Bug Summary

File:lib/Transforms/Scalar/ConstantHoisting.cpp
Warning:line 162, column 15
Called C++ object pointer is null

Annotated Source Code

1//===- ConstantHoisting.cpp - Prepare code for expensive constants --------===//
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 identifies expensive constants to hoist and coalesces them to
11// better prepare it for SelectionDAG-based code generation. This works around
12// the limitations of the basic-block-at-a-time approach.
13//
14// First it scans all instructions for integer constants and calculates its
15// cost. If the constant can be folded into the instruction (the cost is
16// TCC_Free) or the cost is just a simple operation (TCC_BASIC), then we don't
17// consider it expensive and leave it alone. This is the default behavior and
18// the default implementation of getIntImmCost will always return TCC_Free.
19//
20// If the cost is more than TCC_BASIC, then the integer constant can't be folded
21// into the instruction and it might be beneficial to hoist the constant.
22// Similar constants are coalesced to reduce register pressure and
23// materialization code.
24//
25// When a constant is hoisted, it is also hidden behind a bitcast to force it to
26// be live-out of the basic block. Otherwise the constant would be just
27// duplicated and each basic block would have its own copy in the SelectionDAG.
28// The SelectionDAG recognizes such constants as opaque and doesn't perform
29// certain transformations on them, which would create a new expensive constant.
30//
31// This optimization is only applied to integer constants in instructions and
32// simple (this means not nested) constant cast expressions. For example:
33// %0 = load i64* inttoptr (i64 big_constant to i64*)
34//===----------------------------------------------------------------------===//
35
36#include "llvm/Transforms/Scalar/ConstantHoisting.h"
37#include "llvm/ADT/SmallSet.h"
38#include "llvm/ADT/SmallVector.h"
39#include "llvm/ADT/Statistic.h"
40#include "llvm/IR/Constants.h"
41#include "llvm/IR/IntrinsicInst.h"
42#include "llvm/Pass.h"
43#include "llvm/Support/Debug.h"
44#include "llvm/Support/raw_ostream.h"
45#include "llvm/Transforms/Scalar.h"
46#include <tuple>
47
48using namespace llvm;
49using namespace consthoist;
50
51#define DEBUG_TYPE"consthoist" "consthoist"
52
53STATISTIC(NumConstantsHoisted, "Number of constants hoisted")static llvm::Statistic NumConstantsHoisted = {"consthoist", "NumConstantsHoisted"
, "Number of constants hoisted", {0}, false}
;
54STATISTIC(NumConstantsRebased, "Number of constants rebased")static llvm::Statistic NumConstantsRebased = {"consthoist", "NumConstantsRebased"
, "Number of constants rebased", {0}, false}
;
55
56namespace {
57/// \brief The constant hoisting pass.
58class ConstantHoistingLegacyPass : public FunctionPass {
59public:
60 static char ID; // Pass identification, replacement for typeid
61 ConstantHoistingLegacyPass() : FunctionPass(ID) {
62 initializeConstantHoistingLegacyPassPass(*PassRegistry::getPassRegistry());
63 }
64
65 bool runOnFunction(Function &Fn) override;
66
67 StringRef getPassName() const override { return "Constant Hoisting"; }
68
69 void getAnalysisUsage(AnalysisUsage &AU) const override {
70 AU.setPreservesCFG();
71 AU.addRequired<DominatorTreeWrapperPass>();
72 AU.addRequired<TargetTransformInfoWrapperPass>();
73 }
74
75 void releaseMemory() override { Impl.releaseMemory(); }
76
77private:
78 ConstantHoistingPass Impl;
79};
80}
81
82char ConstantHoistingLegacyPass::ID = 0;
83INITIALIZE_PASS_BEGIN(ConstantHoistingLegacyPass, "consthoist",static void *initializeConstantHoistingLegacyPassPassOnce(PassRegistry
&Registry) {
84 "Constant Hoisting", false, false)static void *initializeConstantHoistingLegacyPassPassOnce(PassRegistry
&Registry) {
85INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)initializeDominatorTreeWrapperPassPass(Registry);
86INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)initializeTargetTransformInfoWrapperPassPass(Registry);
87INITIALIZE_PASS_END(ConstantHoistingLegacyPass, "consthoist",PassInfo *PI = new PassInfo( "Constant Hoisting", "consthoist"
, &ConstantHoistingLegacyPass::ID, PassInfo::NormalCtor_t
(callDefaultCtor<ConstantHoistingLegacyPass>), false, false
); Registry.registerPass(*PI, true); return PI; } static once_flag
InitializeConstantHoistingLegacyPassPassFlag; void llvm::initializeConstantHoistingLegacyPassPass
(PassRegistry &Registry) { llvm::call_once(InitializeConstantHoistingLegacyPassPassFlag
, initializeConstantHoistingLegacyPassPassOnce, std::ref(Registry
)); }
88 "Constant Hoisting", false, false)PassInfo *PI = new PassInfo( "Constant Hoisting", "consthoist"
, &ConstantHoistingLegacyPass::ID, PassInfo::NormalCtor_t
(callDefaultCtor<ConstantHoistingLegacyPass>), false, false
); Registry.registerPass(*PI, true); return PI; } static once_flag
InitializeConstantHoistingLegacyPassPassFlag; void llvm::initializeConstantHoistingLegacyPassPass
(PassRegistry &Registry) { llvm::call_once(InitializeConstantHoistingLegacyPassPassFlag
, initializeConstantHoistingLegacyPassPassOnce, std::ref(Registry
)); }
89
90FunctionPass *llvm::createConstantHoistingPass() {
91 return new ConstantHoistingLegacyPass();
92}
93
94/// \brief Perform the constant hoisting optimization for the given function.
