[llvm] [GlobalIsel] Canonicalize G_FCMP (PR #108891)

[Thorsten Schütt via llvm-commits]

================
@@ -2008,3 +2008,43 @@ llvm::GIConstant::getConstant(Register Const, const MachineRegisterInfo &MRI) {
 
   return GIConstant(MayBeConstant->Value, GIConstantKind::Scalar);
 }
+
+APFloat llvm::GFConstant::getScalarValue() const {
+  assert(Kind == GFConstantKind::Scalar && "Expected scalar constant");
+
+  return Values[0];
+}
+
+std::optional<GFConstant>
+llvm::GFConstant::getConstant(Register Const, const MachineRegisterInfo &MRI) {
+  MachineInstr *Constant = getDefIgnoringCopies(Const, MRI);
+
+  if (GSplatVector *Splat = dyn_cast<GSplatVector>(Constant)) {
+    std::optional<FPValueAndVReg> MayBeConstant =
+        getFConstantVRegValWithLookThrough(Splat->getScalarReg(), MRI);
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tschuett wrote:

There are new look-throughs with APFloat this time.

https://github.com/llvm/llvm-project/pull/108891