Bug Summary

File:llvm/lib/Transforms/Scalar/LoopDeletion.cpp
Warning:line 66, column 23
Called C++ object pointer is null

Annotated Source Code

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clang -cc1 -cc1 -triple x86_64-pc-linux-gnu -analyze -disable-free -disable-llvm-verifier -discard-value-names -main-file-name LoopDeletion.cpp -analyzer-store=region -analyzer-opt-analyze-nested-blocks -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 -setup-static-analyzer -analyzer-config-compatibility-mode=true -mrelocation-model pic -pic-level 2 -fhalf-no-semantic-interposition -mframe-pointer=none -fmath-errno -fno-rounding-math -mconstructor-aliases -munwind-tables -target-cpu x86-64 -tune-cpu generic -debugger-tuning=gdb -ffunction-sections -fdata-sections -fcoverage-compilation-dir=/build/llvm-toolchain-snapshot-13~++20210413100635+64c24f493e5f/build-llvm/lib/Transforms/Scalar -resource-dir /usr/lib/llvm-13/lib/clang/13.0.0 -D _DEBUG -D _GNU_SOURCE -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D __STDC_LIMIT_MACROS -I /build/llvm-toolchain-snapshot-13~++20210413100635+64c24f493e5f/build-llvm/lib/Transforms/Scalar -I /build/llvm-toolchain-snapshot-13~++20210413100635+64c24f493e5f/llvm/lib/Transforms/Scalar -I /build/llvm-toolchain-snapshot-13~++20210413100635+64c24f493e5f/build-llvm/include -I /build/llvm-toolchain-snapshot-13~++20210413100635+64c24f493e5f/llvm/include -U NDEBUG -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/c++/6.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/x86_64-linux-gnu/c++/6.3.0 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../include/c++/6.3.0/backward -internal-isystem /usr/lib/llvm-13/lib/clang/13.0.0/include -internal-isystem /usr/local/include -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/6.3.0/../../../../x86_64-linux-gnu/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++14 -fdeprecated-macro -fdebug-compilation-dir=/build/llvm-toolchain-snapshot-13~++20210413100635+64c24f493e5f/build-llvm/lib/Transforms/Scalar -fdebug-prefix-map=/build/llvm-toolchain-snapshot-13~++20210413100635+64c24f493e5f=. -ferror-limit 19 -fvisibility-inlines-hidden -stack-protector 2 -fgnuc-version=4.2.1 -vectorize-loops -vectorize-slp -analyzer-output=html -analyzer-config stable-report-filename=true -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o /tmp/scan-build-2021-04-14-063029-18377-1 -x c++ /build/llvm-toolchain-snapshot-13~++20210413100635+64c24f493e5f/llvm/lib/Transforms/Scalar/LoopDeletion.cpp
1//===- LoopDeletion.cpp - Dead Loop Deletion Pass ---------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file implements the Dead Loop Deletion Pass. This pass is responsible
10// for eliminating loops with non-infinite computable trip counts that have no
11// side effects or volatile instructions, and do not contribute to the
12// computation of the function's return value.
13//
14//===----------------------------------------------------------------------===//
15
16#include "llvm/Transforms/Scalar/LoopDeletion.h"
17#include "llvm/ADT/SmallVector.h"
18#include "llvm/ADT/Statistic.h"
19#include "llvm/Analysis/GlobalsModRef.h"
20#include "llvm/Analysis/LoopPass.h"
21#include "llvm/Analysis/MemorySSA.h"
22#include "llvm/Analysis/OptimizationRemarkEmitter.h"
23#include "llvm/IR/Dominators.h"
24#include "llvm/IR/PatternMatch.h"
25#include "llvm/InitializePasses.h"
26#include "llvm/Transforms/Scalar.h"
27#include "llvm/Transforms/Scalar/LoopPassManager.h"
28#include "llvm/Transforms/Utils/LoopUtils.h"
29
30using namespace llvm;
31
32#define DEBUG_TYPE"loop-delete" "loop-delete"
33
34STATISTIC(NumDeleted, "Number of loops deleted")static llvm::Statistic NumDeleted = {"loop-delete", "NumDeleted"
, "Number of loops deleted"};
35
36enum class LoopDeletionResult {
37 Unmodified,
38 Modified,
39 Deleted,
40};
41
42static LoopDeletionResult merge(LoopDeletionResult A, LoopDeletionResult B) {
43 if (A == LoopDeletionResult::Deleted || B == LoopDeletionResult::Deleted)
44 return LoopDeletionResult::Deleted;
45 if (A == LoopDeletionResult::Modified || B == LoopDeletionResult::Modified)
46 return LoopDeletionResult::Modified;
47 return LoopDeletionResult::Unmodified;
48}
49
50/// Determines if a loop is dead.
