[clang] Added Swift support for RISCV

[colemancda]

Summary

Adds support for compiling Swift targeting the RISCV ABI

[asb]

First of all, thanks for the contribution.

I've not looked at all into the Swift calling convention requirements, but at a minimum this patch is going to need test coverage. I also think RV32 should be handled somehow - either by adding equivalent support, or at least erroring if that's not possible.

[colemancda]

RV32 is enabled as well. I'll add unit tests.

[asb]

In D137309#3914494, @colemancda wrote:

RV32 is enabled as well. I'll add unit tests.

Great, thanks. Is it really the case that shouldPassIndirectlyForSwift has the same result regardless of native word size?

[colemancda]

In D137309#3914550, @asb wrote:

In D137309#3914494, @colemancda wrote:

RV32 is enabled as well. I'll add unit tests.

Great, thanks. Is it really the case that shouldPassIndirectlyForSwift has the same result regardless of native word size?

Yes, if you check other implementations like Arm and AArch64, the implementation is the same.
Where is a good place to start for the unit test development for this ABI?

[jrtc27]

clang/lib/CodeGen/TargetInfo.cpp

10557

Huh? This is unused.

10601

The argument's called maxAllRegisters?

[craig.topper]

clang/lib/CodeGen/TargetInfo.cpp

10555

SwiftABIInfo doesn't inherit from ABIInfo and hasn't since August last year. D130394

clang/lib/Basic/Targets/RISCV.h

initFeatureMap(llvm::StringMap<bool> &Features, DiagnosticsEngine &Diags,
                  const std::vector<std::string> &FeaturesVec) const override;
 
   bool hasFeature(StringRef Feature) const override;
 
   bool handleTargetFeatures(std::vector<std::string> &Features,
                             DiagnosticsEngine &Diags) override;
 
   bool hasExtIntType() 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;
+    }
+  }
 };
+
 class LLVM_LIBRARY_VISIBILITY RISCV32TargetInfo : public RISCVTargetInfo {
 public:
   RISCV32TargetInfo(const llvm::Triple &Triple, const TargetOptions &Opts)
       : RISCVTargetInfo(Triple, Opts) {
     IntPtrType = SignedInt;
     PtrDiffType = SignedInt;
     SizeType = UnsignedInt;
     resetDataLayout("e-m:e-p:32:32-i64:64-n32-S128");

clang/lib/CodeGen/TargetInfo.cpp

static bool getTypeString(SmallStringEnc &Enc, const Decl *D,
   return false;
 }
 
 //===----------------------------------------------------------------------===//
 // RISCV ABI Implementation
 //===----------------------------------------------------------------------===//
 
 namespace {
-class RISCVABIInfo : public DefaultABIInfo {
+class RISCVABIInfo : public SwiftABIInfo {
 private:
+  DefaultABIInfo defaultInfo;
   // Size of the integer ('x') registers in bits.
   unsigned XLen;
   // Size of the floating point ('f') registers in bits. Note that the target
   // ISA might have a wider FLen than the selected ABI (e.g. an RV32IF target
   // with soft float ABI has FLen==0).
   unsigned FLen;
   static const int NumArgGPRs = 8;
   static const int NumArgFPRs = 8;
   bool detectFPCCEligibleStructHelper(QualType Ty, CharUnits CurOff,
                                       llvm::Type *&Field1Ty,
                                       CharUnits &Field1Off,
                                       llvm::Type *&Field2Ty,
                                       CharUnits &Field2Off) const;
 
 public:
   RISCVABIInfo(CodeGen::CodeGenTypes &CGT, unsigned XLen, unsigned FLen)
-      : DefaultABIInfo(CGT), XLen(XLen), FLen(FLen) {}
+      : SwiftABIInfo(CGT), defaultInfo(CGT), XLen(XLen), FLen(FLen) {}
 
   // DefaultABIInfo's classifyReturnType and classifyArgumentType are
   // non-virtual, but computeInfo is virtual, so we overload it.
   void computeInfo(CGFunctionInfo &FI) const override;
 
   ABIArgInfo classifyArgumentType(QualType Ty, bool IsFixed, int &ArgGPRsLeft,
                                   int &ArgFPRsLeft) const;
   ABIArgInfo classifyReturnType(QualType RetTy) const;
 
   Address EmitVAArg(CodeGenFunction &CGF, Address VAListAddr,
                     QualType Ty) const override;
 
   ABIArgInfo extendType(QualType Ty) const;
 
   bool detectFPCCEligibleStruct(QualType Ty, llvm::Type *&Field1Ty,
                                 CharUnits &Field1Off, llvm::Type *&Field2Ty,
                                 CharUnits &Field2Off, int &NeededArgGPRs,
                                 int &NeededArgFPRs) const;
   ABIArgInfo coerceAndExpandFPCCEligibleStruct(llvm::Type *Field1Ty,
                                                CharUnits Field1Off,
                                                llvm::Type *Field2Ty,
                                                CharUnits Field2Off) const;
+
+private:
+  bool shouldPassIndirectlyForSwift(ArrayRef<llvm::Type *> scalars,
+                                    bool asReturnValue) const override {
+    return occupiesMoreThan(CGT, scalars, /*total*/ 4);
+  }
+
+  bool isSwiftErrorInRegister() const override { return false; }
 };
 } // end anonymous namespace
 
 void RISCVABIInfo::computeInfo(CGFunctionInfo &FI) const {
   QualType RetTy = FI.getReturnType();
   if (!getCXXABI().classifyReturnType(FI))
     FI.getReturnInfo() = classifyReturnType(RetTy);
 

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

SDValue RISCVTargetLowering::LowerFormalArguments(
     SelectionDAG &DAG, SmallVectorImpl<SDValue> &InVals) const {
 
   MachineFunction &MF = DAG.getMachineFunction();
 
   switch (CallConv) {
   default:
     report_fatal_error("Unsupported calling convention");
   case CallingConv::C:
+  case CallingConv::Swift:
+  case CallingConv::SwiftTail:
   case CallingConv::Fast:
     break;
   case CallingConv::GHC:
     if (!MF.getSubtarget().getFeatureBits()[RISCV::FeatureStdExtF] ||
         !MF.getSubtarget().getFeatureBits()[RISCV::FeatureStdExtD])
       report_fatal_error(
         "GHC calling convention requires the F and D instruction set extensions");
   }