction>(*UI);
952 Use &U = UI.getUse();
953 ++UI;
954
955 if (VisitedUsers.count(User) || CurLoop->contains(User))
956 continue;
957
958 if (!DT->isReachableFromEntry(User->getParent())) {
959 U = UndefValue::get(I.getType());
960 Changed = true;
961 continue;
962 }
963
964 // The user must be a PHI node.
965 PHINode *PN = cast<PHINode>(User);
966
967 // Surprisingly, instructions can be used outside of loops without any
968 // exits. This can only happen in PHI nodes if the incoming block is
969 // unreachable.
970 BasicBlock *BB = PN->getIncomingBlock(U);
971 if (!DT->isReachableFromEntry(BB)) {
972 U = UndefValue::get(I.getType());
973 Changed = true;
974 continue;
975 }
976
977 VisitedUsers.insert(PN);
978 if (isTriviallyReplaceablePHI(*PN, I))
979 continue;
980
981 if (!canSplitPredecessors(PN, SafetyInfo))
982 return Changed;
983
984 // Split predecessors of the PHI so that we can make users trivially
985 // replaceable.
986 splitPredecessorsOfLoopExit(PN, DT, LI, CurLoop, SafetyInfo);
987
988 // Should rebuild the iterators, as they may be invalidated by
989 // splitPredecessorsOfLoopExit().
990 UI = I.user_begin();
991 UE = I.user_end();
992 }
993
994 if (VisitedUsers.empty())
995 return Changed;
996
997#ifndef NDEBUG
998 SmallVector<BasicBlock *, 32> ExitBlocks;
999 CurLoop->getUniqueExitBlocks(ExitBlocks);
1000 SmallPtrSet<BasicBlock *, 32> ExitBlockSet(ExitBlocks.begin(),
1001 ExitBlocks.end());
1002#endif
1003
1004 // Clones of this instruction. Don't create more than one per exit block!
1005 SmallDenseMap<BasicBlock *, Instruction *, 32> SunkCopies;
1006
1007 // If this instruction is only used outside of the loop, then all users are
1008 // PHI nodes in exit blocks due to LCSSA form. Just RAUW them with clones of
1009 // the instruction.
1010 SmallSetVector<User*, 8> Users(I.user_begin(), I.user_end());
1011 for (auto *UI : Users) {
1012 auto *User = cast<Instruction>(UI);
1013
1014 if (CurLoop->contains(User))
1015 continue;
1016
1017 PHINode *PN = cast<PHINode>(User);
1018 assert(ExitBlockSet.count(PN->getParent()) &&(static_cast <bool> (ExitBlockSet.count(PN->getParent
()) && "The LCSSA PHI is not in an exit block!") ? void
(0) : __assert_fail ("ExitBlockSet.count(PN->getParent()) && \"The LCSSA PHI is not in an exit block!\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 1019, __extension__ __PRETTY_FUNCTION__))
1019 "The LCSSA PHI is not in an exit block!")(static_cast <bool> (ExitBlockSet.count(PN->getParent
()) && "The LCSSA PHI is not in an exit block!") ? void
(0) : __assert_fail ("ExitBlockSet.count(PN->getParent()) && \"The LCSSA PHI is not in an exit block!\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 1019, __extension__ __PRETTY_FUNCTION__))
;
1020 // The PHI must be trivially replaceable.
1021 Instruction *New = sinkThroughTriviallyReplaceablePHI(PN, &I, LI, SunkCopies,
1022 SafetyInfo, CurLoop);
1023 PN->replaceAllUsesWith(New);
1024 PN->eraseFromParent();
1025 Changed = true;
1026 }
1027 return Changed;
1028}
1029
1030/// When an instruction is found to only use loop invariant operands that
1031/// is safe to hoist, this instruction is called to do the dirty work.
1032///
1033static bool hoist(Instruction &I, const DominatorTree *DT, const Loop *CurLoop,
1034 const LoopSafetyInfo *SafetyInfo,
1035 OptimizationRemarkEmitter *ORE) {
1036 auto *Preheader = CurLoop->getLoopPreheader();
1037 LLVM_DEBUG(dbgs() << "LICM hoisting to " << Preheader->getName() << ": " << Ido { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("licm")) { dbgs() << "LICM hoisting to " << Preheader
->getName() << ": " << I << "\n"; } } while
(false)
1038 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("licm")) { dbgs() << "LICM hoisting to " << Preheader
->getName() << ": " << I << "\n"; } } while
(false)
;
1039 ORE->emit([&]() {
1040 return OptimizationRemark(DEBUG_TYPE"licm", "Hoisted", &I) << "hoisting "
1041 << ore::NV("Inst", &I);
1042 });
1043
1044 // Metadata can be dependent on conditions we are hoisting above.
1045 // Conservatively strip all metadata on the instruction unless we were
1046 // guaranteed to execute I if we entered the loop, in which case the metadata
1047 // is valid in the loop preheader.
1048 if (I.hasMetadataOtherThanDebugLoc() &&
1049 // The check on hasMetadataOtherThanDebugLoc is to prevent us from burning
1050 // time in isGuaranteedToExecute if we don't actually have anything to
1051 // drop. It is a compile time optimization, not required for correctness.
1052 !isGuaranteedToExecute(I, DT, CurLoop, SafetyInfo))
1053 I.dropUnknownNonDebugMetadata();
1054
1055 // Move the new node to the Preheader, before its terminator.
1056 I.moveBefore(Preheader->getTerminator());
1057
1058 // Do not retain debug locations when we are moving instructions to different
1059 // basic blocks, because we want to avoid jumpy line tables. Calls, however,
1060 // need to retain their debug locs because they may be inlined.
1061 // FIXME: How do we retain source locations without causing poor debugging
1062 // behavior?
1063 if (!isa<CallInst>(I))
1064 I.setDebugLoc(DebugLoc());
1065
1066 if (isa<LoadInst>(I))
1067 ++NumMovedLoads;
1068 else if (isa<CallInst>(I))
1069 ++NumMovedCalls;
1070 ++NumHoisted;
1071 return true;
1072}
1073
1074/// Only sink or hoist an instruction if it is not a trapping instruction,
1075/// or if the instruction is known not to trap when moved to the preheader.
1076/// or if it is a trapping instruction and is guaranteed to execute.
1077static bool isSafeToExecuteUnconditionally(Instruction &Inst,
1078 const DominatorTree *DT,
1079 const Loop *CurLoop,
1080 const LoopSafetyInfo *SafetyInfo,
1081 OptimizationRemarkEmitter *ORE,
1082 const Instruction *CtxI) {
1083 if (isSafeToSpeculativelyExecute(&Inst, CtxI, DT))
22
Assuming the condition is false
23
Taking false branch
1084 return true;
1085
1086 bool GuaranteedToExecute =
1087 isGuaranteedToExecute(Inst, DT, CurLoop, SafetyInfo);
1088
1089 if (!GuaranteedToExecute) {
24
Assuming 'GuaranteedToExecute' is 0
25
Taking true branch
1090 auto *LI = dyn_cast<LoadInst>(&Inst);
1091 if (LI && CurLoop->isLoopInvariant(LI->getPointerOperand()))
26
Assuming 'LI' is non-null
27
Assuming the condition is true
28
Taking true branch
1092 ORE->emit([&]() {
29
Called C++ object pointer is null
1093 return OptimizationRemarkMissed(
1094 DEBUG_TYPE"licm", "LoadWithLoopInvariantAddressCondExecuted", LI)
1095 << "failed to hoist load with loop-invariant address "
1096 "because load is conditionally executed";
1097 });
1098 }
1099
1100 return GuaranteedToExecute;
1101}
1102
1103namespace {
1104class LoopPromoter : public LoadAndStorePromoter {
1105 Value *SomePtr; // Designated pointer to store to.
1106 const SmallSetVector<Value *, 8> &PointerMustAliases;
1107 SmallVectorImpl<BasicBlock *> &LoopExitBlocks;
1108 SmallVectorImpl<Instruction *> &LoopInsertPts;
1109 PredIteratorCache &PredCache;
1110 AliasSetTracker &AST;
1111 LoopInfo &LI;
1112 DebugLoc DL;
1113 int Alignment;
1114 bool UnorderedAtomic;
1115 AAMDNodes AATags;
1116
1117 Value *maybeInsertLCSSAPHI(Value *V, BasicBlock *BB) const {
1118 if (Instruction *I = dyn_cast<Instruction>(V))
1119 if (Loop *L = LI.getLoopFor(I->getParent()))
1120 if (!L->contains(BB)) {
1121 // We need to create an LCSSA PHI node for the incoming value and
1122 // store that.
1123 PHINode *PN = PHINode::Create(I->getType(), PredCache.size(BB),
1124 I->getName() + ".lcssa", &BB->front());
1125 for (BasicBlock *Pred : PredCache.get(BB))
1126 PN->addIncoming(I, Pred);
1127 return PN;
1128 }
1129 return V;
1130 }
1131
1132public:
1133 LoopPromoter(Value *SP, ArrayRef<const Instruction *> Insts, SSAUpdater &S,
1134 const SmallSetVector<Value *, 8> &PMA,
1135 SmallVectorImpl<BasicBlock *> &LEB,
1136 SmallVectorImpl<Instruction *> &LIP, PredIteratorCache &PIC,
1137 AliasSetTracker &ast, LoopInfo &li, DebugLoc dl, int alignment,
1138 bool UnorderedAtomic, const AAMDNodes &AATags)
1139 : LoadAndStorePromoter(Insts, S), SomePtr(SP), PointerMustAliases(PMA),
1140 LoopExitBlocks(LEB), LoopInsertPts(LIP), PredCache(PIC), AST(ast),
1141 LI(li), DL(std::move(dl)), Alignment(alignment),
1142 UnorderedAtomic(UnorderedAtomic), AATags(AATags) {}
1143
1144 bool isInstInList(Instruction *I,
1145 const SmallVectorImpl<Instruction *> &) const override {
1146 Value *Ptr;
1147 if (LoadInst *LI = dyn_cast<LoadInst>(I))
1148 Ptr = LI->getOperand(0);
1149 else
1150 Ptr = cast<StoreInst>(I)->getPointerOperand();
1151 return PointerMustAliases.count(Ptr);
1152 }
1153
1154 void doExtraRewritesBeforeFinalDeletion() const override {
1155 // Insert stores after in the loop exit blocks. Each exit block gets a
1156 // store of the live-out values that feed them. Since we've already told
1157 // the SSA updater about the defs in the loop and the preheader
1158 // definition, it is all set and we can start using it.
1159 for (unsigned i = 0, e = LoopExitBlocks.size(); i != e; ++i) {
1160 BasicBlock *ExitBlock = LoopExitBlocks[i];
1161 Value *LiveInValue = SSA.GetValueInMiddleOfBlock(ExitBlock);
1162 LiveInValue = maybeInsertLCSSAPHI(LiveInValue, ExitBlock);
1163 Value *Ptr = maybeInsertLCSSAPHI(SomePtr, ExitBlock);
1164 Instruction *InsertPos = LoopInsertPts[i];
1165 StoreInst *NewSI = new StoreInst(LiveInValue, Ptr, InsertPos);
1166 if (UnorderedAtomic)
1167 NewSI->setOrdering(AtomicOrdering::Unordered);
1168 NewSI->setAlignment(Alignment);
1169 NewSI->setDebugLoc(DL);
1170 if (AATags)
1171 NewSI->setAAMetadata(AATags);
1172 }
1173 }
1174
1175 void replaceLoadWithValue(LoadInst *LI, Value *V) const override {
1176 // Update alias analysis.
1177 AST.copyValue(LI, V);
1178 }
1179 void instructionDeleted(Instruction *I) const override { AST.deleteValue(I); }
1180};
1181
1182
1183/// Return true iff we can prove that a caller of this function can not inspect
1184/// the contents of the provided object in a well defined program.
1185bool isKnownNonEscaping(Value *Object, const TargetLibraryInfo *TLI) {
1186 if (isa<AllocaInst>(Object))
1187 // Since the alloca goes out of scope, we know the caller can't retain a
1188 // reference to it and be well defined. Thus, we don't need to check for
1189 // capture.
1190 return true;
1191
1192 // For all other objects we need to know that the caller can't possibly
1193 // have gotten a reference to the object. There are two components of
1194 // that:
1195 // 1) Object can't be escaped by this function. This is what
1196 // PointerMayBeCaptured checks.
1197 // 2) Object can't have been captured at definition site. For this, we
1198 // need to know the return value is noalias. At the moment, we use a
1199 // weaker condition and handle only AllocLikeFunctions (which are
1200 // known to be noalias). TODO
1201 return isAllocLikeFn(Object, TLI) &&
1202 !PointerMayBeCaptured(Object, true, true);
1203}
1204
1205} // namespace
1206
1207/// Try to promote memory values to scalars by sinking stores out of the
1208/// loop and moving loads to before the loop. We do this by looping over
1209/// the stores in the loop, looking for stores to Must pointers which are
1210/// loop invariant.
1211///
1212bool llvm::promoteLoopAccessesToScalars(
1213 const SmallSetVector<Value *, 8> &PointerMustAliases,
1214 SmallVectorImpl<BasicBlock *> &ExitBlocks,
1215 SmallVectorImpl<Instruction *> &InsertPts, PredIteratorCache &PIC,
1216 LoopInfo *LI, DominatorTree *DT, const TargetLibraryInfo *TLI,
1217 Loop *CurLoop, AliasSetTracker *CurAST, LoopSafetyInfo *SafetyInfo,
1218 OptimizationRemarkEmitter *ORE) {
1219 // Verify inputs.
1220 assert(LI != nullptr && DT != nullptr && CurLoop != nullptr &&(static_cast <bool> (LI != nullptr && DT != nullptr
&& CurLoop != nullptr && CurAST != nullptr &&
SafetyInfo != nullptr && "Unexpected Input to promoteLoopAccessesToScalars"
) ? void (0) : __assert_fail ("LI != nullptr && DT != nullptr && CurLoop != nullptr && CurAST != nullptr && SafetyInfo != nullptr && \"Unexpected Input to promoteLoopAccessesToScalars\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 1222, __extension__ __PRETTY_FUNCTION__))
1221 CurAST != nullptr && SafetyInfo != nullptr &&(static_cast <bool> (LI != nullptr && DT != nullptr
&& CurLoop != nullptr && CurAST != nullptr &&
SafetyInfo != nullptr && "Unexpected Input to promoteLoopAccessesToScalars"
) ? void (0) : __assert_fail ("LI != nullptr && DT != nullptr && CurLoop != nullptr && CurAST != nullptr && SafetyInfo != nullptr && \"Unexpected Input to promoteLoopAccessesToScalars\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 1222, __extension__ __PRETTY_FUNCTION__))
1222 "Unexpected Input to promoteLoopAccessesToScalars")(static_cast <bool> (LI != nullptr && DT != nullptr
&& CurLoop != nullptr && CurAST != nullptr &&
SafetyInfo != nullptr && "Unexpected Input to promoteLoopAccessesToScalars"
) ? void (0) : __assert_fail ("LI != nullptr && DT != nullptr && CurLoop != nullptr && CurAST != nullptr && SafetyInfo != nullptr && \"Unexpected Input to promoteLoopAccessesToScalars\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 1222, __extension__ __PRETTY_FUNCTION__))
;
1223
1224 Value *SomePtr = *PointerMustAliases.begin();
1225 BasicBlock *Preheader = CurLoop->getLoopPreheader();
1226
1227 // It is not safe to promote a load/store from the loop if the load/store is
1228 // conditional. For example, turning:
1229 //
1230 // for () { if (c) *P += 1; }
1231 //
1232 // into:
1233 //
1234 // tmp = *P; for () { if (c) tmp +=1; } *P = tmp;
1235 //
1236 // is not safe, because *P may only be valid to access if 'c' is true.
1237 //
1238 // The safety property divides into two parts:
1239 // p1) The memory may not be dereferenceable on entry to the loop. In this
1240 // case, we can't insert the required load in the preheader.
1241 // p2) The memory model does not allow us to insert a store along any dynamic
1242 // path which did not originally have one.
1243 //
1244 // If at least one store is guaranteed to execute, both properties are
1245 // satisfied, and promotion is legal.
1246 //
1247 // This, however, is not a necessary condition. Even if no store/load is
1248 // guaranteed to execute, we can still establish these properties.
1249 // We can establish (p1) by proving that hoisting the load into the preheader
1250 // is safe (i.e. proving dereferenceability on all paths through the loop). We
1251 // can use any access within the alias set to prove dereferenceability,
1252 // since they're all must alias.
1253 //
1254 // There are two ways establish (p2):
1255 // a) Prove the location is thread-local. In this case the memory model
1256 // requirement does not apply, and stores are safe to insert.
1257 // b) Prove a store dominates every exit block. In this case, if an exit
1258 // blocks is reached, the original dynamic path would have taken us through
1259 // the store, so inserting a store into the exit block is safe. Note that this
1260 // is different from the store being guaranteed to execute. For instance,
1261 // if an exception is thrown on the first iteration of the loop, the original
1262 // store is never executed, but the exit blocks are not executed either.
1263
1264 bool DereferenceableInPH = false;
1265 bool SafeToInsertStore = false;
1266
1267 SmallVector<Instruction *, 64> LoopUses;
1268
1269 // We start with an alignment of one and try to find instructions that allow
1270 // us to prove better alignment.
1271 unsigned Alignment = 1;
1272 // Keep track of which types of access we see
1273 bool SawUnorderedAtomic = false;
1274 bool SawNotAtomic = false;
1275 AAMDNodes AATags;
1276
1277 const DataLayout &MDL = Preheader->getModule()->getDataLayout();
1278
1279 bool IsKnownThreadLocalObject = false;
1280 if (SafetyInfo->MayThrow) {
1281 // If a loop can throw, we have to insert a store along each unwind edge.
1282 // That said, we can't actually make the unwind edge explicit. Therefore,
1283 // we have to prove that the store is dead along the unwind edge. We do
1284 // this by proving that the caller can't have a reference to the object
1285 // after return and thus can't possibly load from the object.
1286 Value *Object = GetUnderlyingObject(SomePtr, MDL);
1287 if (!isKnownNonEscaping(Object, TLI))
1288 return false;
1289 // Subtlety: Alloca's aren't visible to callers, but *are* potentially
1290 // visible to other threads if captured and used during their lifetimes.
1291 IsKnownThreadLocalObject = !isa<AllocaInst>(Object);
1292 }
1293
1294 // Check that all of the pointers in the alias set have the same type. We
1295 // cannot (yet) promote a memory location that is loaded and stored in
1296 // different sizes. While we are at it, collect alignment and AA info.
1297 for (Value *ASIV : PointerMustAliases) {
1298 // Check that all of the pointers in the alias set have the same type. We
1299 // cannot (yet) promote a memory location that is loaded and stored in
1300 // different sizes.
1301 if (SomePtr->getType() != ASIV->getType())
1302 return false;
1303
1304 for (User *U : ASIV->users()) {
1305 // Ignore instructions that are outside the loop.
1306 Instruction *UI = dyn_cast<Instruction>(U);
1307 if (!UI || !CurLoop->contains(UI))
1308 continue;
1309
1310 // If there is an non-load/store instruction in the loop, we can't promote
1311 // it.
