[llvm] [AMDGPU] expand-fp: Change frem expansion criterion (PR #158285)

[Matt Arsenault via llvm-commits]

================
@@ -74,11 +74,63 @@ class FRemExpander {
   /// Constant 1 of type \p ExTy.
   Value *One;
 
+  /// The frem argument/return types that can be expanded by this class.
+  // TODO The expansion could work for other floating point types
+  // as well, but this would require additional testing.
+  inline static const SmallVector<MVT, 3> ExpandableTypes{MVT::f16, MVT::f32,
+                                                          MVT::f64};
+
+  /// Libcalls for frem instructions of the type at the corresponding
+  /// positions of ExpandableTypes.
+  inline static const SmallVector<RTLIB::Libcall, 3> FremLibcalls{
+      RTLIB::REM_F32, RTLIB::REM_F32, RTLIB::REM_F64};
+
+  /// Return the Libcall for frem instructions of expandable type \p VT or
+  /// std::nullopt if \p VT is not expandable.
+  static std::optional<RTLIB::Libcall> getFremLibcallForType(EVT VT) {
+    auto *It = find(ExpandableTypes, VT.getSimpleVT());
+    if (It == ExpandableTypes.end())
+      return {};
+
+    return FremLibcalls[It - ExpandableTypes.begin()];
+  };
+
 public:
   static bool canExpandType(Type *Ty) {
-    // TODO The expansion should work for other floating point types
-    // as well, but this would require additional testing.
-    return Ty->isIEEELikeFPTy() && !Ty->isBFloatTy() && !Ty->isFP128Ty();
+    EVT VT = EVT::getEVT(Ty);
+    assert(VT.isSimple() && "Can expand only simple types");
+
+    return find(ExpandableTypes, VT.getSimpleVT());
+  }
+
+  /// Return true if the pass should expand a frem instruction of the
+  /// given \p Ty for the target represented by \p TLI. Expansion
+  /// should happen if the legalization for the scalar type uses a
+  /// non-existing libcall.
+  static bool shouldExpandFremType(const TargetLowering &TLI, EVT VT) {
+    TargetLowering::LegalizeAction LA = TLI.getOperationAction(ISD::FREM, VT);
+    if (LA != TargetLowering::LegalizeAction::LibCall &&
+        LA != TargetLowering::LegalizeAction::Expand)
+      return false;
----------------
arsenm wrote:

This should only handle the Expand case, and shouldn't need to consider Libcall. Libcall is what the DAG will emit. If the actions are still specifying expand, they need to change to report libcall 

https://github.com/llvm/llvm-project/pull/158285