51///
52/// This assumes that we've already checked for unique exit and exiting blocks,
53/// and that the code is in LCSSA form.
54static bool isLoopDead(Loop *L, ScalarEvolution &SE,
55 SmallVectorImpl<BasicBlock *> &ExitingBlocks,
56 BasicBlock *ExitBlock, bool &Changed,
57 BasicBlock *Preheader) {
58 // Make sure that all PHI entries coming from the loop are loop invariant.
59 // Because the code is in LCSSA form, any values used outside of the loop
60 // must pass through a PHI in the exit block, meaning that this check is
61 // sufficient to guarantee that no loop-variant values are used outside
62 // of the loop.
63 bool AllEntriesInvariant = true;
64 bool AllOutgoingValuesSame = true;
65 if (!L->hasNoExitBlocks()) {
19
←
Assuming the condition is true
→
20
←
Taking true branch
→
66 for (PHINode &P : ExitBlock->phis()) {
21
←
Called C++ object pointer is null
67 Value *incoming = P.getIncomingValueForBlock(ExitingBlocks[0]);
68
69 // Make sure all exiting blocks produce the same incoming value for the
70 // block. If there are different incoming values for different exiting
71 // blocks, then it is impossible to statically determine which value
72 // should be used.
73 AllOutgoingValuesSame =
74 all_of(makeArrayRef(ExitingBlocks).slice(1), [&](BasicBlock *BB) {
75 return incoming == P.getIncomingValueForBlock(BB);
76 });
77
78 if (!AllOutgoingValuesSame)
79 break;
80
81 if (Instruction *I = dyn_cast<Instruction>(incoming))
82 if (!L->makeLoopInvariant(I, Changed, Preheader->getTerminator())) {
83 AllEntriesInvariant = false;
84 break;
85 }
86 }
87 }
88
89 if (Changed)
90 SE.forgetLoopDispositions(L);
91
92 if (!AllEntriesInvariant || !AllOutgoingValuesSame)
93 return false;
94
95 // Make sure that no instructions in the block have potential side-effects.
96 // This includes instructions that could write to memory, and loads that are
97 // marked volatile.
98 for (auto &I : L->blocks())
99 if (any_of(*I, [](Instruction &I) {
100 return I.mayHaveSideEffects() && !I.isDroppable();
101 }))
102 return false;
103 return true;
104}
105
106/// This function returns true if there is no viable path from the
107/// entry block to the header of \p L. Right now, it only does
108/// a local search to save compile time.
109static bool isLoopNeverExecuted(Loop *L) {
110 using namespace PatternMatch;
111
112 auto *Preheader = L->getLoopPreheader();
113 // TODO: We can relax this constraint, since we just need a loop
114 // predecessor.
115 assert(Preheader && "Needs preheader!")((Preheader && "Needs preheader!") ? static_cast<void
> (0) : __assert_fail ("Preheader && \"Needs preheader!\""
, "/build/llvm-toolchain-snapshot-13~++20210413100635+64c24f493e5f/llvm/lib/Transforms/Scalar/LoopDeletion.cpp"
, 115, __PRETTY_FUNCTION__));
116
117 if (Preheader == &Preheader->getParent()->getEntryBlock())
118 return false;
119 // All predecessors of the preheader should have a constant conditional
120 // branch, with the loop's preheader as not-taken.
