From b64dd5f2b5a9989a8b1006d0aa82428455da039a Mon Sep 17 00:00:00 2001 From: Evan Cheng Date: Tue, 7 Aug 2012 22:21:00 +0000 Subject: [PATCH] X86 cmp lowering is looking past truncate on the condition node. It should only do so when the high bits are known zero. This caused a subtle miscompilation. rdar://12027825 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@161451 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Target/X86/X86ISelLowering.cpp | 22 ++++++++++---- test/CodeGen/X86/2012-08-07-CmpISelBug.ll | 36 +++++++++++++++++++++++ 2 files changed, 52 insertions(+), 6 deletions(-) create mode 100644 test/CodeGen/X86/2012-08-07-CmpISelBug.ll diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp index 8125b4c1ad6..d70cdb8a762 100644 --- a/lib/Target/X86/X86ISelLowering.cpp +++ b/lib/Target/X86/X86ISelLowering.cpp @@ -8741,6 +8741,16 @@ static bool isAllOnes(SDValue V) { return C && C->isAllOnesValue(); } +static bool isTruncWithZeroHighBitsInput(SDValue V, SelectionDAG &DAG) { + if (V.getOpcode() != ISD::TRUNCATE) + return false; + + SDValue VOp0 = V.getOperand(0); + unsigned InBits = VOp0.getValueSizeInBits(); + unsigned Bits = V.getValueSizeInBits(); + return DAG.MaskedValueIsZero(VOp0, APInt::getHighBitsSet(InBits,InBits-Bits)); +} + SDValue X86TargetLowering::LowerSELECT(SDValue Op, SelectionDAG &DAG) const { bool addTest = true; SDValue Cond = Op.getOperand(0); @@ -8910,9 +8920,9 @@ SDValue X86TargetLowering::LowerSELECT(SDValue Op, SelectionDAG &DAG) const { } if (addTest) { - // Look pass the truncate. - if (Cond.getOpcode() == ISD::TRUNCATE) - Cond = Cond.getOperand(0); + // Look pass the truncate if the high bits are known zero. + if (isTruncWithZeroHighBitsInput(Cond, DAG)) + Cond = Cond.getOperand(0); // We know the result of AND is compared against zero. Try to match // it to BT. @@ -9219,9 +9229,9 @@ SDValue X86TargetLowering::LowerBRCOND(SDValue Op, SelectionDAG &DAG) const { } if (addTest) { - // Look pass the truncate. - if (Cond.getOpcode() == ISD::TRUNCATE) - Cond = Cond.getOperand(0); + // Look pass the truncate if the high bits are known zero. + if (isTruncWithZeroHighBitsInput(Cond, DAG)) + Cond = Cond.getOperand(0); // We know the result of AND is compared against zero. Try to match // it to BT. diff --git a/test/CodeGen/X86/2012-08-07-CmpISelBug.ll b/test/CodeGen/X86/2012-08-07-CmpISelBug.ll new file mode 100644 index 00000000000..000b853ab8f --- /dev/null +++ b/test/CodeGen/X86/2012-08-07-CmpISelBug.ll @@ -0,0 +1,36 @@ +; RUN: llc < %s -mtriple=x86_64-apple-macosx | FileCheck %s + +; Cmp lowering should not look past the truncate unless the high bits are known +; zero. +; rdar://12027825 + +define void @foo(i8 %arg4, i32 %arg5, i32* %arg14) nounwind { +bb: +; CHECK: foo: +; CHECK-NOT: testl +; CHECK: testb + %tmp48 = zext i8 %arg4 to i32 + %tmp49 = and i32 %tmp48, 32 + %tmp50 = add i32 %tmp49, 1593371643 + %tmp55 = sub i32 %tmp50, 0 + %tmp56 = add i32 %tmp55, 7787538 + %tmp57 = xor i32 %tmp56, 1601159181 + %tmp58 = xor i32 %arg5, 1601159181 + %tmp59 = and i32 %tmp57, %tmp58 + %tmp60 = add i32 %tmp59, -1263900958 + %tmp67 = sub i32 %tmp60, 0 + %tmp103 = xor i32 %tmp56, 13 + %tmp104 = trunc i32 %tmp103 to i8 + %tmp105 = sub i8 0, %tmp104 + %tmp106 = add i8 %tmp105, -103 + %tmp113 = sub i8 %tmp106, 0 + %tmp114 = add i8 %tmp113, -72 + %tmp141 = icmp ne i32 %tmp67, -1263900958 + %tmp142 = select i1 %tmp141, i8 %tmp114, i8 undef + %tmp143 = xor i8 %tmp142, 81 + %tmp144 = zext i8 %tmp143 to i32 + %tmp145 = add i32 %tmp144, 2062143348 + %tmp152 = sub i32 %tmp145, 0 + store i32 %tmp152, i32* %arg14 + ret void +} -- 2.34.1