[llvm] Add PreLegalizer pattern matching for degrees GL extension (PR #216506)

[Kaitlin Peng via llvm-commits]

================
@@ -381,3 +381,53 @@ void SPIRVCombinerHelper::applyMatrixMultiply(MachineInstr &MI) const {
     Builder.buildBuildVector(ResReg, ResultScalars);
   MI.eraseFromParent();
 }
+
+bool SPIRVCombinerHelper::matchDegrees(MachineInstr &MI) const {
+  if (MI.getOpcode() != TargetOpcode::G_FMUL)
+    return false;
+  Register Op1 = MI.getOperand(1).getReg();
+  Register Op2 = MI.getOperand(2).getReg();
+  MachineInstr *Op1Def = MRI.getVRegDef(Op1);
+  MachineInstr *Op2Def = MRI.getVRegDef(Op2);
+
+  if (!Op1Def || !Op2Def)
+    return false;
+
+  if (Op1Def->getOpcode() != TargetOpcode::G_FCONSTANT &&
+      Op2Def->getOpcode() != TargetOpcode::G_FCONSTANT)
+    return false;
+
+  MachineInstr *constantMachineInstruction =
+      (Op1Def->getOpcode() == TargetOpcode::G_FCONSTANT) ? Op1Def : Op2Def;
+  MachineOperand &ConstantOperand = constantMachineInstruction->getOperand(1);
+
+  if (!ConstantOperand.isFPImm())
+    return false;
+
+  const ConstantFP *Constant = ConstantOperand.getFPImm();
+  const APFloat &Val = Constant->getValueAPF();
+
+  APFloat Expected(180.0 / llvm::numbers::pi);
+  bool LostInfo = false;
+  Expected.convert(Val.getSemantics(), APFloat::rmNearestTiesToEven, &LostInfo);
+
+  if (Expected.compare(Val) != APFloat::cmpEqual)
+    return false;
+
+  return true;
----------------
kmpeng wrote:

In general, `matchDegrees` is too complicated for what it's supposed to be matching and you're double checking a lot of conditions. If you use `mi_match` your code should become much simpler. Look at the distance and faceforward matchers for reference.

https://github.com/llvm/llvm-project/pull/216506