1312 if (LoadInst *Load = dyn_cast<LoadInst>(UI)) {
1313 assert(!Load->isVolatile() && "AST broken")(static_cast <bool> (!Load->isVolatile() && "AST broken"
) ? void (0) : __assert_fail ("!Load->isVolatile() && \"AST broken\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 1313, __extension__ __PRETTY_FUNCTION__))
;
1314 if (!Load->isUnordered())
1315 return false;
1316
1317 SawUnorderedAtomic |= Load->isAtomic();
1318 SawNotAtomic |= !Load->isAtomic();
1319
1320 if (!DereferenceableInPH)
1321 DereferenceableInPH = isSafeToExecuteUnconditionally(
1322 *Load, DT, CurLoop, SafetyInfo, ORE, Preheader->getTerminator());
1323 } else if (const StoreInst *Store = dyn_cast<StoreInst>(UI)) {
1324 // Stores *of* the pointer are not interesting, only stores *to* the
1325 // pointer.
1326 if (UI->getOperand(1) != ASIV)
1327 continue;
1328 assert(!Store->isVolatile() && "AST broken")(static_cast <bool> (!Store->isVolatile() &&
"AST broken") ? void (0) : __assert_fail ("!Store->isVolatile() && \"AST broken\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 1328, __extension__ __PRETTY_FUNCTION__))
;
1329 if (!Store->isUnordered())
1330 return false;
1331
1332 SawUnorderedAtomic |= Store->isAtomic();
1333 SawNotAtomic |= !Store->isAtomic();
1334
1335 // If the store is guaranteed to execute, both properties are satisfied.
1336 // We may want to check if a store is guaranteed to execute even if we
1337 // already know that promotion is safe, since it may have higher
1338 // alignment than any other guaranteed stores, in which case we can
1339 // raise the alignment on the promoted store.
1340 unsigned InstAlignment = Store->getAlignment();
1341 if (!InstAlignment)
1342 InstAlignment =
1343 MDL.getABITypeAlignment(Store->getValueOperand()->getType());
1344
1345 if (!DereferenceableInPH || !SafeToInsertStore ||
1346 (InstAlignment > Alignment)) {
1347 if (isGuaranteedToExecute(*UI, DT, CurLoop, SafetyInfo)) {
1348 DereferenceableInPH = true;
1349 SafeToInsertStore = true;
1350 Alignment = std::max(Alignment, InstAlignment);
1351 }
1352 }
1353
1354 // If a store dominates all exit blocks, it is safe to sink.
1355 // As explained above, if an exit block was executed, a dominating
1356 // store must have been executed at least once, so we are not
1357 // introducing stores on paths that did not have them.
1358 // Note that this only looks at explicit exit blocks. If we ever
1359 // start sinking stores into unwind edges (see above), this will break.
1360 if (!SafeToInsertStore)
1361 SafeToInsertStore = llvm::all_of(ExitBlocks, [&](BasicBlock *Exit) {
1362 return DT->dominates(Store->getParent(), Exit);
1363 });
1364
1365 // If the store is not guaranteed to execute, we may still get
1366 // deref info through it.
1367 if (!DereferenceableInPH) {
1368 DereferenceableInPH = isDereferenceableAndAlignedPointer(
1369 Store->getPointerOperand(), Store->getAlignment(), MDL,
1370 Preheader->getTerminator(), DT);
1371 }
1372 } else
1373 return false; // Not a load or store.
1374
1375 // Merge the AA tags.
1376 if (LoopUses.empty()) {
1377 // On the first load/store, just take its AA tags.
1378 UI->getAAMetadata(AATags);
1379 } else if (AATags) {
1380 UI->getAAMetadata(AATags, /* Merge = */ true);
1381 }
1382
1383 LoopUses.push_back(UI);
1384 }
1385 }
1386
1387 // If we found both an unordered atomic instruction and a non-atomic memory
1388 // access, bail. We can't blindly promote non-atomic to atomic since we
1389 // might not be able to lower the result. We can't downgrade since that
1390 // would violate memory model. Also, align 0 is an error for atomics.
1391 if (SawUnorderedAtomic && SawNotAtomic)
1392 return false;
1393
1394 // If we couldn't prove we can hoist the load, bail.
1395 if (!DereferenceableInPH)
1396 return false;
1397
1398 // We know we can hoist the load, but don't have a guaranteed store.
