[llvm] [AMDGPU] Recognise bitmask operations as srcmods (PR #149110)

[Chris Jackson via llvm-commits]

================
@@ -3036,6 +3036,36 @@ bool AMDGPUDAGToDAGISel::SelectVOP3ModsImpl(SDValue In, SDValue &Src,
     Src = Src.getOperand(0);
   }
 
+  // Convert various sign-bit masks to src mods. Currently disabled for 16-bit
+  // types as the codegen replaces the operand without adding a srcmod.
+  // Recognise (xor a, 0x80000000) as NEG SrcMod.
+  if (Src->getOpcode() == ISD::XOR &&
+      Src.getValueType().getFixedSizeInBits() != 16)
----------------
chrisjbris wrote:

I attempted with the 16-bit versions and I wasn't getting src mods applied. However I take your point about the positive checks, thanks.

https://github.com/llvm/llvm-project/pull/149110