95bool ConstantHoistingLegacyPass::runOnFunction(Function &Fn) {
96 if (skipFunction(Fn))
1
Assuming the condition is false
2
Taking false branch
97 return false;
98
99 DEBUG(dbgs() << "********** Begin Constant Hoisting **********\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "********** Begin Constant Hoisting **********\n"
; } } while (false)
;
100 DEBUG(dbgs() << "********** Function: " << Fn.getName() << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "********** Function: " <<
Fn.getName() << '\n'; } } while (false)
;
101
102 bool MadeChange = Impl.runImpl(
3
Calling 'ConstantHoistingPass::runImpl'
103 Fn, getAnalysis<TargetTransformInfoWrapperPass>().getTTI(Fn),
104 getAnalysis<DominatorTreeWrapperPass>().getDomTree(), Fn.getEntryBlock());
105
106 if (MadeChange) {
107 DEBUG(dbgs() << "********** Function after Constant Hoisting: "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "********** Function after Constant Hoisting: "
<< Fn.getName() << '\n'; } } while (false)
108 << Fn.getName() << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "********** Function after Constant Hoisting: "
<< Fn.getName() << '\n'; } } while (false)
;
109 DEBUG(dbgs() << Fn)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << Fn; } } while (false)
;
110 }
111 DEBUG(dbgs() << "********** End Constant Hoisting **********\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "********** End Constant Hoisting **********\n"
; } } while (false)
;
112
113 return MadeChange;
114}
115
116
117/// \brief Find the constant materialization insertion point.
118Instruction *ConstantHoistingPass::findMatInsertPt(Instruction *Inst,
119 unsigned Idx) const {
120 // If the operand is a cast instruction, then we have to materialize the
121 // constant before the cast instruction.
122 if (Idx != ~0U) {
123 Value *Opnd = Inst->getOperand(Idx);
124 if (auto CastInst = dyn_cast<Instruction>(Opnd))
125 if (CastInst->isCast())
126 return CastInst;
127 }
128
129 // The simple and common case. This also includes constant expressions.
130 if (!isa<PHINode>(Inst) && !Inst->isEHPad())
131 return Inst;
132
133 // We can't insert directly before a phi node or an eh pad. Insert before
134 // the terminator of the incoming or dominating block.
135 assert(Entry != Inst->getParent() && "PHI or landing pad in entry block!")((Entry != Inst->getParent() && "PHI or landing pad in entry block!"
) ? static_cast<void> (0) : __assert_fail ("Entry != Inst->getParent() && \"PHI or landing pad in entry block!\""
, "/tmp/buildd/llvm-toolchain-snapshot-4.0~svn290870/lib/Transforms/Scalar/ConstantHoisting.cpp"
, 135, __PRETTY_FUNCTION__))
;
136 if (Idx != ~0U && isa<PHINode>(Inst))
137 return cast<PHINode>(Inst)->getIncomingBlock(Idx)->getTerminator();
138
139 BasicBlock *IDom = DT->getNode(Inst->getParent())->getIDom()->getBlock();
140 return IDom->getTerminator();
141}
142
143/// \brief Find an insertion point that dominates all uses.
144Instruction *ConstantHoistingPass::findConstantInsertionPoint(
145 const ConstantInfo &ConstInfo) const {
146 assert(!ConstInfo.RebasedConstants.empty() && "Invalid constant info entry.")((!ConstInfo.RebasedConstants.empty() && "Invalid constant info entry."
) ? static_cast<void> (0) : __assert_fail ("!ConstInfo.RebasedConstants.empty() && \"Invalid constant info entry.\""
, "/tmp/buildd/llvm-toolchain-snapshot-4.0~svn290870/lib/Transforms/Scalar/ConstantHoisting.cpp"
, 146, __PRETTY_FUNCTION__))
;
147 // Collect all basic blocks.
148 SmallPtrSet<BasicBlock *, 8> BBs;
149 for (auto const &RCI : ConstInfo.RebasedConstants)
14
Assuming '__begin' is equal to '__end'
150 for (auto const &U : RCI.Uses)
151 BBs.insert(findMatInsertPt(U.Inst, U.OpndIdx)->getParent());
152
153 if (BBs.count(Entry))
15
Assuming the condition is false
16
Taking false branch
154 return &Entry->front();
155
156 while (BBs.size() >= 2) {
17
Loop condition is true. Entering loop body
157 BasicBlock *BB, *BB1, *BB2;
158 BB1 = *BBs.begin();
159 BB2 = *std::next(BBs.begin());
160 BB = DT->findNearestCommonDominator(BB1, BB2);
161 if (BB == Entry)
18
Assuming pointer value is null
19
Taking true branch
162 return &Entry->front();
20
Called C++ object pointer is null
163 BBs.erase(BB1);
164 BBs.erase(BB2);
165 BBs.insert(BB);
166 }
167 assert((BBs.size() == 1) && "Expected only one element.")(((BBs.size() == 1) && "Expected only one element.") ?
static_cast<void> (0) : __assert_fail ("(BBs.size() == 1) && \"Expected only one element.\""
, "/tmp/buildd/llvm-toolchain-snapshot-4.0~svn290870/lib/Transforms/Scalar/ConstantHoisting.cpp"
, 167, __PRETTY_FUNCTION__))
;
168 Instruction &FirstInst = (*BBs.begin())->front();
169 return findMatInsertPt(&FirstInst);
170}
171
172
173/// \brief Record constant integer ConstInt for instruction Inst at operand
174/// index Idx.
175///
176/// The operand at index Idx is not necessarily the constant integer itself. It
177/// could also be a cast instruction or a constant expression that uses the
178// constant integer.
179void ConstantHoistingPass::collectConstantCandidates(
180 ConstCandMapType &ConstCandMap, Instruction *Inst, unsigned Idx,
181 ConstantInt *ConstInt) {
182 unsigned Cost;
183 // Ask the target about the cost of materializing the constant for the given
184 // instruction and operand index.
185 if (auto IntrInst = dyn_cast<IntrinsicInst>(Inst))
186 Cost = TTI->getIntImmCost(IntrInst->getIntrinsicID(), Idx,
187 ConstInt->getValue(), ConstInt->getType());
188 else
189 Cost = TTI->getIntImmCost(Inst->getOpcode(), Idx, ConstInt->getValue(),
190 ConstInt->getType());
191
192 // Ignore cheap integer constants.
193 if (Cost > TargetTransformInfo::TCC_Basic) {
194 ConstCandMapType::iterator Itr;
195 bool Inserted;
196 std::tie(Itr, Inserted) = ConstCandMap.insert(std::make_pair(ConstInt, 0));
197 if (Inserted) {
198 ConstCandVec.push_back(ConstantCandidate(ConstInt));
199 Itr->second = ConstCandVec.size() - 1;
200 }
201 ConstCandVec[Itr->second].addUser(Inst, Idx, Cost);
202 DEBUG(if (isa<ConstantInt>(Inst->getOperand(Idx)))do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { if (isa<ConstantInt>(Inst->getOperand
(Idx))) dbgs() << "Collect constant " << *ConstInt
<< " from " << *Inst << " with cost " <<
Cost << '\n'; else dbgs() << "Collect constant "
<< *ConstInt << " indirectly from " << *Inst
<< " via " << *Inst->getOperand(Idx) <<
" with cost " << Cost << '\n';; } } while (false
)
203 dbgs() << "Collect constant " << *ConstInt << " from " << *Instdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { if (isa<ConstantInt>(Inst->getOperand
(Idx))) dbgs() << "Collect constant " << *ConstInt
<< " from " << *Inst << " with cost " <<
Cost << '\n'; else dbgs() << "Collect constant "
<< *ConstInt << " indirectly from " << *Inst
<< " via " << *Inst->getOperand(Idx) <<
" with cost " << Cost << '\n';; } } while (false
)
204 << " with cost " << Cost << '\n';do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { if (isa<ConstantInt>(Inst->getOperand
(Idx))) dbgs() << "Collect constant " << *ConstInt
<< " from " << *Inst << " with cost " <<
Cost << '\n'; else dbgs() << "Collect constant "
<< *ConstInt << " indirectly from " << *Inst
<< " via " << *Inst->getOperand(Idx) <<
" with cost " << Cost << '\n';; } } while (false
)
205 elsedo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { if (isa<ConstantInt>(Inst->getOperand
(Idx))) dbgs() << "Collect constant " << *ConstInt
<< " from " << *Inst << " with cost " <<
Cost << '\n'; else dbgs() << "Collect constant "
<< *ConstInt << " indirectly from " << *Inst
<< " via " << *Inst->getOperand(Idx) <<
" with cost " << Cost << '\n';; } } while (false
)
206 dbgs() << "Collect constant " << *ConstInt << " indirectly from "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { if (isa<ConstantInt>(Inst->getOperand
(Idx))) dbgs() << "Collect constant " << *ConstInt
<< " from " << *Inst << " with cost " <<
Cost << '\n'; else dbgs() << "Collect constant "
<< *ConstInt << " indirectly from " << *Inst
<< " via " << *Inst->getOperand(Idx) <<
" with cost " << Cost << '\n';; } } while (false
)
207 << *Inst << " via " << *Inst->getOperand(Idx) << " with cost "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { if (isa<ConstantInt>(Inst->getOperand
(Idx))) dbgs() << "Collect constant " << *ConstInt
<< " from " << *Inst << " with cost " <<
Cost << '\n'; else dbgs() << "Collect constant "
<< *ConstInt << " indirectly from " << *Inst
<< " via " << *Inst->getOperand(Idx) <<
" with cost " << Cost << '\n';; } } while (false
)
208 << Cost << '\n';do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { if (isa<ConstantInt>(Inst->getOperand
(Idx))) dbgs() << "Collect constant " << *ConstInt
<< " from " << *Inst << " with cost " <<
Cost << '\n'; else dbgs() << "Collect constant "
<< *ConstInt << " indirectly from " << *Inst
<< " via " << *Inst->getOperand(Idx) <<
" with cost " << Cost << '\n';; } } while (false
)
209 )do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { if (isa<ConstantInt>(Inst->getOperand
(Idx))) dbgs() << "Collect constant " << *ConstInt
<< " from " << *Inst << " with cost " <<
Cost << '\n'; else dbgs() << "Collect constant "
<< *ConstInt << " indirectly from " << *Inst
<< " via " << *Inst->getOperand(Idx) <<
" with cost " << Cost << '\n';; } } while (false
)
;
210 }
211}
212
213/// \brief Scan the instruction for expensive integer constants and record them
214/// in the constant candidate vector.