121 for (auto *Pred: predecessors(Preheader)) {
122 BasicBlock *Taken, *NotTaken;
123 ConstantInt *Cond;
124 if (!match(Pred->getTerminator(),
125 m_Br(m_ConstantInt(Cond), Taken, NotTaken)))
126 return false;
127 if (!Cond->getZExtValue())
128 std::swap(Taken, NotTaken);
129 if (Taken == Preheader)
130 return false;
131 }
132 assert(!pred_empty(Preheader) &&((!pred_empty(Preheader) && "Preheader should have predecessors at this point!"
) ? static_cast<void> (0) : __assert_fail ("!pred_empty(Preheader) && \"Preheader should have predecessors at this point!\""
, "/build/llvm-toolchain-snapshot-13~++20210413100635+64c24f493e5f/llvm/lib/Transforms/Scalar/LoopDeletion.cpp"
, 133, __PRETTY_FUNCTION__))
133 "Preheader should have predecessors at this point!")((!pred_empty(Preheader) && "Preheader should have predecessors at this point!"
) ? static_cast<void> (0) : __assert_fail ("!pred_empty(Preheader) && \"Preheader should have predecessors at this point!\""
, "/build/llvm-toolchain-snapshot-13~++20210413100635+64c24f493e5f/llvm/lib/Transforms/Scalar/LoopDeletion.cpp"
, 133, __PRETTY_FUNCTION__));
134 // All the predecessors have the loop preheader as not-taken target.
135 return true;
136}
137
138/// If we can prove the backedge is untaken, remove it. This destroys the
139/// loop, but leaves the (now trivially loop invariant) control flow and
140/// side effects (if any) in place.
141static LoopDeletionResult
142breakBackedgeIfNotTaken(Loop *L, DominatorTree &DT, ScalarEvolution &SE,
143 LoopInfo &LI, MemorySSA *MSSA,
144 OptimizationRemarkEmitter &ORE) {
145 assert(L->isLCSSAForm(DT) && "Expected LCSSA!")((L->isLCSSAForm(DT) && "Expected LCSSA!") ? static_cast
<void> (0) : __assert_fail ("L->isLCSSAForm(DT) && \"Expected LCSSA!\""
, "/build/llvm-toolchain-snapshot-13~++20210413100635+64c24f493e5f/llvm/lib/Transforms/Scalar/LoopDeletion.cpp"
, 145, __PRETTY_FUNCTION__));
146
147 if (!L->getLoopLatch())
148 return LoopDeletionResult::Unmodified;
149
150 auto *BTC = SE.getBackedgeTakenCount(L);
151 if (!BTC->isZero())
152 return LoopDeletionResult::Unmodified;
153
154 breakLoopBackedge(L, DT, SE, LI, MSSA);
155 return LoopDeletionResult::Deleted;
156}
157
158/// Remove a loop if it is dead.
159///
160/// A loop is considered dead either if it does not impact the observable
161/// behavior of the program other than finite running time, or if it is
162/// required to make progress by an attribute such as 'mustprogress' or
163/// 'llvm.loop.mustprogress' and does not make any. This may remove
164/// infinite loops that have been required to make progress.
165///
166/// This entire process relies pretty heavily on LoopSimplify form and LCSSA in
167/// order to make various safety checks work.
168///
169/// \returns true if any changes were made. This may mutate the loop even if it
170/// is unable to delete it due to hoisting trivially loop invariant
171/// instructions out of the loop.
172static LoopDeletionResult deleteLoopIfDead(Loop *L, DominatorTree &DT,
173 ScalarEvolution &SE, LoopInfo &LI,
174 MemorySSA *MSSA,
175 OptimizationRemarkEmitter &ORE) {
176 assert(L->isLCSSAForm(DT) && "Expected LCSSA!")((L->isLCSSAForm(DT) && "Expected LCSSA!") ? static_cast
<void> (0) : __assert_fail ("L->isLCSSAForm(DT) && \"Expected LCSSA!\""
, "/build/llvm-toolchain-snapshot-13~++20210413100635+64c24f493e5f/llvm/lib/Transforms/Scalar/LoopDeletion.cpp"
, 176, __PRETTY_FUNCTION__));
8
←
Assuming the condition is true
→
9
←
'?' condition is true
→
177
178 // We can only remove the loop if there is a preheader that we can branch from
179 // after removing it. Also, if LoopSimplify form is not available, stay out
180 // of trouble.
