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[EarlyCSE] Fix hashing of self-compares 

Summary:
Update compare normalization in SimpleValue hashing to break ties (when
the same value is being compared to itself) by switching to the swapped
predicate if it has a lower numerical value.  This brings the hashing in
line with isEqual, which already recognizes the self-compares with
swapped predicates as equal.

Fixes PR 42280.

Reviewers: spatel, efriedma, nikic, fhahn, uabelho

Reviewed By: nikic

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D63349

llvm-svn: 363598
This commit is contained in:
Joseph Tremoulet 2019-06-17 19:11:28 +00:00
parent 7a0098aa6e
commit daa1ae6142
2 changed files with 23 additions and 2 deletions
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9
llvm/lib/Transforms/Scalar/EarlyCSE.cpp
View File

@ -174,12 +174,17 @@ static unsigned getHashValueImpl(SimpleValue Val) {
}
if (CmpInst *CI = dyn_cast<CmpInst>(Inst)) {
// Compares can be commuted by swapping the comparands and
// updating the predicate. Choose the form that has the
// comparands in sorted order, or in the case of a tie, the
// one with the lower predicate.
Value *LHS = CI->getOperand(0);
Value *RHS = CI->getOperand(1);
CmpInst::Predicate Pred = CI->getPredicate();
if (Inst->getOperand(0) > Inst->getOperand(1)) {
CmpInst::Predicate SwappedPred = CI->getSwappedPredicate();
if (std::tie(LHS, Pred) > std::tie(RHS, SwappedPred)) {
std::swap(LHS, RHS);
Pred = CI->getSwappedPredicate();
Pred = SwappedPred;
}
return hash_combine(Inst->getOpcode(), Pred, LHS, RHS);
}

16
llvm/test/Transforms/EarlyCSE/commute.ll
View File

@ -72,6 +72,22 @@ define void @test5(i32 %A, i32 %B, i1* %PA, i1* %PB) {
ret void
}
; Test degenerate case of commuted compare of identical comparands.
define void @test6(float %f, i1* %p1, i1* %p2) {
; CHECK-LABEL: @test6(
; CHECK-NEXT: [[C1:%.*]] = fcmp ult float [[F:%.*]], [[F]]
; CHECK-NEXT: store i1 [[C1]], i1* [[P1:%.*]]
; CHECK-NEXT: store i1 [[C1]], i1* [[P2:%.*]]
; CHECK-NEXT: ret void
;
%c1 = fcmp ult float %f, %f
%c2 = fcmp ugt float %f, %f
store i1 %c1, i1* %p1
store i1 %c2, i1* %p2
ret void
}
; Min/max operands may be commuted in the compare and select.
define i8 @smin_commute(i8 %a, i8 %b) {