[llvm] [AArch64][GlobalISel] Use GPR for illegal fconstants and extend < 32 bit GPR constants to 32 bits (PR #178692)

[David Green via llvm-commits]

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@@ -358,12 +359,77 @@ AArch64RegisterBankInfo::getInstrAlternativeMappings(
   return RegisterBankInfo::getInstrAlternativeMappings(MI);
 }
 
+static bool isLegalFPImm(const MachineInstr &MI, const MachineRegisterInfo &MRI,
+                         const AArch64Subtarget &STI) {
+  assert(MI.getOpcode() == TargetOpcode::G_FCONSTANT);
+  Register Dst = MI.getOperand(0).getReg();
+  LLT Ty = MRI.getType(Dst);
+  if (!Ty.isScalar())
+    return false;
+
+  unsigned Bits = Ty.getSizeInBits();
+  if (Bits != 16 && Bits != 32 && Bits != 64)
+    return false;
+
+  EVT VT = EVT::getFloatingPointVT(Bits);
+  bool OptForSize = MI.getMF()->getFunction().hasOptSize() ||
+                    MI.getMF()->getFunction().hasMinSize();
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davemgreen wrote:

Can we use shouldOptimizeForSize.

https://github.com/llvm/llvm-project/pull/178692