1399 // Check whether the location is thread-local. If it is, then we can insert
1400 // stores along paths which originally didn't have them without violating the
1401 // memory model.
1402 if (!SafeToInsertStore) {
1403 if (IsKnownThreadLocalObject)
1404 SafeToInsertStore = true;
1405 else {
1406 Value *Object = GetUnderlyingObject(SomePtr, MDL);
1407 SafeToInsertStore =
1408 (isAllocLikeFn(Object, TLI) || isa<AllocaInst>(Object)) &&
1409 !PointerMayBeCaptured(Object, true, true);
1410 }
1411 }
1412
1413 // If we've still failed to prove we can sink the store, give up.
1414 if (!SafeToInsertStore)
1415 return false;
1416
1417 // Otherwise, this is safe to promote, lets do it!
1418 LLVM_DEBUG(dbgs() << "LICM: Promoting value stored to in loop: " << *SomePtrdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("licm")) { dbgs() << "LICM: Promoting value stored to in loop: "
<< *SomePtr << '\n'; } } while (false)
1419 << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("licm")) { dbgs() << "LICM: Promoting value stored to in loop: "
<< *SomePtr << '\n'; } } while (false)
;
1420 ORE->emit([&]() {
1421 return OptimizationRemark(DEBUG_TYPE"licm", "PromoteLoopAccessesToScalar",
1422 LoopUses[0])
1423 << "Moving accesses to memory location out of the loop";
1424 });
1425 ++NumPromoted;
1426
1427 // Grab a debug location for the inserted loads/stores; given that the
1428 // inserted loads/stores have little relation to the original loads/stores,
1429 // this code just arbitrarily picks a location from one, since any debug
1430 // location is better than none.
1431 DebugLoc DL = LoopUses[0]->getDebugLoc();
1432
1433 // We use the SSAUpdater interface to insert phi nodes as required.
1434 SmallVector<PHINode *, 16> NewPHIs;
1435 SSAUpdater SSA(&NewPHIs);
1436 LoopPromoter Promoter(SomePtr, LoopUses, SSA, PointerMustAliases, ExitBlocks,
1437 InsertPts, PIC, *CurAST, *LI, DL, Alignment,
1438 SawUnorderedAtomic, AATags);
1439
1440 // Set up the preheader to have a definition of the value. It is the live-out
1441 // value from the preheader that uses in the loop will use.
1442 LoadInst *PreheaderLoad = new LoadInst(
1443 SomePtr, SomePtr->getName() + ".promoted", Preheader->getTerminator());
1444 if (SawUnorderedAtomic)
1445 PreheaderLoad->setOrdering(AtomicOrdering::Unordered);
1446 PreheaderLoad->setAlignment(Alignment);
1447 PreheaderLoad->setDebugLoc(DL);
1448 if (AATags)
1449 PreheaderLoad->setAAMetadata(AATags);
1450 SSA.AddAvailableValue(Preheader, PreheaderLoad);
1451
1452 // Rewrite all the loads in the loop and remember all the definitions from
1453 // stores in the loop.
1454 Promoter.run(LoopUses);
1455
1456 // If the SSAUpdater didn't use the load in the preheader, just zap it now.
1457 if (PreheaderLoad->use_empty())
1458 PreheaderLoad->eraseFromParent();
1459
1460 return true;
1461}
1462
1463/// Returns an owning pointer to an alias set which incorporates aliasing info
1464/// from L and all subloops of L.
1465/// FIXME: In new pass manager, there is no helper function to handle loop
1466/// analysis such as cloneBasicBlockAnalysis, so the AST needs to be recomputed
1467/// from scratch for every loop. Hook up with the helper functions when
1468/// available in the new pass manager to avoid redundant computation.
1469AliasSetTracker *
1470LoopInvariantCodeMotion::collectAliasInfoForLoop(Loop *L, LoopInfo *LI,
1471 AliasAnalysis *AA) {
1472 AliasSetTracker *CurAST = nullptr;
1473 SmallVector<Loop *, 4> RecomputeLoops;
1474 for (Loop *InnerL : L->getSubLoops()) {
1475 auto MapI = LoopToAliasSetMap.find(InnerL);
1476 // If the AST for this inner loop is missing it may have been merged into
1477 // some other loop's AST and then that loop unrolled, and so we need to
1478 // recompute it.
1479 if (MapI == LoopToAliasSetMap.end()) {
1480 RecomputeLoops.push_back(InnerL);
1481 continue;
1482 }
1483 AliasSetTracker *InnerAST = MapI->second;
1484
1485 if (CurAST != nullptr) {
1486 // What if InnerLoop was modified by other passes ?
1487 CurAST->add(*InnerAST);
1488
1489 // Once we've incorporated the inner loop's AST into ours, we don't need
1490 // the subloop's anymore.
1491 delete InnerAST;
1492 } else {
1493 CurAST = InnerAST;
1494 }
1495 LoopToAliasSetMap.erase(MapI);
1496 }
1497 if (CurAST == nullptr)
1498 CurAST = new AliasSetTracker(*AA);
1499
1500 auto mergeLoop = [&](Loop *L) {
1501 // Loop over the body of this loop, looking for calls, invokes, and stores.
1502 for (BasicBlock *BB : L->blocks())
1503 CurAST->add(*BB); // Incorporate the specified basic block
1504 };
1505
1506 // Add everything from the sub loops that are no longer directly available.
1507 for (Loop *InnerL : RecomputeLoops)
1508 mergeLoop(InnerL);
1509
1510 // And merge in this loop.
1511 mergeLoop(L);
1512
1513 return CurAST;
1514}
1515
1516/// Simple analysis hook. Clone alias set info.
1517///
1518void LegacyLICMPass::cloneBasicBlockAnalysis(BasicBlock *From, BasicBlock *To,
1519 Loop *L) {
1520 AliasSetTracker *AST = LICM.getLoopToAliasSetMap().lookup(L);
1521 if (!AST)
1522 return;
1523
1524 AST->copyValue(From, To);
1525}
1526
1527/// Simple Analysis hook. Delete value V from alias set
1528///
1529void LegacyLICMPass::deleteAnalysisValue(Value *V, Loop *L) {
1530 AliasSetTracker *AST = LICM.getLoopToAliasSetMap().lookup(L);
1531 if (!AST)
1532 return;
1533
1534 AST->deleteValue(V);
1535}
1536
1537/// Simple Analysis hook. Delete value L from alias set map.
1538///
1539void LegacyLICMPass::deleteAnalysisLoop(Loop *L) {
1540 AliasSetTracker *AST = LICM.getLoopToAliasSetMap().lookup(L);
1541 if (!AST)
1542 return;
1543
1544 delete AST;
1545 LICM.getLoopToAliasSetMap().erase(L);
1546}
1547
1548/// Return true if the body of this loop may store into the memory
1549/// location pointed to by V.
1550///
1551static bool pointerInvalidatedByLoop(Value *V, uint64_t Size,
1552 const AAMDNodes &AAInfo,
1553 AliasSetTracker *CurAST) {
1554 // Check to see if any of the basic blocks in CurLoop invalidate *V.
1555 return CurAST->getAliasSetForPointer(V, Size, AAInfo).isMod();
1556}
1557
1558/// Little predicate that returns true if the specified basic block is in
1559/// a subloop of the current one, not the current one itself.
1560///
1561static bool inSubLoop(BasicBlock *BB, Loop *CurLoop, LoopInfo *LI) {
1562 assert(CurLoop->contains(BB) && "Only valid if BB is IN the loop")(static_cast <bool> (CurLoop->contains(BB) &&
"Only valid if BB is IN the loop") ? void (0) : __assert_fail
("CurLoop->contains(BB) && \"Only valid if BB is IN the loop\""
, "/build/llvm-toolchain-snapshot-7~svn337490/lib/Transforms/Scalar/LICM.cpp"
, 1562, __extension__ __PRETTY_FUNCTION__))
;
1563 return LI->getLoopFor(BB) != CurLoop;
1564}