[AArch64][GlobalISel] Expand handling for sitofp and uitofp (#71282)

Similar to #70635, this expands the handling of integer to fp
conversions. The code is very similar to the float->integer conversions
with types handled oppositely. There are some extra unhandled cases
which require more handling for ASR operations.

Author: davemgreen

llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp

@@ -5126,7 +5126,9 @@ LegalizerHelper::moreElementsVector(MachineInstr &MI, unsigned TypeIdx,
   case TargetOpcode::G_FPTRUNC:
   case TargetOpcode::G_FPEXT:
   case TargetOpcode::G_FPTOSI:
-  case TargetOpcode::G_FPTOUI: {
+  case TargetOpcode::G_FPTOUI:
+  case TargetOpcode::G_SITOFP:
+  case TargetOpcode::G_UITOFP: {
     if (TypeIdx != 0)
       return UnableToLegalize;
     Observer.changingInstr(MI);

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

@@ -673,10 +673,33 @@ AArch64LegalizerInfo::AArch64LegalizerInfo(const AArch64Subtarget &ST)
 
   getActionDefinitionsBuilder({G_SITOFP, G_UITOFP})
       .legalForCartesianProduct({s32, s64, v2s64, v4s32, v2s32})
+      .legalIf([=](const LegalityQuery &Query) {
+        return HasFP16 &&
+               (Query.Types[0] == s16 || Query.Types[0] == v4s16 ||
+                Query.Types[0] == v8s16) &&
+               (Query.Types[1] == s32 || Query.Types[1] == s64 ||
+                Query.Types[1] == v4s16 || Query.Types[1] == v8s16);
+      })
+      .widenScalarToNextPow2(1)
       .clampScalar(1, s32, s64)
-      .minScalarSameAs(1, 0)
-      .clampScalar(0, s32, s64)
-      .widenScalarToNextPow2(0);
+      .widenScalarToNextPow2(0)
+      .clampScalarOrElt(0, MinFPScalar, s64)
+      .moreElementsToNextPow2(0)
+      .widenScalarIf(
+          [=](const LegalityQuery &Query) {
+            return Query.Types[0].getScalarSizeInBits() <
+                   Query.Types[1].getScalarSizeInBits();
+          },
+          LegalizeMutations::changeElementSizeTo(0, 1))
+      .widenScalarIf(
+          [=](const LegalityQuery &Query) {
+            return Query.Types[0].getScalarSizeInBits() >
+                   Query.Types[1].getScalarSizeInBits();
+          },
+          LegalizeMutations::changeElementSizeTo(1, 0))
+      .clampNumElements(0, v4s16, v8s16)
+      .clampNumElements(0, v2s32, v4s32)
+      .clampMaxNumElements(0, s64, 2);
 
   // Control-flow
   getActionDefinitionsBuilder(G_BRCOND)