215void ConstantHoistingPass::collectConstantCandidates(
216 ConstCandMapType &ConstCandMap, Instruction *Inst) {
217 // Skip all cast instructions. They are visited indirectly later on.
218 if (Inst->isCast())
219 return;
220
221 // Can't handle inline asm. Skip it.
222 if (auto Call = dyn_cast<CallInst>(Inst))
223 if (isa<InlineAsm>(Call->getCalledValue()))
224 return;
225
226 // Switch cases must remain constant, and if the value being tested is
227 // constant the entire thing should disappear.
228 if (isa<SwitchInst>(Inst))
229 return;
230
231 // Static allocas (constant size in the entry block) are handled by
232 // prologue/epilogue insertion so they're free anyway. We definitely don't
233 // want to make them non-constant.
234 auto AI = dyn_cast<AllocaInst>(Inst);
235 if (AI && AI->isStaticAlloca())
236 return;
237
238 // Scan all operands.
239 for (unsigned Idx = 0, E = Inst->getNumOperands(); Idx != E; ++Idx) {
240 Value *Opnd = Inst->getOperand(Idx);
241
242 // Visit constant integers.
243 if (auto ConstInt = dyn_cast<ConstantInt>(Opnd)) {
244 collectConstantCandidates(ConstCandMap, Inst, Idx, ConstInt);
245 continue;
246 }
247
248 // Visit cast instructions that have constant integers.
249 if (auto CastInst = dyn_cast<Instruction>(Opnd)) {
250 // Only visit cast instructions, which have been skipped. All other
251 // instructions should have already been visited.
252 if (!CastInst->isCast())
253 continue;
254
255 if (auto *ConstInt = dyn_cast<ConstantInt>(CastInst->getOperand(0))) {
256 // Pretend the constant is directly used by the instruction and ignore
257 // the cast instruction.
258 collectConstantCandidates(ConstCandMap, Inst, Idx, ConstInt);
259 continue;
260 }
261 }
262
263 // Visit constant expressions that have constant integers.
264 if (auto ConstExpr = dyn_cast<ConstantExpr>(Opnd)) {
265 // Only visit constant cast expressions.
266 if (!ConstExpr->isCast())
267 continue;
268
269 if (auto ConstInt = dyn_cast<ConstantInt>(ConstExpr->getOperand(0))) {
270 // Pretend the constant is directly used by the instruction and ignore
271 // the constant expression.
272 collectConstantCandidates(ConstCandMap, Inst, Idx, ConstInt);
273 continue;
274 }
275 }
276 } // end of for all operands
277}
278
279/// \brief Collect all integer constants in the function that cannot be folded
280/// into an instruction itself.
281void ConstantHoistingPass::collectConstantCandidates(Function &Fn) {
282 ConstCandMapType ConstCandMap;
283 for (BasicBlock &BB : Fn)
284 for (Instruction &Inst : BB)
285 collectConstantCandidates(ConstCandMap, &Inst);
286}
287
288// This helper function is necessary to deal with values that have different
289// bit widths (APInt Operator- does not like that). If the value cannot be
290// represented in uint64 we return an "empty" APInt. This is then interpreted
291// as the value is not in range.
292static llvm::Optional<APInt> calculateOffsetDiff(APInt V1, APInt V2)
293{
294 llvm::Optional<APInt> Res = None;
295 unsigned BW = V1.getBitWidth() > V2.getBitWidth() ?