181 BasicBlock *Preheader = L->getLoopPreheader();
182 if (!Preheader || !L->hasDedicatedExits()) {
10
←
Assuming 'Preheader' is non-null
→
11
←
Assuming the condition is false
→
12
←
Taking false branch
→
183 LLVM_DEBUG(do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-delete")) { dbgs() << "Deletion requires Loop with preheader and dedicated exits.\n"
; } } while (false)
184 dbgs()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-delete")) { dbgs() << "Deletion requires Loop with preheader and dedicated exits.\n"
; } } while (false)
185 << "Deletion requires Loop with preheader and dedicated exits.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-delete")) { dbgs() << "Deletion requires Loop with preheader and dedicated exits.\n"
; } } while (false);
186 return LoopDeletionResult::Unmodified;
187 }
188
189 BasicBlock *ExitBlock = L->getUniqueExitBlock();
13
←
'ExitBlock' initialized here
→
190
191 if (ExitBlock && isLoopNeverExecuted(L)) {
14
←
Assuming 'ExitBlock' is null
→
192 LLVM_DEBUG(dbgs() << "Loop is proven to never execute, delete it!")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-delete")) { dbgs() << "Loop is proven to never execute, delete it!"
; } } while (false);
193 // We need to forget the loop before setting the incoming values of the exit
194 // phis to undef, so we properly invalidate the SCEV expressions for those
195 // phis.
196 SE.forgetLoop(L);
197 // Set incoming value to undef for phi nodes in the exit block.
198 for (PHINode &P : ExitBlock->phis()) {
199 std::fill(P.incoming_values().begin(), P.incoming_values().end(),
200 UndefValue::get(P.getType()));
201 }
202 ORE.emit([&]() {
203 return OptimizationRemark(DEBUG_TYPE"loop-delete", "NeverExecutes", L->getStartLoc(),
204 L->getHeader())
205 << "Loop deleted because it never executes";
206 });
207 deleteDeadLoop(L, &DT, &SE, &LI, MSSA);
208 ++NumDeleted;
209 return LoopDeletionResult::Deleted;
210 }
211
212 // The remaining checks below are for a loop being dead because all statements
213 // in the loop are invariant.
214 SmallVector<BasicBlock *, 4> ExitingBlocks;
215 L->getExitingBlocks(ExitingBlocks);
216
217 // We require that the loop has at most one exit block. Otherwise, we'd be in
218 // the situation of needing to be able to solve statically which exit block
219 // will be branched to, or trying to preserve the branching logic in a loop
220 // invariant manner.
221 if (!ExitBlock
14.1
'ExitBlock' is null
 && !L->hasNoExitBlocks()) {
15
←
Assuming the condition is false
→
16
←
Taking false branch
→
222 LLVM_DEBUG(dbgs() << "Deletion requires at most one exit block.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-delete")) { dbgs() << "Deletion requires at most one exit block.\n"
; } } while (false);
223 return LoopDeletionResult::Unmodified;
224 }
225 // Finally, we have to check that the loop really is dead.
226 bool Changed = false;
227 if (!isLoopDead(L, SE, ExitingBlocks, ExitBlock, Changed, Preheader)) {
17
←
Passing null pointer value via 4th parameter 'ExitBlock'
→
18
←
Calling 'isLoopDead'
→
228 LLVM_DEBUG(dbgs() << "Loop is not invariant, cannot delete.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-delete")) { dbgs() << "Loop is not invariant, cannot delete.\n"
; } } while (false);
229 return Changed ? LoopDeletionResult::Modified
230 : LoopDeletionResult::Unmodified;
231 }
232
233 // Don't remove loops for which we can't solve the trip count unless the loop
234 // was required to make progress but has been determined to be dead.
