We can use the C flag from NEG to detect that the input was zero.
Really we could probably use the Z flag too. But C matches what
we'd do for usubo 0, X.
Haven't found a test case for this due to the usubo formation
in CGP. But I verified if I comment out the CGP code this
transformation catches some of the same cases.
llvm-svn: 365929
static X86::CondCode isUseDefConvertible(const MachineInstr &MI) {
switch (MI.getOpcode()) {
default: return X86::COND_INVALID;
+ case X86::NEG8r:
+ case X86::NEG16r:
+ case X86::NEG32r:
+ case X86::NEG64r:
+ return X86::COND_AE;
case X86::LZCNT16rr:
case X86::LZCNT32rr:
case X86::LZCNT64rr: