[clang] Add Swift support for MIPS

[colemancda]

Summary

Adds support for compiling Swift targeting the MIPS ABI

[aschwaighofer]

This looks good to me. Can you rebase your patch so that it applies on top of github.com:apple/llvm-project.git main?

[colemancda]

Rebased

clang/lib/Basic/Targets/Mips.h

public:
   bool hasInt128Type() const override {
     return (ABI == "n32" || ABI == "n64") || getTargetOpts().ForceEnableInt128;
   }
 
   unsigned getUnwindWordWidth() const override;
 
   bool validateTarget(DiagnosticsEngine &Diags) const override;
   bool hasBitIntType() const override { return true; }
+
+  CallingConvCheckResult checkCallingConvention(CallingConv CC) const override {
+    switch (CC) {
+    case CC_Swift:
+      return CCCR_OK;
+    case CC_SwiftAsync:
+      return CCCR_Error;
+    default:
+      return CCCR_Warning;
+    }
+  }
 };
 } // namespace targets
 } // namespace clang
 
 #endif // LLVM_CLANG_LIB_BASIC_TARGETS_MIPS_H

clang/lib/CodeGen/TargetInfo.cpp

 }
 
 //===----------------------------------------------------------------------===//
 // MIPS ABI Implementation.  This works for both little-endian and
 // big-endian variants.
 //===----------------------------------------------------------------------===//
 
 namespace {
-class MipsABIInfo : public ABIInfo {
+class MipsABIInfo : public SwiftABIInfo {
   bool IsO32;
   const unsigned MinABIStackAlignInBytes, StackAlignInBytes;
   void CoerceToIntArgs(uint64_t TySize,
                        SmallVectorImpl<llvm::Type *> &ArgList) const;
   llvm::Type* HandleAggregates(QualType Ty, uint64_t TySize) const;
   llvm::Type* returnAggregateInRegs(QualType RetTy, uint64_t Size) const;
   llvm::Type* getPaddingType(uint64_t Align, uint64_t Offset) const;
 public:
-  MipsABIInfo(CodeGenTypes &CGT, bool _IsO32) :
-    ABIInfo(CGT), IsO32(_IsO32), MinABIStackAlignInBytes(IsO32 ? 4 : 8),
+  MipsABIInfo(CodeGenTypes &CGT, bool _IsO32)
+      : SwiftABIInfo(CGT), IsO32(_IsO32),
+        MinABIStackAlignInBytes(IsO32 ? 4 : 8),
         StackAlignInBytes(IsO32 ? 8 : 16) {}
 
   ABIArgInfo classifyReturnType(QualType RetTy) const;
   ABIArgInfo classifyArgumentType(QualType RetTy, uint64_t &Offset) const;
   void computeInfo(CGFunctionInfo &FI) const override;
   Address EmitVAArg(CodeGenFunction &CGF, Address VAListAddr,
                     QualType Ty) const override;
   ABIArgInfo extendType(QualType Ty) const;
+
+private:
+  bool shouldPassIndirectlyForSwift(ArrayRef<llvm::Type *> scalars,
+                                    bool asReturnValue) const override {
+    return occupiesMoreThan(CGT, scalars, /*total*/ 4);
+  }
+
+  bool isSwiftErrorInRegister() const override { return false; }
 };
 
 class MIPSTargetCodeGenInfo : public TargetCodeGenInfo {
   unsigned SizeOfUnwindException;
 public:
   MIPSTargetCodeGenInfo(CodeGenTypes &CGT, bool IsO32)
       : TargetCodeGenInfo(std::make_unique<MipsABIInfo>(CGT, IsO32)),
         SizeOfUnwindException(IsO32 ? 24 : 32) {}