GlobalISel: Translate llvm.convert.{to|from}.fp16 intrinsics

[arsenm]

Summary

I think these were added as a workaround for SelectionDAG lacking half
legalization support in the past. I think they should probably be
removed from the IR, but clang does still have a target control to
emit these instead of the native half fpext/fptrunc.

[t.p.northover]

LGTM.

[arsenm]

97b5fb78d137a44bec104ba073dd620008ed7abb

llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp

if (TM.Options.AllowFPOpFusion != FPOpFusion::Strict &&
       LLT Ty = getLLTForType(*CI.getType(), *DL);
       auto FMul = MIRBuilder.buildFMul(
           Ty, Op0, Op1, MachineInstr::copyFlagsFromInstruction(CI));
       MIRBuilder.buildFAdd(Dst, FMul, Op2,
                            MachineInstr::copyFlagsFromInstruction(CI));
     }
     return true;
   }
+  case Intrinsic::convert_from_fp16:
+    // FIXME: This intrinsic should probably be removed from the IR.
+    MIRBuilder.buildFPExt(getOrCreateVReg(CI),
+                          getOrCreateVReg(*CI.getArgOperand(0)),
+                          MachineInstr::copyFlagsFromInstruction(CI));
+    return true;
+  case Intrinsic::convert_to_fp16:
+    // FIXME: This intrinsic should probably be removed from the IR.
+    MIRBuilder.buildFPTrunc(getOrCreateVReg(CI),
+                            getOrCreateVReg(*CI.getArgOperand(0)),
+                            MachineInstr::copyFlagsFromInstruction(CI));
+    return true;
   case Intrinsic::memcpy:
   case Intrinsic::memmove:
   case Intrinsic::memset:
     return translateMemFunc(CI, MIRBuilder, ID);
   case Intrinsic::eh_typeid_for: {
     GlobalValue *GV = ExtractTypeInfo(CI.getArgOperand(0));
     Register Reg = getOrCreateVReg(CI);
     unsigned TypeID = MF->getTypeIDFor(GV);

llvm/test/CodeGen/AArch64/GlobalISel/irtranslator-convert-fp16-intrinsics.ll

+; NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
+; RUN: llc -mtriple=aarch64-- -mcpu=falkor -mattr=+lse -O0 -aarch64-enable-atomic-cfg-tidy=0 -stop-after=irtranslator -global-isel -verify-machineinstrs %s -o - | FileCheck %s
+
+define i16 @convert_to_fp16(float %src) {
+  ; CHECK-LABEL: name: convert_to_fp16
+  ; CHECK: bb.1 (%ir-block.0):
+  ; CHECK:   liveins: $s0
+  ; CHECK:   [[COPY:%[0-9]+]]:_(s32) = COPY $s0
+  ; CHECK:   [[FPTRUNC:%[0-9]+]]:_(s16) = G_FPTRUNC [[COPY]](s32)
+  ; CHECK:   [[ANYEXT:%[0-9]+]]:_(s32) = G_ANYEXT [[FPTRUNC]](s16)
+  ; CHECK:   $w0 = COPY [[ANYEXT]](s32)
+  ; CHECK:   RET_ReallyLR implicit $w0
+  %cvt = call i16 @llvm.convert.to.fp16.f32(float %src)
+  ret i16 %cvt
+}
+
+define float @convert_from_fp16(i16 %src) {
+  ; CHECK-LABEL: name: convert_from_fp16
+  ; CHECK: bb.1 (%ir-block.0):
+  ; CHECK:   liveins: $w0
+  ; CHECK:   [[COPY:%[0-9]+]]:_(s32) = COPY $w0
+  ; CHECK:   [[TRUNC:%[0-9]+]]:_(s16) = G_TRUNC [[COPY]](s32)
+  ; CHECK:   [[FPEXT:%[0-9]+]]:_(s32) = G_FPEXT [[TRUNC]](s16)
+  ; CHECK:   $s0 = COPY [[FPEXT]](s32)
+  ; CHECK:   RET_ReallyLR implicit $s0
+  %cvt = call float @llvm.convert.from.fp16.f32(i16 %src)
+  ret float %cvt
+}
+
+declare i16 @llvm.convert.to.fp16.f32(float) nounwind readnone
+declare float @llvm.convert.from.fp16.f32(i16) nounwind readnone