[FastISel][X86] Support FNeg instruction in target independent fast isel handling

[craig.topper]

Summary

This patch adds support for calling selectFNeg for FNeg instructions in addition to the fsub idiom

[cameron.mcinally]

LGTM

[cameron.mcinally]

If we end up with more UnaryOps in the future, it would make sense to create a selectUnaryOp(...). But that's probably overkill for now since no new UnOps are planned.

llvm/lib/CodeGen/SelectionDAG/FastISel.cpp

case Instruction::AShr:
     return selectBinaryOp(I, ISD::SRA);
   case Instruction::And:
     return selectBinaryOp(I, ISD::AND);
   case Instruction::Or:
     return selectBinaryOp(I, ISD::OR);
   case Instruction::Xor:
     return selectBinaryOp(I, ISD::XOR);
 
+  case Instruction::FNeg:
+    return selectFNeg(I, I->getOperand(0));
+
   case Instruction::GetElementPtr:
     return selectGetElementPtr(I);
 
   case Instruction::Br: {
     const BranchInst *BI = cast<BranchInst>(I);
 
     if (BI->isUnconditional()) {
       const BasicBlock *LLVMSucc = BI->getSuccessor(0);

llvm/test/CodeGen/X86/fast-isel-fneg.ll

 ; SSE2-NEXT:    movd %ecx, %xmm0
 ; SSE2-NEXT:    movd %xmm0, (%eax)
 ; SSE2-NEXT:    retl
   %a = load float, float* %x
   %b = fsub float -0.0, %a
   store float %b, float* %y
   ret void
 }
+
+define double @too(double %x) nounwind {
+; CHECK-LABEL: too:
+; CHECK:       ## %bb.0:
+; CHECK-NEXT:    movq %xmm0, %rax
+; CHECK-NEXT:    movabsq $-9223372036854775808, %rcx ## imm = 0x8000000000000000
+; CHECK-NEXT:    xorq %rax, %rcx
+; CHECK-NEXT:    movq %rcx, %xmm0
+; CHECK-NEXT:    retq
+;
+; SSE2-LABEL: too:
+; SSE2:       # %bb.0:
+; SSE2-NEXT:    pushl %ebp
+; SSE2-NEXT:    movl %esp, %ebp
+; SSE2-NEXT:    andl $-8, %esp
+; SSE2-NEXT:    subl $8, %esp
+; SSE2-NEXT:    movsd {{.*#+}} xmm0 = mem[0],zero
+; SSE2-NEXT:    xorps {{\.LCPI.*}}, %xmm0
+; SSE2-NEXT:    movlps %xmm0, (%esp)
+; SSE2-NEXT:    fldl (%esp)
+; SSE2-NEXT:    movl %ebp, %esp
+; SSE2-NEXT:    popl %ebp
+; SSE2-NEXT:    retl
+  %y = fneg double %x
+  ret double %y
+}
+
+define float @zoo(float %x) nounwind {
+; CHECK-LABEL: zoo:
+; CHECK:       ## %bb.0:
+; CHECK-NEXT:    movd %xmm0, %eax
+; CHECK-NEXT:    xorl $2147483648, %eax ## imm = 0x80000000
+; CHECK-NEXT:    movd %eax, %xmm0
+; CHECK-NEXT:    retq
+;
+; SSE2-LABEL: zoo:
+; SSE2:       # %bb.0:
+; SSE2-NEXT:    pushl %eax
+; SSE2-NEXT:    movss {{.*#+}} xmm0 = mem[0],zero,zero,zero
+; SSE2-NEXT:    xorps {{\.LCPI.*}}, %xmm0
+; SSE2-NEXT:    movss %xmm0, (%esp)
+; SSE2-NEXT:    flds (%esp)
+; SSE2-NEXT:    popl %eax
+; SSE2-NEXT:    retl
+  %y = fneg float %x
+  ret float %y
+}