From f299184565f5f0ff9e3bbb94dad184fd5a690c2c Mon Sep 17 00:00:00 2001 From: Chris Lattner Date: Fri, 11 Jul 2008 04:09:09 +0000 Subject: [PATCH] Fix a bogus optimization: folding (slt (zext i1 A to i32), 1) -> (slt i1 A, true) 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) git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@53443 91177308-0d34-0410-b5e6-96231b3b80d8 --- .../Scalar/InstructionCombining.cpp | 31 +++++++++---------- .../InstCombine/2008-07-10-CastSextBool.ll | 8 +++++ 2 files changed, 23 insertions(+), 16 deletions(-) create mode 100644 test/Transforms/InstCombine/2008-07-10-CastSextBool.ll diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp index e0e3f49be18..8cc7c05425b 100644 --- a/lib/Transforms/Scalar/InstructionCombining.cpp +++ b/lib/Transforms/Scalar/InstructionCombining.cpp @@ -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(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 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(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(Result)) + return ReplaceInstUsesWith(ICI, ConstantExpr::getNot(CI)); + return BinaryOperator::CreateNot(Result); } Instruction *InstCombiner::visitShl(BinaryOperator &I) { diff --git a/test/Transforms/InstCombine/2008-07-10-CastSextBool.ll b/test/Transforms/InstCombine/2008-07-10-CastSextBool.ll new file mode 100644 index 00000000000..f5efefb0a0b --- /dev/null +++ b/test/Transforms/InstCombine/2008-07-10-CastSextBool.ll @@ -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 +}