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Optimize icmp of null and select of two constants even if the select has

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multiple uses.  (The construct in question was found in gcc.)

llvm-svn: 91675
This commit is contained in:
Eli Friedman 2009-12-18 08:22:35 +00:00
parent d97d025eba
commit c8ab298dbd
2 changed files with 33 additions and 15 deletions
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32
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -6356,24 +6356,26 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
// comparison into the select arms, which will cause one to be
// constant folded and the select turned into a bitwise or.
Value *Op1 = 0, *Op2 = 0;
if (LHSI->hasOneUse()) {
if (Constant *C = dyn_cast<Constant>(LHSI->getOperand(1))) {
// Fold the known value into the constant operand.
Op1 = ConstantExpr::getICmp(I.getPredicate(), C, RHSC);
// Insert a new ICmp of the other select operand.
Op2 = Builder->CreateICmp(I.getPredicate(), LHSI->getOperand(2),
RHSC, I.getName());
} else if (Constant *C = dyn_cast<Constant>(LHSI->getOperand(2))) {
// Fold the known value into the constant operand.
Op2 = ConstantExpr::getICmp(I.getPredicate(), C, RHSC);
// Insert a new ICmp of the other select operand.
if (Constant *C = dyn_cast<Constant>(LHSI->getOperand(1)))
Op1 = ConstantExpr::getICmp(I.getPredicate(), C, RHSC);
if (Constant *C = dyn_cast<Constant>(LHSI->getOperand(2)))
Op2 = ConstantExpr::getICmp(I.getPredicate(), C, RHSC);
// We only want to perform this transformation if it will not lead to
// additional code. This is true if either both sides of the select
// fold to a constant (in which case the icmp is replaced with a select
// which will usually simplify) or this is the only user of the
// select (in which case we are trading a select+icmp for a simpler
// select+icmp).
if ((Op1 && Op2) || (LHSI->hasOneUse() && (Op1 || Op2))) {
if (!Op1)
Op1 = Builder->CreateICmp(I.getPredicate(), LHSI->getOperand(1),
RHSC, I.getName());
}
}
if (Op1)
if (!Op2)
Op2 = Builder->CreateICmp(I.getPredicate(), LHSI->getOperand(2),
RHSC, I.getName());
return SelectInst::Create(LHSI->getOperand(0), Op1, Op2);
}
break;
}
case Instruction::Call:

16
test/Transforms/InstCombine/2009-12-17-CmpSelectNull.ll Normal file
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@ -0,0 +1,16 @@
; RUN: opt < %s -instcombine -S | FileCheck %s
@.str254 = internal constant [2 x i8] c".\00"
@.str557 = internal constant [3 x i8] c"::\00"
define i8* @demangle_qualified(i32 %isfuncname) nounwind {
entry:
%tobool272 = icmp ne i32 %isfuncname, 0
%cond276 = select i1 %tobool272, i8* getelementptr inbounds ([2 x i8]* @.str254, i32 0, i32 0), i8* getelementptr inbounds ([3 x i8]* @.str557, i32 0, i32 0) ; <i8*> [#uses=4]
%cmp.i504 = icmp eq i8* %cond276, null
%rval = getelementptr i8* %cond276, i1 %cmp.i504
ret i8* %rval
}
; CHECK: %cond276 = select i1
; CHECK: ret i8* %cond276