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Improve constant folding of undef for cmp and select operators.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@134223 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2011-07-01 01:03:43 +00:00
parent 5e653c925c
commit 68c0dbc14f
3 changed files with 39 additions and 6 deletions
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8
lib/Analysis/InstructionSimplify.cpp
View File

@ -2204,15 +2204,15 @@ Value *llvm::SimplifySelectInst(Value *CondVal, Value *TrueVal, Value *FalseVal,
if (TrueVal == FalseVal)
return TrueVal;
if (isa<UndefValue>(TrueVal)) // select C, undef, X -> X
return FalseVal;
if (isa<UndefValue>(FalseVal)) // select C, X, undef -> X
return TrueVal;
if (isa<UndefValue>(CondVal)) { // select undef, X, Y -> X or Y
if (isa<Constant>(TrueVal))
return TrueVal;
return FalseVal;
}
if (isa<UndefValue>(TrueVal)) // select C, undef, X -> X
return FalseVal;
if (isa<UndefValue>(FalseVal)) // select C, X, undef -> X
return TrueVal;
return 0;
}

9
lib/VMCore/ConstantFold.cpp
View File

@ -730,9 +730,12 @@ Constant *llvm::ConstantFoldSelectInstruction(Constant *Cond,
}
if (isa<UndefValue>(Cond)) {
if (isa<UndefValue>(V1)) return V1;
return V2;
}
if (isa<UndefValue>(V1)) return V2;
if (isa<UndefValue>(V2)) return V1;
if (isa<UndefValue>(Cond)) return V1;
if (V1 == V2) return V1;
if (ConstantExpr *TrueVal = dyn_cast<ConstantExpr>(V1)) {
@ -1851,7 +1854,9 @@ Constant *llvm::ConstantFoldCompareInstruction(unsigned short pred,
if (isa<UndefValue>(C1) || isa<UndefValue>(C2)) {
// For EQ and NE, we can always pick a value for the undef to make the
// predicate pass or fail, so we can return undef.
if (ICmpInst::isEquality(ICmpInst::Predicate(pred)))
// Also, if both operands are undef, we can return undef.
if (ICmpInst::isEquality(ICmpInst::Predicate(pred)) ||
(isa<UndefValue>(C1) && isa<UndefValue>(C2)))
return UndefValue::get(ResultTy);
// Otherwise, pick the same value as the non-undef operand, and fold
// it to true or false.

28
test/Transforms/InstSimplify/binop.ll → test/Transforms/InstSimplify/undef.ll
View File

@ -97,3 +97,31 @@ define i64 @test13() {
%r = lshr i64 undef, undef
ret i64 %r
}
; @test14
; CHECK: ret i1 undef
define i1 @test14() {
%r = icmp slt i64 undef, undef
ret i1 %r
}
; @test15
; CHECK: ret i1 undef
define i1 @test15() {
%r = icmp ult i64 undef, undef
ret i1 %r
}
; @test16
; CHECK: ret i64 undef
define i64 @test16(i64 %a) {
%r = select i1 undef, i64 %a, i64 undef
ret i64 %r
}
; @test17
; CHECK: ret i64 undef
define i64 @test17(i64 %a) {
%r = select i1 undef, i64 undef, i64 %a
ret i64 %r
}