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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 

llvm-svn: 161451
This commit is contained in:
Evan Cheng 2012-08-07 22:21:00 +00:00
parent 45edb704d3
commit fbdd25c135
2 changed files with 52 additions and 6 deletions
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22
llvm/lib/Target/X86/X86ISelLowering.cpp
View File

@ -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.

36
llvm/test/CodeGen/X86/2012-08-07-CmpISelBug.ll Normal file
View File

@ -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
}