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Fix a thinko: When lowering fneg with xor, bitcast the operands

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from floating-point to integer first, and bitcast the result
back to floating-point. Previously, this test was passing by
falling back to SelectionDAG lowering. The resulting code isn't
as nice, but it's correct and CodeGen now stays on the fast path.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@81171 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2009-09-07 23:47:14 +00:00
parent 6e9057b0ef
commit fd06aa7c07
2 changed files with 20 additions and 7 deletions
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21
lib/CodeGen/SelectionDAG/FastISel.cpp
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@ -615,12 +615,25 @@ FastISel::SelectFNeg(User *I) {
unsigned OpReg = getRegForValue(BinaryOperator::getFNegArgument(I));
if (OpReg == 0) return false;
// Twiddle the sign bit with xor.
// Bitcast the value to integer, twiddle the sign bit with xor,
// and then bitcast it back to floating-point.
EVT VT = TLI.getValueType(I->getType());
if (VT.getSizeInBits() > 64) return false;
unsigned ResultReg = FastEmit_ri_(VT.getSimpleVT(), ISD::XOR, OpReg,
UINT64_C(1) << (VT.getSizeInBits()-1),
VT.getSimpleVT());
EVT IntVT = EVT::getIntegerVT(I->getContext(), VT.getSizeInBits());
unsigned IntReg = FastEmit_r(VT.getSimpleVT(), IntVT.getSimpleVT(),
ISD::BIT_CONVERT, OpReg);
if (IntReg == 0)
return false;
unsigned IntResultReg = FastEmit_ri_(IntVT.getSimpleVT(), ISD::XOR, IntReg,
UINT64_C(1) << (VT.getSizeInBits()-1),
IntVT.getSimpleVT());
if (IntResultReg == 0)
return false;
unsigned ResultReg = FastEmit_r(IntVT.getSimpleVT(), VT.getSimpleVT(),
ISD::BIT_CONVERT, IntResultReg);
if (ResultReg == 0)
return false;

6
test/CodeGen/X86/fast-isel-fneg.ll
View File

@ -1,14 +1,14 @@
; RUN: llvm-as < %s | llc -fast-isel -march=x86-64 | FileCheck %s
; RUN: llvm-as < %s | llc -fast-isel -fast-isel-abort -march=x86-64 | FileCheck %s
; CHECK: doo:
; CHECK: xorpd
; CHECK: xor
define double @doo(double %x) nounwind {
%y = fsub double -0.0, %x
ret double %y
}
; CHECK: foo:
; CHECK: xorps
; CHECK: xor
define float @foo(float %x) nounwind {
%y = fsub float -0.0, %x
ret float %y