235 const SCEV *S = SE.getConstantMaxBackedgeTakenCount(L);
236 if (isa<SCEVCouldNotCompute>(S) &&
237 !L->getHeader()->getParent()->mustProgress() && !hasMustProgress(L)) {
238 LLVM_DEBUG(dbgs() << "Could not compute SCEV MaxBackedgeTakenCount and was "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-delete")) { dbgs() << "Could not compute SCEV MaxBackedgeTakenCount and was "
"not required to make progress.\n"; } } while (false)
239 "not required to make progress.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-delete")) { dbgs() << "Could not compute SCEV MaxBackedgeTakenCount and was "
"not required to make progress.\n"; } } while (false);
240 return Changed ? LoopDeletionResult::Modified
241 : LoopDeletionResult::Unmodified;
242 }
243
244 LLVM_DEBUG(dbgs() << "Loop is invariant, delete it!")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-delete")) { dbgs() << "Loop is invariant, delete it!"
; } } while (false);
245 ORE.emit([&]() {
246 return OptimizationRemark(DEBUG_TYPE"loop-delete", "Invariant", L->getStartLoc(),
247 L->getHeader())
248 << "Loop deleted because it is invariant";
249 });
250 deleteDeadLoop(L, &DT, &SE, &LI, MSSA);
251 ++NumDeleted;
252
253 return LoopDeletionResult::Deleted;
254}
255
256PreservedAnalyses LoopDeletionPass::run(Loop &L, LoopAnalysisManager &AM,
257 LoopStandardAnalysisResults &AR,
258 LPMUpdater &Updater) {
259
260 LLVM_DEBUG(dbgs() << "Analyzing Loop for deletion: ")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-delete")) { dbgs() << "Analyzing Loop for deletion: "
; } } while (false);
261 LLVM_DEBUG(L.dump())do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-delete")) { L.dump(); } } while (false);
262 std::string LoopName = std::string(L.getName());
263 // For the new PM, we can't use OptimizationRemarkEmitter as an analysis
264 // pass. Function analyses need to be preserved across loop transformations
265 // but ORE cannot be preserved (see comment before the pass definition).
266 OptimizationRemarkEmitter ORE(L.getHeader()->getParent());
267 auto Result = deleteLoopIfDead(&L, AR.DT, AR.SE, AR.LI, AR.MSSA, ORE);
268
269 // If we can prove the backedge isn't taken, just break it and be done. This
270 // leaves the loop structure in place which means it can handle dispatching
271 // to the right exit based on whatever loop invariant structure remains.
272 if (Result != LoopDeletionResult::Deleted)
273 Result = merge(Result, breakBackedgeIfNotTaken(&L, AR.DT, AR.SE, AR.LI,
274 AR.MSSA, ORE));
275
276 if (Result == LoopDeletionResult::Unmodified)
277 return PreservedAnalyses::all();
278
279 if (Result == LoopDeletionResult::Deleted)
280 Updater.markLoopAsDeleted(L, LoopName);
281
282 auto PA = getLoopPassPreservedAnalyses();
283 if (AR.MSSA)
284 PA.preserve<MemorySSAAnalysis>();
285 return PA;
286}
287
288namespace {
289class LoopDeletionLegacyPass : public LoopPass {
290public:
291 static char ID; // Pass ID, replacement for typeid
292 LoopDeletionLegacyPass() : LoopPass(ID) {
293 initializeLoopDeletionLegacyPassPass(*PassRegistry::getPassRegistry());
294 }
295
296 // Possibly eliminate loop L if it is dead.
