[llvm] [AMDGPU] Recognise bitmask operations as srcmods on select (PR #152119)

[Stanislav Mekhanoshin via llvm-commits]

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@@ -3036,6 +3036,42 @@ bool AMDGPUDAGToDAGISel::SelectVOP3ModsImpl(SDValue In, SDValue &Src,
     Src = Src.getOperand(0);
   }
 
+  // Convert various sign-bit masks on integers to src mods. Currently disabled
+  // for 16-bit types as the codegen replaces the operand without adding a
+  // srcmod. This is intentionally finding the cases where we are performing
+  // float neg and abs on int types, the goal is not to obtain two's complement
+  // neg or abs. Limit converison to select operands via the nonCanonalizing
+  // pattern.
+  // TODO: Add 16-bit support.
+  if (IsCanonicalizing)
+    return true;
+
+  unsigned Opc = Src->getOpcode();
+  EVT VT = Src.getValueType();
+  if ((Opc != ISD::AND && Opc != ISD::OR && Opc != ISD::XOR) ||
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rampitec wrote:

On the previous step it may have selected some modifiers and changed `Src` already. Below the code will check this modified `Src`. I believe it is incorrect. For example it may select NEG twice, when double NEG is a no-op. The easiest way would be to return if modifiers are already selected.

https://github.com/llvm/llvm-project/pull/152119