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Canonicalize boolean +/- a constant to a select.

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(I think it's reasonably clear that we want to have a canonical form for 
constructs like this; if anyone thinks that a select is not the best 
canonical form, please tell me.)



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@75531 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Eli Friedman 2009-07-13 22:27:52 +00:00
parent ddf9f99a9f
commit 709b33dc78
2 changed files with 39 additions and 6 deletions
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14
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -2101,13 +2101,10 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
if (SimplifyDemandedInstructionBits(I)) if (SimplifyDemandedInstructionBits(I))
return &I; return &I;
// zext(i1) - 1 -> select i1, 0, -1 // zext(bool) + C -> bool ? C + 1 : C
if (ZExtInst *ZI = dyn_cast<ZExtInst>(LHS)) if (ZExtInst *ZI = dyn_cast<ZExtInst>(LHS))
if (CI->isAllOnesValue() && if (ZI->getSrcTy() == Type::Int1Ty)
ZI->getOperand(0)->getType() == Type::Int1Ty) return SelectInst::Create(ZI->getOperand(0), AddOne(CI, Context), CI);
return SelectInst::Create(ZI->getOperand(0),
Context->getNullValue(I.getType()),
Context->getAllOnesValue(I.getType()));
} }
if (isa<PHINode>(LHS)) if (isa<PHINode>(LHS))
@ -2525,6 +2522,11 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
if (SelectInst *SI = dyn_cast<SelectInst>(Op1)) if (SelectInst *SI = dyn_cast<SelectInst>(Op1))
if (Instruction *R = FoldOpIntoSelect(I, SI, this)) if (Instruction *R = FoldOpIntoSelect(I, SI, this))
return R; return R;
// C - zext(bool) -> bool ? C - 1 : C
if (ZExtInst *ZI = dyn_cast<ZExtInst>(Op1))
if (ZI->getSrcTy() == Type::Int1Ty)
return SelectInst::Create(ZI->getOperand(0), SubOne(C, Context), C);
} }
if (I.getType() == Type::Int1Ty) if (I.getType() == Type::Int1Ty)

31
test/Transforms/InstCombine/zext-bool-add-sub.ll Normal file
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@ -0,0 +1,31 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep {zext } | count 0
define i32 @a(i1 %x) {
entry:
%y = zext i1 %x to i32
%res = add i32 %y, 1
ret i32 %res
}
define i32 @b(i1 %x) {
entry:
%y = zext i1 %x to i32
%res = add i32 %y, -1
ret i32 %res
}
define i32 @c(i1 %x) {
entry:
%y = zext i1 %x to i32
%res = sub i32 0, %y
ret i32 %res
}
define i32 @d(i1 %x) {
entry:
%y = zext i1 %x to i32
%res = sub i32 3, %y
ret i32 %res
}