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InstCombine: creating selects from -1 and 0 is fine, they combine into a sext from i1.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122453 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer 2010-12-22 23:12:15 +00:00
parent e915ff30cd
commit 4ac19470dc
2 changed files with 18 additions and 3 deletions
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9
lib/Transforms/InstCombine/InstCombineSelect.cpp
View File

@ -195,7 +195,10 @@ static bool isSelect01(Constant *C1, Constant *C2) {
ConstantInt *C2I = dyn_cast<ConstantInt>(C2); ConstantInt *C2I = dyn_cast<ConstantInt>(C2);
if (!C2I) if (!C2I)
return false; return false;
return (C1I->isZero() || C1I->isOne()) && (C2I->isZero() || C2I->isOne()); if (!C1I->isZero() && !C2I->isZero()) // One side must be zero.
return false;
return C1I->isOne() || C1I->isAllOnesValue() ||
C2I->isOne() || C2I->isAllOnesValue();
} }
/// FoldSelectIntoOp - Try fold the select into one of the operands to /// FoldSelectIntoOp - Try fold the select into one of the operands to
@ -219,7 +222,7 @@ Instruction *InstCombiner::FoldSelectIntoOp(SelectInst &SI, Value *TrueVal,
Constant *C = GetSelectFoldableConstant(TVI); Constant *C = GetSelectFoldableConstant(TVI);
Value *OOp = TVI->getOperand(2-OpToFold); Value *OOp = TVI->getOperand(2-OpToFold);
// Avoid creating select between 2 constants unless it's selecting // Avoid creating select between 2 constants unless it's selecting
// between 0 and 1. // between 0, 1 and -1.
if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) { if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) {
Instruction *NewSel = SelectInst::Create(SI.getCondition(), OOp, C); Instruction *NewSel = SelectInst::Create(SI.getCondition(), OOp, C);
InsertNewInstBefore(NewSel, SI); InsertNewInstBefore(NewSel, SI);
@ -248,7 +251,7 @@ Instruction *InstCombiner::FoldSelectIntoOp(SelectInst &SI, Value *TrueVal,
Constant *C = GetSelectFoldableConstant(FVI); Constant *C = GetSelectFoldableConstant(FVI);
Value *OOp = FVI->getOperand(2-OpToFold); Value *OOp = FVI->getOperand(2-OpToFold);
// Avoid creating select between 2 constants unless it's selecting // Avoid creating select between 2 constants unless it's selecting
// between 0 and 1. // between 0, 1 and -1.
if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) { if (!isa<Constant>(OOp) || isSelect01(C, cast<Constant>(OOp))) {
Instruction *NewSel = SelectInst::Create(SI.getCondition(), C, OOp); Instruction *NewSel = SelectInst::Create(SI.getCondition(), C, OOp);
InsertNewInstBefore(NewSel, SI); InsertNewInstBefore(NewSel, SI);

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

@ -584,3 +584,15 @@ define i32 @test41(i1 %cond, i32 %x, i32 %y) {
; CHECK-NEXT: and i32 %x, %y ; CHECK-NEXT: and i32 %x, %y
; CHECK-NEXT: ret i32 ; CHECK-NEXT: ret i32
} }
define i32 @test42(i32 %x, i32 %y) {
%b = add i32 %y, -1
%cond = icmp eq i32 %x, 0
%c = select i1 %cond, i32 %b, i32 %y
ret i32 %c
; CHECK: @test42
; CHECK-NEXT: %cond = icmp eq i32 %x, 0
; CHECK-NEXT: %b = sext i1 %cond to i32
; CHECK-NEXT: %c = add i32 %b, %y
; CHECK-NEXT: ret i32 %c
}