[llvm] [GlobalISel][ARM] Legalize reset_fpmode (PR #115859)

[Serge Pavlov via llvm-commits]

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@@ -467,6 +468,18 @@ bool ARMLegalizerInfo::legalizeCustom(LegalizerHelper &Helper, MachineInstr &MI,
     MIRBuilder.buildSetFPEnv(NewFPSCR);
     break;
   }
+  case G_RESET_FPMODE: {
+    // To get the default FP mode all control bits are cleared:
+    // FPSCR = FPSCR & (FPStatusBits | FPReservedBits)
+    LLT FPEnvTy = LLT::scalar(32);
+    auto FPEnv = MRI.createGenericVirtualRegister(FPEnvTy);
+    MIRBuilder.buildInstr(G_GET_FPENV).addDef({FPEnv});
+    auto NotModeBitMask = MIRBuilder.buildConstant(
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spavloff wrote:

The G_CONSTANT is illegal. When legalizer creates it in `legalizeInstrStep`, the object of type `LegalizerWorkListManager` adds this instruction to its worklist, and it will be subjected to legalization in next iterations of the legalization in `legalizeMachineFunction`.

https://github.com/llvm/llvm-project/pull/115859