297 bool runOnLoop(Loop *L, LPPassManager &) override;
298
299 void getAnalysisUsage(AnalysisUsage &AU) const override {
300 AU.addPreserved<MemorySSAWrapperPass>();
301 getLoopAnalysisUsage(AU);
302 }
303};
304}
305
306char LoopDeletionLegacyPass::ID = 0;
307INITIALIZE_PASS_BEGIN(LoopDeletionLegacyPass, "loop-deletion",static void *initializeLoopDeletionLegacyPassPassOnce(PassRegistry
&Registry) {
308 "Delete dead loops", false, false)static void *initializeLoopDeletionLegacyPassPassOnce(PassRegistry
&Registry) {
309INITIALIZE_PASS_DEPENDENCY(LoopPass)initializeLoopPassPass(Registry);
310INITIALIZE_PASS_END(LoopDeletionLegacyPass, "loop-deletion",PassInfo *PI = new PassInfo( "Delete dead loops", "loop-deletion"
, &LoopDeletionLegacyPass::ID, PassInfo::NormalCtor_t(callDefaultCtor
<LoopDeletionLegacyPass>), false, false); Registry.registerPass
(*PI, true); return PI; } static llvm::once_flag InitializeLoopDeletionLegacyPassPassFlag
; void llvm::initializeLoopDeletionLegacyPassPass(PassRegistry
&Registry) { llvm::call_once(InitializeLoopDeletionLegacyPassPassFlag
, initializeLoopDeletionLegacyPassPassOnce, std::ref(Registry
)); }
311 "Delete dead loops", false, false)PassInfo *PI = new PassInfo( "Delete dead loops", "loop-deletion"
, &LoopDeletionLegacyPass::ID, PassInfo::NormalCtor_t(callDefaultCtor
<LoopDeletionLegacyPass>), false, false); Registry.registerPass
(*PI, true); return PI; } static llvm::once_flag InitializeLoopDeletionLegacyPassPassFlag
; void llvm::initializeLoopDeletionLegacyPassPass(PassRegistry
&Registry) { llvm::call_once(InitializeLoopDeletionLegacyPassPassFlag
, initializeLoopDeletionLegacyPassPassOnce, std::ref(Registry
)); }
312
313Pass *llvm::createLoopDeletionPass() { return new LoopDeletionLegacyPass(); }
314
315bool LoopDeletionLegacyPass::runOnLoop(Loop *L, LPPassManager &LPM) {
316 if (skipLoop(L))
1
Assuming the condition is false
→
2
←
Taking false branch
→
317 return false;
318 DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
319 ScalarEvolution &SE = getAnalysis<ScalarEvolutionWrapperPass>().getSE();
320 LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
321 auto *MSSAAnalysis = getAnalysisIfAvailable<MemorySSAWrapperPass>();
322 MemorySSA *MSSA = nullptr;
323 if (MSSAAnalysis
2.1
'MSSAAnalysis' is null
)
3
←
Taking false branch
→
324 MSSA = &MSSAAnalysis->getMSSA();
325 // For the old PM, we can't use OptimizationRemarkEmitter as an analysis
326 // pass. Function analyses need to be preserved across loop transformations
327 // but ORE cannot be preserved (see comment before the pass definition).
328 OptimizationRemarkEmitter ORE(L->getHeader()->getParent());
329
330 LLVM_DEBUG(dbgs() << "Analyzing Loop for deletion: ")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-delete")) { dbgs() << "Analyzing Loop for deletion: "
; } } while (false);
4
←
Assuming 'DebugFlag' is false
→
5
←
Loop condition is false. Exiting loop
→
331 LLVM_DEBUG(L->dump())do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("loop-delete")) { L->dump(); } } while (false);
6
←
Loop condition is false. Exiting loop
→
332
333 LoopDeletionResult Result = deleteLoopIfDead(L, DT, SE, LI, MSSA, ORE);
7
←
Calling 'deleteLoopIfDead'
→
334
335 // If we can prove the backedge isn't taken, just break it and be done. This
336 // leaves the loop structure in place which means it can handle dispatching
337 // to the right exit based on whatever loop invariant structure remains.
338 if (Result != LoopDeletionResult::Deleted)
339 Result = merge(Result, breakBackedgeIfNotTaken(L, DT, SE, LI, MSSA, ORE));
340
341 if (Result == LoopDeletionResult::Deleted)
342 LPM.markLoopAsDeleted(*L);
343
344 return Result != LoopDeletionResult::Unmodified;
345}