LLVM currently represents floating-point negation as -0.0 - x. Fix
FastISel to recognize this pattern and emit a floating-point
negation using xor.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@80963 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/llvm/CodeGen/FastISel.h b/include/llvm/CodeGen/FastISel.h
index b2cc94d..6cd5519 100644
--- a/include/llvm/CodeGen/FastISel.h
+++ b/include/llvm/CodeGen/FastISel.h
@@ -300,6 +300,8 @@
private:
bool SelectBinaryOp(User *I, ISD::NodeType ISDOpcode);
+ bool SelectFNeg(User *I);
+
bool SelectGetElementPtr(User *I);
bool SelectCall(User *I);
diff --git a/lib/CodeGen/SelectionDAG/FastISel.cpp b/lib/CodeGen/SelectionDAG/FastISel.cpp
index 5b4c79a..f0c7086 100644
--- a/lib/CodeGen/SelectionDAG/FastISel.cpp
+++ b/lib/CodeGen/SelectionDAG/FastISel.cpp
@@ -608,6 +608,26 @@
MBB->addSuccessor(MSucc);
}
+/// SelectFNeg - Emit an FNeg operation.
+///
+bool
+FastISel::SelectFNeg(User *I) {
+ unsigned OpReg = getRegForValue(BinaryOperator::getFNegArgument(I));
+ if (OpReg == 0) return false;
+
+ // Twiddle the sign bit with xor.
+ 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());
+ if (ResultReg == 0)
+ return false;
+
+ UpdateValueMap(I, ResultReg);
+ return true;
+}
+
bool
FastISel::SelectOperator(User *I, unsigned Opcode) {
switch (Opcode) {
@@ -618,6 +638,9 @@
case Instruction::Sub:
return SelectBinaryOp(I, ISD::SUB);
case Instruction::FSub:
+ // FNeg is currently represented in LLVM IR as a special case of FSub.
+ if (BinaryOperator::isFNeg(I))
+ return SelectFNeg(I);
return SelectBinaryOp(I, ISD::FSUB);
case Instruction::Mul:
return SelectBinaryOp(I, ISD::MUL);
diff --git a/test/CodeGen/X86/fast-isel-fneg.ll b/test/CodeGen/X86/fast-isel-fneg.ll
new file mode 100644
index 0000000..41b288b
--- /dev/null
+++ b/test/CodeGen/X86/fast-isel-fneg.ll
@@ -0,0 +1,15 @@
+; RUN: llvm-as < %s | llc -fast-isel -march=x86-64 | FileCheck %s
+
+; CHECK: doo:
+; CHECK: xorpd
+define double @doo(double %x) nounwind {
+ %y = fsub double -0.0, %x
+ ret double %y
+}
+
+; CHECK: foo:
+; CHECK: xorps
+define float @foo(float %x) nounwind {
+ %y = fsub float -0.0, %x
+ ret float %y
+}