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[IRCE] isKnownNonNegative helper function 

Created a helper function to query for non negative SCEVs. Uses the
SGE predicate to catch constants that could be interpreted as
negative.

Differential Revision: https://reviews.llvm.org/D45481

llvm-svn: 329907
This commit is contained in:
Sam Parker 2018-04-12 12:49:40 +00:00
parent 294556d40e
commit 9737535943
2 changed files with 10 additions and 3 deletions
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11
llvm/lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
View File

@ -804,6 +804,13 @@ static bool CannotBeMinInLoop(const SCEV *BoundSCEV, Loop *L,
SE.getConstant(Min));
}
static bool isKnownNonNegativeInLoop(const SCEV *BoundSCEV, Loop *L,
ScalarEvolution &SE) {
const SCEV *Zero = SE.getZero(BoundSCEV->getType());
return SE.isAvailableAtLoopEntry(BoundSCEV, L) &&
SE.isLoopEntryGuardedByCond(L, ICmpInst::ICMP_SGE, BoundSCEV, Zero);
}
Optional<LoopStructure>
LoopStructure::parseLoopStructure(ScalarEvolution &SE,
BranchProbabilityInfo *BPI, Loop &L,
@ -963,8 +970,8 @@ LoopStructure::parseLoopStructure(ScalarEvolution &SE,
// If both parts are known non-negative, it is profitable to use
// unsigned comparison in increasing loop. This allows us to make the
// comparison check against "RightSCEV + 1" more optimistic.
if (SE.isKnownNonNegative(IndVarStart) &&
SE.isKnownNonNegative(RightSCEV))
if (isKnownNonNegativeInLoop(IndVarStart, &L, SE) &&
isKnownNonNegativeInLoop(RightSCEV, &L, SE))
Pred = ICmpInst::ICMP_ULT;
else
Pred = ICmpInst::ICMP_SLT;

2
llvm/test/Transforms/IRCE/variable-loop-bounds.ll
View File

@ -55,7 +55,7 @@ for.inc:
; CHECK-LABEL: test_inc_ne
; CHECK: main.exit.selector:
; CHECK: [[PSEUDO_PHI:%[^ ]+]] = phi i32 [ %inc, %for.inc ]
; CHECK: [[COND:%[^ ]+]] = icmp slt i32 [[PSEUDO_PHI]], %N
; CHECK: [[COND:%[^ ]+]] = icmp ult i32 [[PSEUDO_PHI]], %N
; CHECK: br i1 [[COND]], label %main.pseudo.exit, label %for.cond.cleanup.loopexit
define void @test_inc_ne(i32* nocapture %a, i32* nocapture readonly %b, i32* nocapture readonly %c, i32 %N) {
entry: