[GlobalISel][AArch64] Add libcall lowering for fpowi. (#67114)

This adds legalization, notably libcall lowering for fpowi. It is a
little different to other methods as the function takes both a float and
integer register. Otherwise all vectors get scalarized and fp16 is
promoted to fp32.

Author: davemgreen

llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp

@@ -532,6 +532,8 @@ static RTLIB::Libcall getRTLibDesc(unsigned Opcode, unsigned Size) {
     RTLIBCASE(REM_F);
   case TargetOpcode::G_FPOW:
     RTLIBCASE(POW_F);
+  case TargetOpcode::G_FPOWI:
+    RTLIBCASE(POWI_F);
   case TargetOpcode::G_FMA:
     RTLIBCASE(FMA_F);
   case TargetOpcode::G_FSIN:
@@ -1014,6 +1016,27 @@ LegalizerHelper::libcall(MachineInstr &MI, LostDebugLocObserver &LocObserver) {
       return Status;
     break;
   }
+  case TargetOpcode::G_FPOWI: {
+    LLT LLTy = MRI.getType(MI.getOperand(0).getReg());
+    unsigned Size = LLTy.getSizeInBits();
+    Type *HLTy = getFloatTypeForLLT(Ctx, LLTy);
+    Type *ITy = IntegerType::get(
+        Ctx, MRI.getType(MI.getOperand(2).getReg()).getSizeInBits());
+    if (!HLTy || (Size != 32 && Size != 64 && Size != 80 && Size != 128)) {
+      LLVM_DEBUG(dbgs() << "No libcall available for type " << LLTy << ".\n");
+      return UnableToLegalize;
+    }
+    auto Libcall = getRTLibDesc(MI.getOpcode(), Size);
+    std::initializer_list<CallLowering::ArgInfo> Args = {
+        {MI.getOperand(1).getReg(), HLTy, 0},
+        {MI.getOperand(2).getReg(), ITy, 1}};
+    LegalizeResult Status =
+        createLibcall(MIRBuilder, Libcall, {MI.getOperand(0).getReg(), HLTy, 0},
+                      Args, LocObserver, &MI);
+    if (Status != Legalized)
+      return Status;
+    break;
+  }
   case TargetOpcode::G_FPEXT:
   case TargetOpcode::G_FPTRUNC: {
     Type *FromTy = getFloatTypeForLLT(Ctx,  MRI.getType(MI.getOperand(1).getReg()));
@@ -4557,6 +4580,8 @@ LegalizerHelper::fewerElementsVector(MachineInstr &MI, unsigned TypeIdx,
     return fewerElementsVectorReductions(MI, TypeIdx, NarrowTy);
   case G_SHUFFLE_VECTOR:
     return fewerElementsVectorShuffle(MI, TypeIdx, NarrowTy);
+  case G_FPOWI:
+    return fewerElementsVectorMultiEltType(GMI, NumElts, {2 /*pow*/});
   default:
     return UnableToLegalize;
   }

llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.cpp

@@ -282,6 +282,10 @@ AArch64LegalizerInfo::AArch64LegalizerInfo(const AArch64Subtarget &ST)
       // Regardless of FP16 support, widen 16-bit elements to 32-bits.
       .minScalar(0, s32)
       .libcallFor({s32, s64});
+  getActionDefinitionsBuilder(G_FPOWI)
+      .scalarize(0)
+      .minScalar(0, s32)
+      .libcallFor({{s32, s32}, {s64, s32}});
 
   getActionDefinitionsBuilder(G_INSERT)
       .legalIf(all(typeInSet(0, {s32, s64, p0}),

llvm/test/CodeGen/AArch64/GlobalISel/legalizer-info-validation.mir

@@ -463,8 +463,8 @@
 # DEBUG-NEXT: .. the first uncovered type index: 1, OK
 # DEBUG-NEXT: .. the first uncovered imm index: 0, OK
 # DEBUG-NEXT: G_FPOWI (opcode {{[0-9]+}}): 2 type indices, 0 imm indices
-# DEBUG-NEXT:.. type index coverage check SKIPPED: no rules defined
-# DEBUG-NEXT:.. imm index coverage check SKIPPED: no rules defined
+# DEBUG-NEXT: .. the first uncovered type index: 2, OK
+# DEBUG-NEXT: .. the first uncovered imm index: 0, OK
 # DEBUG-NEXT: G_FEXP (opcode {{[0-9]+}}): 1 type index, 0 imm indices
 # DEBUG-NEXT: .. opcode {{[0-9]+}} is aliased to {{[0-9]+}}
 # DEBUG-NEXT: .. the first uncovered type index: 1, OK