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[SCEV] Do not cache S -> V if S is not equivalent of V

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SCEV tracks the correspondence of created SCEV to original instruction.
However during creation of SCEV it is possible that nuw/nsw/exact flags are
lost.

As a result during expansion of the SCEV the instruction with nuw/nsw/exact
will be used where it was expected and we produce poison incorreclty.

Reviewers: sanjoy, mkazantsev, sebpop, jbhateja
Reviewed By: sanjoy
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D41578

llvm-svn: 322058
This commit is contained in:
Serguei Katkov 2018-01-09 06:47:14 +00:00
parent 3e7f820f40
commit d58a989008
3 changed files with 124 additions and 3 deletions
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20
lib/Analysis/ScalarEvolution.cpp
View File

@ -3774,6 +3774,24 @@ void ScalarEvolution::eraseValueFromMap(Value *V) {
}
}
/// Check whether value has nuw/nsw/exact set but SCEV does not.
/// TODO: In reality it is better to check the poison recursevely
/// but this is better than nothing.
static bool SCEVLostPoisonFlags(const SCEV *S, const Value *V) {
if (auto *I = dyn_cast<Instruction>(V)) {
if (isa<OverflowingBinaryOperator>(I)) {
if (auto *NS = dyn_cast<SCEVNAryExpr>(S)) {
if (I->hasNoSignedWrap() && !NS->hasNoSignedWrap())
return true;
if (I->hasNoUnsignedWrap() && !NS->hasNoUnsignedWrap())
return true;
}
} else if (isa<PossiblyExactOperator>(I) && I->isExact())
return true;
}
return false;
}
/// Return an existing SCEV if it exists, otherwise analyze the expression and
/// create a new one.
const SCEV *ScalarEvolution::getSCEV(Value *V) {
@ -3787,7 +3805,7 @@ const SCEV *ScalarEvolution::getSCEV(Value *V) {
// ValueExprMap before insert S->{V, 0} into ExprValueMap.
std::pair<ValueExprMapType::iterator, bool> Pair =
ValueExprMap.insert({SCEVCallbackVH(V, this), S});
if (Pair.second) {
if (Pair.second && !SCEVLostPoisonFlags(S, V)) {
ExprValueMap[S].insert({V, nullptr});
// If S == Stripped + Offset, add Stripped -> {V, Offset} into

5
test/Transforms/LoopStrengthReduce/post-inc-icmpzero.ll
View File

@ -6,11 +6,12 @@
; CHECK: [[r1:%[a-z0-9\.]+]] = sub i64 %sub.ptr.lhs.cast, %sub.ptr.rhs.cast
; CHECK: [[r2:%[a-z0-9\.]+]] = lshr exact i64 [[r1]], 1
; CHECK: [[r3:%[a-z0-9\.]+]] = bitcast i64 [[r2]] to i64
; CHECK: for.body.lr.ph:
; CHECK: [[r3:%[a-z0-9]+]] = shl i64 [[r2]], 1
; CHECK: [[r4:%[a-z0-9]+]] = shl i64 [[r3]], 1
; CHECK: br label %for.body
; CHECK: for.body:
; CHECK: %lsr.iv2 = phi i64 [ %lsr.iv.next, %for.body ], [ [[r3]], %for.body.lr.ph ]
; CHECK: %lsr.iv2 = phi i64 [ %lsr.iv.next, %for.body ], [ [[r4]], %for.body.lr.ph ]
; CHECK: %lsr.iv.next = add i64 %lsr.iv2, -2
; CHECK: %lsr.iv.next3 = inttoptr i64 %lsr.iv.next to i16*
; CHECK: %cmp27 = icmp eq i16* %lsr.iv.next3, null

