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PR10267: Don't combine an equality compare with an AND into an inequality compare when the AND has more than one use.

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This can pessimize code, inequalities are generally more expensive.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@134379 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer
2011-07-04 20:16:36 +00:00
parent cbb11869c4
commit fc87cdc1f4
2 changed files with 17 additions and 1 deletions
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6
lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@@ -1454,7 +1454,11 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI,
return new ICmpInst(isICMP_NE ? ICmpInst::ICMP_EQ : return new ICmpInst(isICMP_NE ? ICmpInst::ICMP_EQ :
ICmpInst::ICMP_NE, LHSI, ICmpInst::ICMP_NE, LHSI,
Constant::getNullValue(RHS->getType())); Constant::getNullValue(RHS->getType()));
// Don't perform the following transforms if the AND has multiple uses
if (!BO->hasOneUse())
break;
// Replace (and X, (1 << size(X)-1) != 0) with x s< 0 // Replace (and X, (1 << size(X)-1) != 0) with x s< 0
if (BOC->getValue().isSignBit()) { if (BOC->getValue().isSignBit()) {
Value *X = BO->getOperand(0); Value *X = BO->getOperand(0);

12
test/Transforms/InstCombine/icmp.ll
View File

@@ -547,3 +547,15 @@ define i1 @test56(i32 %a) {
%cmp = icmp eq i32 %sub, 123 %cmp = icmp eq i32 %sub, 123
ret i1 %cmp ret i1 %cmp
} }
; PR10267 Don't make icmps more expensive when no other inst is subsumed.
declare void @foo(i32)
; CHECK: @test57
; CHECK: %and = and i32 %a, -2
; CHECK: %cmp = icmp ne i32 %and, 0
define i1 @test57(i32 %a) {
%and = and i32 %a, -2
%cmp = icmp ne i32 %and, 0
call void @foo(i32 %and)
ret i1 %cmp
}