296 V1.getBitWidth() : V2.getBitWidth();
297 uint64_t LimVal1 = V1.getLimitedValue();
298 uint64_t LimVal2 = V2.getLimitedValue();
299
300 if (LimVal1 == ~0ULL || LimVal2 == ~0ULL)
301 return Res;
302
303 uint64_t Diff = LimVal1 - LimVal2;
304 return APInt(BW, Diff, true);
305}
306
307// From a list of constants, one needs to picked as the base and the other
308// constants will be transformed into an offset from that base constant. The
309// question is which we can pick best? For example, consider these constants
310// and their number of uses:
311//
312// Constants| 2 | 4 | 12 | 42 |
313// NumUses | 3 | 2 | 8 | 7 |
314//
315// Selecting constant 12 because it has the most uses will generate negative
316// offsets for constants 2 and 4 (i.e. -10 and -8 respectively). If negative
317// offsets lead to less optimal code generation, then there might be better
318// solutions. Suppose immediates in the range of 0..35 are most optimally
319// supported by the architecture, then selecting constant 2 is most optimal
320// because this will generate offsets: 0, 2, 10, 40. Offsets 0, 2 and 10 are in
321// range 0..35, and thus 3 + 2 + 8 = 13 uses are in range. Selecting 12 would
322// have only 8 uses in range, so choosing 2 as a base is more optimal. Thus, in
323// selecting the base constant the range of the offsets is a very important
324// factor too that we take into account here. This algorithm calculates a total
325// costs for selecting a constant as the base and substract the costs if
326// immediates are out of range. It has quadratic complexity, so we call this
327// function only when we're optimising for size and there are less than 100
328// constants, we fall back to the straightforward algorithm otherwise
329// which does not do all the offset calculations.
330unsigned
331ConstantHoistingPass::maximizeConstantsInRange(ConstCandVecType::iterator S,
332 ConstCandVecType::iterator E,
333 ConstCandVecType::iterator &MaxCostItr) {
334 unsigned NumUses = 0;
335
336 if(!Entry->getParent()->optForSize() || std::distance(S,E) > 100) {
337 for (auto ConstCand = S; ConstCand != E; ++ConstCand) {
338 NumUses += ConstCand->Uses.size();
339 if (ConstCand->CumulativeCost > MaxCostItr->CumulativeCost)
340 MaxCostItr = ConstCand;
341 }
342 return NumUses;
343 }
344
345 DEBUG(dbgs() << "== Maximize constants in range ==\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "== Maximize constants in range ==\n"
; } } while (false)
;
346 int MaxCost = -1;
347 for (auto ConstCand = S; ConstCand != E; ++ConstCand) {
348 auto Value = ConstCand->ConstInt->getValue();
349 Type *Ty = ConstCand->ConstInt->getType();
350 int Cost = 0;
351 NumUses += ConstCand->Uses.size();
352 DEBUG(dbgs() << "= Constant: " << ConstCand->ConstInt->getValue() << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "= Constant: " << ConstCand
->ConstInt->getValue() << "\n"; } } while (false)
;
353
354 for (auto User : ConstCand->Uses) {
355 unsigned Opcode = User.Inst->getOpcode();
356 unsigned OpndIdx = User.OpndIdx;
357 Cost += TTI->getIntImmCost(Opcode, OpndIdx, Value, Ty);
358 DEBUG(dbgs() << "Cost: " << Cost << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "Cost: " << Cost <<
"\n"; } } while (false)
;
359
360 for (auto C2 = S; C2 != E; ++C2) {
361 llvm::Optional<APInt> Diff = calculateOffsetDiff(
362 C2->ConstInt->getValue(),
363 ConstCand->ConstInt->getValue());
364 if (Diff) {
365 const int ImmCosts =
366 TTI->getIntImmCodeSizeCost(Opcode, OpndIdx, Diff.getValue(), Ty);
367 Cost -= ImmCosts;
368 DEBUG(dbgs() << "Offset " << Diff.getValue() << " "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "Offset " << Diff.getValue
() << " " << "has penalty: " << ImmCosts <<
"\n" << "Adjusted cost: " << Cost << "\n";
} } while (false)
369 << "has penalty: " << ImmCosts << "\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "Offset " << Diff.getValue
() << " " << "has penalty: " << ImmCosts <<
"\n" << "Adjusted cost: " << Cost << "\n";
} } while (false)
370 << "Adjusted cost: " << Cost << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "Offset " << Diff.getValue
() << " " << "has penalty: " << ImmCosts <<
"\n" << "Adjusted cost: " << Cost << "\n";
} } while (false)
;
371 }
372 }
373 }
374 DEBUG(dbgs() << "Cumulative cost: " << Cost << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "Cumulative cost: " <<
Cost << "\n"; } } while (false)
;
375 if (Cost > MaxCost) {
376 MaxCost = Cost;
377 MaxCostItr = ConstCand;
378 DEBUG(dbgs() << "New candidate: " << MaxCostItr->ConstInt->getValue()do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "New candidate: " << MaxCostItr
->ConstInt->getValue() << "\n"; } } while (false)
379 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "New candidate: " << MaxCostItr
->ConstInt->getValue() << "\n"; } } while (false)
;
380 }
381 }
382 return NumUses;
383}
384
385/// \brief Find the base constant within the given range and rebase all other
386/// constants with respect to the base constant.
387void ConstantHoistingPass::findAndMakeBaseConstant(
388 ConstCandVecType::iterator S, ConstCandVecType::iterator E) {
389 auto MaxCostItr = S;
390 unsigned NumUses = maximizeConstantsInRange(S, E, MaxCostItr);
391
392 // Don't hoist constants that have only one use.
393 if (NumUses <= 1)
394 return;
395
396 ConstantInfo ConstInfo;
397 ConstInfo.BaseConstant = MaxCostItr->ConstInt;
398 Type *Ty = ConstInfo.BaseConstant->getType();
399
400 // Rebase the constants with respect to the base constant.
401 for (auto ConstCand = S; ConstCand != E; ++ConstCand) {
402 APInt Diff = ConstCand->ConstInt->getValue() -
403 ConstInfo.BaseConstant->getValue();
404 Constant *Offset = Diff == 0 ? nullptr : ConstantInt::get(Ty, Diff);
405 ConstInfo.RebasedConstants.push_back(
406 RebasedConstantInfo(std::move(ConstCand->Uses), Offset));
407 }
408 ConstantVec.push_back(std::move(ConstInfo));
409}
410
411/// \brief Finds and combines constant candidates that can be easily
412/// rematerialized with an add from a common base constant.
413void ConstantHoistingPass::findBaseConstants() {
414 // Sort the constants by value and type. This invalidates the mapping!
415 std::sort(ConstCandVec.begin(), ConstCandVec.end(),
416 [](const ConstantCandidate &LHS, const ConstantCandidate &RHS) {
417 if (LHS.ConstInt->getType() != RHS.ConstInt->getType())
418 return LHS.ConstInt->getType()->getBitWidth() <
419 RHS.ConstInt->getType()->getBitWidth();
420 return LHS.ConstInt->getValue().ult(RHS.ConstInt->getValue());
421 });
422
423 // Simple linear scan through the sorted constant candidate vector for viable
424 // merge candidates.
425 auto MinValItr = ConstCandVec.begin();
426 for (auto CC = std::next(ConstCandVec.begin()), E = ConstCandVec.end();
427 CC != E; ++CC) {
428 if (MinValItr->ConstInt->getType() == CC->ConstInt->getType()) {
429 // Check if the constant is in range of an add with immediate.
430 APInt Diff = CC->ConstInt->getValue() - MinValItr->ConstInt->getValue();
431 if ((Diff.getBitWidth() <= 64) &&
432 TTI->isLegalAddImmediate(Diff.getSExtValue()))
433 continue;
434 }
435 // We either have now a different constant type or the constant is not in
436 // range of an add with immediate anymore.
437 findAndMakeBaseConstant(MinValItr, CC);
438 // Start a new base constant search.
439 MinValItr = CC;
440 }
441 // Finalize the last base constant search.
442 findAndMakeBaseConstant(MinValItr, ConstCandVec.end());
443}
444
445/// \brief Updates the operand at Idx in instruction Inst with the result of
446/// instruction Mat. If the instruction is a PHI node then special
447/// handling for duplicate values form the same incoming basic block is
448/// required.
449/// \return The update will always succeed, but the return value indicated if
450/// Mat was used for the update or not.
451static bool updateOperand(Instruction *Inst, unsigned Idx, Instruction *Mat) {
452 if (auto PHI = dyn_cast<PHINode>(Inst)) {
453 // Check if any previous operand of the PHI node has the same incoming basic
454 // block. This is a very odd case that happens when the incoming basic block
455 // has a switch statement. In this case use the same value as the previous
456 // operand(s), otherwise we will fail verification due to different values.
457 // The values are actually the same, but the variable names are different
458 // and the verifier doesn't like that.
459 BasicBlock *IncomingBB = PHI->getIncomingBlock(Idx);
460 for (unsigned i = 0; i < Idx; ++i) {
461 if (PHI->getIncomingBlock(i) == IncomingBB) {
462 Value *IncomingVal = PHI->getIncomingValue(i);
463 Inst->setOperand(Idx, IncomingVal);
464 return false;
465 }
466 }
467 }
468
469 Inst->setOperand(Idx, Mat);
470 return true;
471}
472
473/// \brief Emit materialization code for all rebased constants and update their
474/// users.
475void ConstantHoistingPass::emitBaseConstants(Instruction *Base,
476 Constant *Offset,
477 const ConstantUser &ConstUser) {
478 Instruction *Mat = Base;
479 if (Offset) {
480 Instruction *InsertionPt = findMatInsertPt(ConstUser.Inst,
481 ConstUser.OpndIdx);
482 Mat = BinaryOperator::Create(Instruction::Add, Base, Offset,
483 "const_mat", InsertionPt);
484
485 DEBUG(dbgs() << "Materialize constant (" << *Base->getOperand(0)do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "Materialize constant (" <<
*Base->getOperand(0) << " + " << *Offset <<
") in BB " << Mat->getParent()->getName() <<
'\n' << *Mat << '\n'; } } while (false)
486 << " + " << *Offset << ") in BB "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "Materialize constant (" <<
*Base->getOperand(0) << " + " << *Offset <<
") in BB " << Mat->getParent()->getName() <<
'\n' << *Mat << '\n'; } } while (false)
487 << Mat->getParent()->getName() << '\n' << *Mat << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "Materialize constant (" <<
*Base->getOperand(0) << " + " << *Offset <<
") in BB " << Mat->getParent()->getName() <<
'\n' << *Mat << '\n'; } } while (false)
;
488 Mat->setDebugLoc(ConstUser.Inst->getDebugLoc());
489 }
490 Value *Opnd = ConstUser.Inst->getOperand(ConstUser.OpndIdx);
491
492 // Visit constant integer.