102
unittests/Analysis/ScalarEvolutionTest.cpp
View File

@ -1288,5 +1288,107 @@ TEST_F(ScalarEvolutionsTest, SCEVExpanderNSW) {
EXPECT_FALSE(I->hasNoSignedWrap());
}
// Check that SCEV does not save the SCEV -> V
// mapping of SCEV differ from V in NUW flag.
TEST_F(ScalarEvolutionsTest, SCEVCacheNUW) {
/*
* Create the following code:
* func(i64 %a)
* entry:
* %s1 = add i64 %a, -1
* %s2 = add nuw i64 %a, -1
* br label %exit
* exit:
* ret %s
*/
// Create a module.
Module M("SCEVCacheNUW", Context);
Type *T_int64 = Type::getInt64Ty(Context);
FunctionType *FTy =
FunctionType::get(Type::getVoidTy(Context), { T_int64 }, false);
Function *F = cast<Function>(M.getOrInsertFunction("func", FTy));
Argument *Arg = &*F->arg_begin();
ConstantInt *C = ConstantInt::get(Context, APInt(64, -1));
BasicBlock *Entry = BasicBlock::Create(Context, "entry", F);
BasicBlock *Exit = BasicBlock::Create(Context, "exit", F);
IRBuilder<> Builder(Entry);
auto *S1 = cast<Instruction>(Builder.CreateAdd(Arg, C, "add"));
auto *S2 = cast<Instruction>(Builder.CreateAdd(Arg, C, "add"));
S2->setHasNoUnsignedWrap(true);
Builder.CreateBr(Exit);
Builder.SetInsertPoint(Exit);
auto *R = cast<Instruction>(Builder.CreateRetVoid());
ScalarEvolution SE = buildSE(*F);
// Get S2 first to move it to cache.
const SCEV *SC2 = SE.getSCEV(S2);
EXPECT_TRUE(isa<SCEVAddExpr>(SC2));
// Now get S1.
const SCEV *SC1 = SE.getSCEV(S1);
EXPECT_TRUE(isa<SCEVAddExpr>(SC1));
// Expand for S1, it should use S1 not S2 in spite S2
// first in the cache.
SCEVExpander Exp(SE, M.getDataLayout(), "expander");
auto *I = cast<Instruction>(Exp.expandCodeFor(SC1, nullptr, R));
EXPECT_FALSE(I->hasNoUnsignedWrap());
}
// Check that SCEV does not save the SCEV -> V
// mapping of SCEV differ from V in NSW flag.
TEST_F(ScalarEvolutionsTest, SCEVCacheNSW) {
/*
* Create the following code:
* func(i64 %a)
* entry:
* %s1 = add i64 %a, -1
* %s2 = add nsw i64 %a, -1
* br label %exit
* exit:
* ret %s
*/
// Create a module.
Module M("SCEVCacheNUW", Context);
Type *T_int64 = Type::getInt64Ty(Context);
FunctionType *FTy =
FunctionType::get(Type::getVoidTy(Context), { T_int64 }, false);
Function *F = cast<Function>(M.getOrInsertFunction("func", FTy));
Argument *Arg = &*F->arg_begin();
ConstantInt *C = ConstantInt::get(Context, APInt(64, -1));
BasicBlock *Entry = BasicBlock::Create(Context, "entry", F);
BasicBlock *Exit = BasicBlock::Create(Context, "exit", F);
IRBuilder<> Builder(Entry);
auto *S1 = cast<Instruction>(Builder.CreateAdd(Arg, C, "add"));
auto *S2 = cast<Instruction>(Builder.CreateAdd(Arg, C, "add"));
S2->setHasNoSignedWrap(true);
Builder.CreateBr(Exit);
Builder.SetInsertPoint(Exit);
auto *R = cast<Instruction>(Builder.CreateRetVoid());
ScalarEvolution SE = buildSE(*F);
// Get S2 first to move it to cache.
const SCEV *SC2 = SE.getSCEV(S2);
EXPECT_TRUE(isa<SCEVAddExpr>(SC2));
// Now get S1.
const SCEV *SC1 = SE.getSCEV(S1);
EXPECT_TRUE(isa<SCEVAddExpr>(SC1));
// Expand for S1, it should use S1 not S2 in spite S2
// first in the cache.
SCEVExpander Exp(SE, M.getDataLayout(), "expander");
auto *I = cast<Instruction>(Exp.expandCodeFor(SC1, nullptr, R));
EXPECT_FALSE(I->hasNoSignedWrap());
}
} // end anonymous namespace
} // end namespace llvm