Support Swift calling convention for WebAssembly targets

[kateinoigakukun]

Summary

Support Swift calling convention for WebAssembly targets

This adds basic support for the Swift calling convention with WebAssembly targets.

[sbc100]

clang/lib/Basic/Targets/WebAssembly.h

122

This seems to disagree with the longer list in callingConvSupported. Is this going to generate unnecessary warnings?

[kateinoigakukun]

clang/lib/Basic/Targets/WebAssembly.h

122

By default, checkCallingConvention allows only CC_C due to it's super class implementation. This change just allow to use SwiftCC and there is no effect to other CC.

[dschuff]

Sorry we left this dangling for so long. This little change looks fine; I guess you must be in the process of porting swift to wasm? Do you have any more detailed plans for that written down anywhere, or a prototype you can show?

[kateinoigakukun]

In D71823#1834488, @dschuff wrote:

Sorry we left this dangling for so long. This little change looks fine; I guess you must be in the process of porting swift to wasm? Do you have any more detailed plans for that written down anywhere, or a prototype you can show?

Yes, we are working on wasm porting here. And I'm porting this forked llvm-project into upstream step by step.

[kateinoigakukun]

Could you merge this?

clang/lib/Basic/Targets/WebAssembly.h

private:
   }
 
   IntType getLeastIntTypeByWidth(unsigned BitWidth, bool IsSigned) const final {
     // WebAssembly uses long long for int_least64_t and int_fast64_t.
     return BitWidth == 64
                ? (IsSigned ? SignedLongLong : UnsignedLongLong)
                : TargetInfo::getLeastIntTypeByWidth(BitWidth, IsSigned);
   }
+
+  CallingConvCheckResult checkCallingConvention(CallingConv CC) const override {
+    switch (CC) {
+    case CC_C:
+    case CC_Swift:
+      return CCCR_OK;
+    default:
+      return CCCR_Warning;
+    }
+  }
 };
 class LLVM_LIBRARY_VISIBILITY WebAssembly32TargetInfo
     : public WebAssemblyTargetInfo {
 public:
   explicit WebAssembly32TargetInfo(const llvm::Triple &T,
                                    const TargetOptions &Opts)
       : WebAssemblyTargetInfo(T, Opts) {
     resetDataLayout("e-m:e-p:32:32-i64:64-n32:64-S128");

llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp

static bool callingConvSupported(CallingConv::ID CallConv) {
   // conventions. We don't yet have a way to annotate calls with properties like
   // "cold", and we don't have any call-clobbered registers, so these are mostly
   // all handled the same.
   return CallConv == CallingConv::C || CallConv == CallingConv::Fast ||
          CallConv == CallingConv::Cold ||
          CallConv == CallingConv::PreserveMost ||
          CallConv == CallingConv::PreserveAll ||
          CallConv == CallingConv::CXX_FAST_TLS ||
-         CallConv == CallingConv::WASM_EmscriptenInvoke;
+         CallConv == CallingConv::WASM_EmscriptenInvoke ||
+         CallConv == CallingConv::Swift;
 }
 
 SDValue
 WebAssemblyTargetLowering::LowerCall(CallLoweringInfo &CLI,
                                      SmallVectorImpl<SDValue> &InVals) const {
   SelectionDAG &DAG = CLI.DAG;
   SDLoc DL = CLI.DL;
   SDValue Chain = CLI.Chain;