493 if (isa<ConstantInt>(Opnd)) {
494 DEBUG(dbgs() << "Update: " << *ConstUser.Inst << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "Update: " << *ConstUser
.Inst << '\n'; } } while (false)
;
495 if (!updateOperand(ConstUser.Inst, ConstUser.OpndIdx, Mat) && Offset)
496 Mat->eraseFromParent();
497 DEBUG(dbgs() << "To : " << *ConstUser.Inst << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "To : " << *ConstUser
.Inst << '\n'; } } while (false)
;
498 return;
499 }
500
501 // Visit cast instruction.
502 if (auto CastInst = dyn_cast<Instruction>(Opnd)) {
503 assert(CastInst->isCast() && "Expected an cast instruction!")((CastInst->isCast() && "Expected an cast instruction!"
) ? static_cast<void> (0) : __assert_fail ("CastInst->isCast() && \"Expected an cast instruction!\""
, "/tmp/buildd/llvm-toolchain-snapshot-4.0~svn290870/lib/Transforms/Scalar/ConstantHoisting.cpp"
, 503, __PRETTY_FUNCTION__))
;
504 // Check if we already have visited this cast instruction before to avoid
505 // unnecessary cloning.
506 Instruction *&ClonedCastInst = ClonedCastMap[CastInst];
507 if (!ClonedCastInst) {
508 ClonedCastInst = CastInst->clone();
509 ClonedCastInst->setOperand(0, Mat);
510 ClonedCastInst->insertAfter(CastInst);
511 // Use the same debug location as the original cast instruction.
512 ClonedCastInst->setDebugLoc(CastInst->getDebugLoc());
513 DEBUG(dbgs() << "Clone instruction: " << *CastInst << '\n'do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "Clone instruction: " <<
*CastInst << '\n' << "To : " <<
*ClonedCastInst << '\n'; } } while (false)
514 << "To : " << *ClonedCastInst << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "Clone instruction: " <<
*CastInst << '\n' << "To : " <<
*ClonedCastInst << '\n'; } } while (false)
;
515 }
516
517 DEBUG(dbgs() << "Update: " << *ConstUser.Inst << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "Update: " << *ConstUser
.Inst << '\n'; } } while (false)
;
518 updateOperand(ConstUser.Inst, ConstUser.OpndIdx, ClonedCastInst);
519 DEBUG(dbgs() << "To : " << *ConstUser.Inst << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "To : " << *ConstUser
.Inst << '\n'; } } while (false)
;
520 return;
521 }
522
523 // Visit constant expression.
524 if (auto ConstExpr = dyn_cast<ConstantExpr>(Opnd)) {
525 Instruction *ConstExprInst = ConstExpr->getAsInstruction();
526 ConstExprInst->setOperand(0, Mat);
527 ConstExprInst->insertBefore(findMatInsertPt(ConstUser.Inst,
528 ConstUser.OpndIdx));
529
530 // Use the same debug location as the instruction we are about to update.
531 ConstExprInst->setDebugLoc(ConstUser.Inst->getDebugLoc());
532
533 DEBUG(dbgs() << "Create instruction: " << *ConstExprInst << '\n'do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "Create instruction: " <<
*ConstExprInst << '\n' << "From : "
<< *ConstExpr << '\n'; } } while (false)
534 << "From : " << *ConstExpr << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "Create instruction: " <<
*ConstExprInst << '\n' << "From : "
<< *ConstExpr << '\n'; } } while (false)
;
535 DEBUG(dbgs() << "Update: " << *ConstUser.Inst << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "Update: " << *ConstUser
.Inst << '\n'; } } while (false)
;
536 if (!updateOperand(ConstUser.Inst, ConstUser.OpndIdx, ConstExprInst)) {
537 ConstExprInst->eraseFromParent();
538 if (Offset)
539 Mat->eraseFromParent();
540 }
541 DEBUG(dbgs() << "To : " << *ConstUser.Inst << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "To : " << *ConstUser
.Inst << '\n'; } } while (false)
;
542 return;
543 }
544}
545
546/// \brief Hoist and hide the base constant behind a bitcast and emit
547/// materialization code for derived constants.
548bool ConstantHoistingPass::emitBaseConstants() {
549 bool MadeChange = false;
550 for (auto const &ConstInfo : ConstantVec) {
8
Value assigned to field 'Entry'
9
Assuming '__begin' is not equal to '__end'
551 // Hoist and hide the base constant behind a bitcast.
