[llvm] [GlobalIsel] Transform build_vector(binop(_, C), ...) -> binop(bv, constant bv) (PR #73577)

[Thorsten Schütt via llvm-commits]

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@@ -6224,3 +6224,89 @@ void CombinerHelper::applyCommuteBinOpOperands(MachineInstr &MI) {
   MI.getOperand(2).setReg(LHSReg);
   Observer.changedInstr(MI);
 }
+
+// Transform build_vector of binop(_,C) -> binop(BV, constant BV).
+bool CombinerHelper::matchBuildVectorToBinOp(MachineInstr &MI,
+                                             BuildFnTy &MatchInfo) {
+  GBuildVector *BuildVector = cast<GBuildVector>(&MI);
+  Register Dst = BuildVector->getReg(0);
+
+  unsigned NumOfSources = BuildVector->getNumSources();
+  if (NumOfSources == 1)
+    return false;
+
+  LLT ElementTy = MRI.getType(BuildVector->getSourceReg(0));
+  LLT BVTy = MRI.getType(BuildVector->getReg(0));
+
+  MachineInstr *FirstDef = MRI.getVRegDef(BuildVector->getSourceReg(0));
+  const unsigned Opcode = FirstDef->getOpcode();
+  SmallVector<Register> LHS;
+
+  if (isa<GIntBinOp>(FirstDef)) {
+    SmallVector<APInt> RHS;
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tschuett wrote:

There is:
https://github.com/llvm/llvm-project/blob/a05c23fdcf45c39e31931a68f2352a7eff5333a4/llvm/include/llvm/CodeGen/GlobalISel/Utils.h#L196
I thought about that, but it will fail with `buildBuildVectorConstant` . It sometimes must be floats and sometimes it must be integers.

https://github.com/llvm/llvm-project/pull/73577