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Scev assume finite flag #91104

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Scev assume finite flag #91104

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c565851
adding AssumeLoopExists flag
skewballfox May 5, 2024
0dfb651
add AssumeLoopExists test
ZuseZ4 May 5, 2024
f10bf09
cleanup
ZuseZ4 May 5, 2024
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3 changes: 3 additions & 0 deletions llvm/include/llvm/Analysis/ScalarEvolution.h
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Original file line number Diff line number Diff line change
Expand Up @@ -460,6 +460,9 @@ class ScalarEvolution {
LoopComputable ///< The SCEV varies predictably with the loop.
};

bool AssumeLoopFinite = false;
void setAssumeLoopExits();

/// An enum describing the relationship between a SCEV and a basic block.
enum BlockDisposition {
DoesNotDominateBlock, ///< The SCEV does not dominate the block.
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5 changes: 4 additions & 1 deletion llvm/lib/Analysis/ScalarEvolution.cpp
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Expand Up @@ -509,6 +509,8 @@ const SCEV *ScalarEvolution::getVScale(Type *Ty) {
return S;
}

void ScalarEvolution::setAssumeLoopExits() { this->AssumeLoopFinite = true; }

const SCEV *ScalarEvolution::getElementCount(Type *Ty, ElementCount EC) {
const SCEV *Res = getConstant(Ty, EC.getKnownMinValue());
if (EC.isScalable())
Expand Down Expand Up @@ -7422,7 +7424,8 @@ bool ScalarEvolution::loopIsFiniteByAssumption(const Loop *L) {
// A mustprogress loop without side effects must be finite.
// TODO: The check used here is very conservative. It's only *specific*
// side effects which are well defined in infinite loops.
return isFinite(L) || (isMustProgress(L) && loopHasNoSideEffects(L));
return AssumeLoopFinite || isFinite(L) ||
(isMustProgress(L) && loopHasNoSideEffects(L));
}

const SCEV *ScalarEvolution::createSCEVIter(Value *V) {
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29 changes: 29 additions & 0 deletions llvm/unittests/Analysis/ScalarEvolutionTest.cpp
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Expand Up @@ -1085,6 +1085,35 @@ TEST_F(ScalarEvolutionsTest, SCEVComputeExpressionSize) {
EXPECT_EQ(S2S->getExpressionSize(), 5u);
}

TEST_F(ScalarEvolutionsTest, AssumeLoopExists) {
LLVMContext C;
SMDiagnostic Err;
std::unique_ptr<Module> M = parseAssemblyString(
"define void @foo(i32 %N) { "
"entry: "
" %cmp3 = icmp sgt i32 %N, 0 "
" br i1 %cmp3, label %for.body, label %for.cond.cleanup "
"for.cond.cleanup: "
" ret void "
"for.body: "
" br label %for.body "
"} "
Err, C);

ASSERT_TRUE(M && "Could not parse module?");
ASSERT_TRUE(!verifyModule(*M) && "Must have been well formed!");

runWithSE(*M, "foo", [&](Function &F, LoopInfo &LI, ScalarEvolution &SE) {
BasicBlock *L = F.begin()->getNextNode()->getNextNode();
auto *Loop = LI.getLoopFor(L);
bool IsFinite = SE.loopIsFiniteByAssumption(Loop);
EXPECT_FALSE(IsFinite);
SE.setAssumeLoopExits();
IsFinite = SE.loopIsFiniteByAssumption(Loop);
EXPECT_TRUE(IsFinite);
});
}

TEST_F(ScalarEvolutionsTest, SCEVLoopDecIntrinsic) {
LLVMContext C;
SMDiagnostic Err;
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