552 Instruction *IP = findConstantInsertionPoint(ConstInfo);
13
Calling 'ConstantHoistingPass::findConstantInsertionPoint'
553 IntegerType *Ty = ConstInfo.BaseConstant->getType();
554 Instruction *Base =
555 new BitCastInst(ConstInfo.BaseConstant, Ty, "const", IP);
556 DEBUG(dbgs() << "Hoist constant (" << *ConstInfo.BaseConstant << ") to BB "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "Hoist constant (" <<
*ConstInfo.BaseConstant << ") to BB " << IP->
getParent()->getName() << '\n' << *Base <<
'\n'; } } while (false)
557 << IP->getParent()->getName() << '\n' << *Base << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("consthoist")) { dbgs() << "Hoist constant (" <<
*ConstInfo.BaseConstant << ") to BB " << IP->
getParent()->getName() << '\n' << *Base <<
'\n'; } } while (false)
;
558 NumConstantsHoisted++;
559
560 // Emit materialization code for all rebased constants.
561 for (auto const &RCI : ConstInfo.RebasedConstants) {
10
Assuming '__begin' is equal to '__end'
11
Assuming '__begin' is equal to '__end'
12
Assuming '__begin' is equal to '__end'
562 NumConstantsRebased++;
563 for (auto const &U : RCI.Uses)
564 emitBaseConstants(Base, RCI.Offset, U);
565 }
566
567 // Use the same debug location as the last user of the constant.
568 assert(!Base->use_empty() && "The use list is empty!?")((!Base->use_empty() && "The use list is empty!?")
? static_cast<void> (0) : __assert_fail ("!Base->use_empty() && \"The use list is empty!?\""
, "/tmp/buildd/llvm-toolchain-snapshot-4.0~svn290870/lib/Transforms/Scalar/ConstantHoisting.cpp"
, 568, __PRETTY_FUNCTION__))
;
569 assert(isa<Instruction>(Base->user_back()) &&((isa<Instruction>(Base->user_back()) && "All uses should be instructions."
) ? static_cast<void> (0) : __assert_fail ("isa<Instruction>(Base->user_back()) && \"All uses should be instructions.\""
, "/tmp/buildd/llvm-toolchain-snapshot-4.0~svn290870/lib/Transforms/Scalar/ConstantHoisting.cpp"
, 570, __PRETTY_FUNCTION__))
570 "All uses should be instructions.")((isa<Instruction>(Base->user_back()) && "All uses should be instructions."
) ? static_cast<void> (0) : __assert_fail ("isa<Instruction>(Base->user_back()) && \"All uses should be instructions.\""
, "/tmp/buildd/llvm-toolchain-snapshot-4.0~svn290870/lib/Transforms/Scalar/ConstantHoisting.cpp"
, 570, __PRETTY_FUNCTION__))
;
571 Base->setDebugLoc(cast<Instruction>(Base->user_back())->getDebugLoc());
572
573 // Correct for base constant, which we counted above too.
574 NumConstantsRebased--;
575 MadeChange = true;
576 }
577 return MadeChange;
578}
579
580/// \brief Check all cast instructions we made a copy of and remove them if they
581/// have no more users.
582void ConstantHoistingPass::deleteDeadCastInst() const {
583 for (auto const &I : ClonedCastMap)
584 if (I.first->use_empty())
585 I.first->eraseFromParent();
586}
587
588/// \brief Optimize expensive integer constants in the given function.
589bool ConstantHoistingPass::runImpl(Function &Fn, TargetTransformInfo &TTI,
590 DominatorTree &DT, BasicBlock &Entry) {
591 this->TTI = &TTI;
592 this->DT = &DT;
593 this->Entry = &Entry;
594 // Collect all constant candidates.
595 collectConstantCandidates(Fn);
596
597 // There are no constant candidates to worry about.
598 if (ConstCandVec.empty())
4
Assuming the condition is false
5
Taking false branch
599 return false;
600
601 // Combine constants that can be easily materialized with an add from a common
602 // base constant.
603 findBaseConstants();
604
605 // There are no constants to emit.
606 if (ConstantVec.empty())
6
Taking false branch
607 return false;
608
609 // Finally hoist the base constant and emit materialization code for dependent
610 // constants.
611 bool MadeChange = emitBaseConstants();
7
Calling 'ConstantHoistingPass::emitBaseConstants'
612
613 // Cleanup dead instructions.
614 deleteDeadCastInst();
615
616 return MadeChange;
617}
618
619PreservedAnalyses ConstantHoistingPass::run(Function &F,
620 FunctionAnalysisManager &AM) {
621 auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
622 auto &TTI = AM.getResult<TargetIRAnalysis>(F);
623 if (!runImpl(F, TTI, DT, F.getEntryBlock()))
624 return PreservedAnalyses::all();
625
626 // FIXME: This should also 'preserve the CFG'.
627 return PreservedAnalyses::none();
628}