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Fix a bogus optimization: folding (slt (zext i1 A to i32), 1) -> (slt i1 A, true)

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This cause a regression in InstCombine/JavaCompare, which was doing the right
thing on accident.  To handle the missed case, generalize the comparisons based
on masked bits a little bit to handle comparisons against the max value. For 
example, we can now xform (slt i32 (and X, 4), 4) -> (setne i32 (and X, 4), 4)

llvm-svn: 53443
This commit is contained in:
Chris Lattner 2008-07-11 04:09:09 +00:00
parent 43a2b1b16d
commit f3f6b6d7af
2 changed files with 23 additions and 16 deletions
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31
lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -5230,7 +5230,7 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
// See if we are doing a comparison between a constant and an instruction that
// can be folded into the comparison.
if (ConstantInt *CI = dyn_cast<ConstantInt>(Op1)) {
Value *A, *B;
Value *A, *B;
// (icmp ne/eq (sub A B) 0) -> (icmp ne/eq A, B)
if (I.isEquality() && CI->isNullValue() &&
@ -5396,6 +5396,8 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
return ReplaceInstUsesWith(I, ConstantInt::getTrue());
if (Min.sgt(RHSVal))
return ReplaceInstUsesWith(I, ConstantInt::getFalse());
if (Max == RHSVal) // A <s MAX -> A != MAX
return new ICmpInst(ICmpInst::ICMP_NE, Op0, Op1);
break;
case ICmpInst::ICMP_SGT:
if (Min.sgt(RHSVal))
@ -6300,12 +6302,11 @@ Instruction *InstCombiner::visitICmpInstWithCastAndCast(ICmpInst &ICI) {
// %B = icmp ugt short %X, 1330
// because %A may have negative value.
//
// However, it is OK if SrcTy is bool (See cast-set.ll testcase)
// OR operation is EQ/NE.
if (isSignedExt == isSignedCmp || SrcTy == Type::Int1Ty || ICI.isEquality())
// However, we allow this when the compare is EQ/NE, because they are
// signless.
if (isSignedExt == isSignedCmp || ICI.isEquality())
return new ICmpInst(ICI.getPredicate(), LHSCIOp, Res1);
else
return 0;
return 0;
}
// The re-extended constant changed so the constant cannot be represented
@ -6343,17 +6344,15 @@ Instruction *InstCombiner::visitICmpInstWithCastAndCast(ICmpInst &ICI) {
// Finally, return the value computed.
if (ICI.getPredicate() == ICmpInst::ICMP_ULT ||
ICI.getPredicate() == ICmpInst::ICMP_SLT) {
ICI.getPredicate() == ICmpInst::ICMP_SLT)
return ReplaceInstUsesWith(ICI, Result);
} else {
assert((ICI.getPredicate()==ICmpInst::ICMP_UGT ||
ICI.getPredicate()==ICmpInst::ICMP_SGT) &&
"ICmp should be folded!");
if (Constant *CI = dyn_cast<Constant>(Result))
return ReplaceInstUsesWith(ICI, ConstantExpr::getNot(CI));
else
return BinaryOperator::CreateNot(Result);
}
assert((ICI.getPredicate()==ICmpInst::ICMP_UGT ||
ICI.getPredicate()==ICmpInst::ICMP_SGT) &&
"ICmp should be folded!");
if (Constant *CI = dyn_cast<Constant>(Result))
return ReplaceInstUsesWith(ICI, ConstantExpr::getNot(CI));
return BinaryOperator::CreateNot(Result);
}
Instruction *InstCombiner::visitShl(BinaryOperator &I) {

8
test/Transforms/InstCombine/2008-07-10-CastSextBool.ll Normal file
View File

@ -0,0 +1,8 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep {%C = xor i1 %A, true}
; PR2539
define i1 @test(i1 %A) {
%B = zext i1 %A to i32
%C = icmp slt i32 %B, 1
ret i1 %C
}