[X86] Add NEG to isUseDefConvertible.

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

diff --git a/llvm/lib/Target/X86/X86InstrInfo.cpp b/llvm/lib/Target/X86/X86InstrInfo.cpp
index 1df41b9..62ed00b 100644 (file)
--- a/llvm/lib/Target/X86/X86InstrInfo.cpp
+++ b/llvm/lib/Target/X86/X86InstrInfo.cpp
@@ -3374,6 +3374,11 @@ inline static bool isDefConvertible(const MachineInstr &MI, bool &NoSignFlag) {
 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: