[llvm] [AMDGPU] [GlobalIsel] Combine Fmul with Select into ldexp instruction. (PR #120104)

[Jay Foad via llvm-commits]

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@@ -445,3 +452,67 @@ void AMDGPUCombinerHelper::applyExpandPromotedF16FMed3(MachineInstr &MI,
   Builder.buildFMinNumIEEE(MI.getOperand(0), B1, C1);
   MI.eraseFromParent();
 }
+
+bool AMDGPUCombinerHelper::matchCombineFmulWithSelectToFldexp(
+    MachineInstr &MI, MachineInstr &Sel,
+    std::function<void(MachineIRBuilder &)> &MatchInfo) {
+  assert(MI.getOpcode() == TargetOpcode::G_FMUL);
+  assert(Sel.getOpcode() == TargetOpcode::G_SELECT);
+  assert(MI.getOperand(2).getReg() == Sel.getOperand(0).getReg());
+
+  Register Dst = MI.getOperand(0).getReg();
+  LLT DestTy = MRI.getType(Dst);
+  LLT ScalarDestTy = DestTy.getScalarType();
+
+  if ((ScalarDestTy != LLT::float64() && ScalarDestTy != LLT::float32() &&
+       ScalarDestTy != LLT::float16()) ||
+      (!MRI.hasOneNonDBGUse(Sel.getOperand(0).getReg())))
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jayfoad wrote:

Nit: don't need parentheses around `!MRI.has...`

https://github.com/llvm/llvm-project/pull/120104