[WebAssembly] Emit type signatures for declared functions

[dschuff]

Summary

Under emscripten, C code can take the address of a function implemented
in Javascript (which is exposed via an import in wasm). Because imports
do not have linear memory address in wasm, we need to generate a thunk
to be the target of the indirect call; it call the import directly.

To make this possible, LLVM needs to emit the type signatures for these
functions, because they may not be called directly or referred to other
than where the address is taken.

This uses s new .s directive (.functype) which specifies the signature.

[dschuff]

• clang-format

[dschuff]

• Add dox comment, fix typo

[sunfish]

Ok, as we discussed on IRC, we may do other things in the future, but for now this looks good.

lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.h

43

This should probably contain an abort so that we don't have a silent difference between a .s file and a .o file.

[dschuff]

• clang-format
• Add dox comment, fix typo
• Add unreachable to catch unimplemented case for non-asm streamer

lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.h

public:
   /// .param
   virtual void emitParam(ArrayRef<MVT> Types) = 0;
   /// .result
   virtual void emitResult(ArrayRef<MVT> Types) = 0;
   /// .local
   virtual void emitLocal(ArrayRef<MVT> Types) = 0;
   /// .endfunc
   virtual void emitEndFunc() = 0;
+  virtual void emitIndirectFunctionType(StringRef name,
+                                        SmallVectorImpl<MVT> &SignatureVTs,
+                                        size_t NumResults) {}
 };
 
 /// This part is for ascii assembly output
 class WebAssemblyTargetAsmStreamer final : public WebAssemblyTargetStreamer {
   formatted_raw_ostream &OS;
 
 public:
   WebAssemblyTargetAsmStreamer(MCStreamer &S, formatted_raw_ostream &OS);
 
   void emitParam(ArrayRef<MVT> Types) override;
   void emitResult(ArrayRef<MVT> Types) override;
   void emitLocal(ArrayRef<MVT> Types) override;
   void emitEndFunc() override;
+  void emitIndirectFunctionType(StringRef name,
+                                SmallVectorImpl<MVT> &SignatureVTs,
+                                size_t NumResults) override;
 };
 
 /// This part is for ELF object output
 class WebAssemblyTargetELFStreamer final : public WebAssemblyTargetStreamer {
 public:
   explicit WebAssemblyTargetELFStreamer(MCStreamer &S);
 
   void emitParam(ArrayRef<MVT> Types) override;
   void emitResult(ArrayRef<MVT> Types) override;
   void emitLocal(ArrayRef<MVT> Types) override;
   void emitEndFunc() override;
 };
 
 } // end namespace llvm
 
 #endif

lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.cpp

 
 void WebAssemblyTargetAsmStreamer::emitLocal(ArrayRef<MVT> Types) {
   OS << "\t.local  \t";
   PrintTypes(OS, Types);
 }
 
 void WebAssemblyTargetAsmStreamer::emitEndFunc() { OS << "\t.endfunc\n"; }
 
+void WebAssemblyTargetAsmStreamer::emitIndirectFunctionType(
+    StringRef name, SmallVectorImpl<MVT> &SignatureVTs, size_t NumResults) {
+  OS << "\t.functype\t" << name;
+  if (NumResults == 0) OS << ", void";
+  for (auto Ty : SignatureVTs) {
+    OS << ", " << WebAssembly::TypeToString(Ty);
+  }
+  OS << "\n";
+}
+
 // FIXME: What follows is not the real binary encoding.
 
 static void EncodeTypes(MCStreamer &Streamer, ArrayRef<MVT> Types) {
   Streamer.EmitIntValue(Types.size(), sizeof(uint64_t));
   for (MVT Type : Types)
     Streamer.EmitIntValue(Type.SimpleTy, sizeof(uint64_t));
 }
 

lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp

bool runOnMachineFunction(MachineFunction &MF) override {
     MFI = MF.getInfo<WebAssemblyFunctionInfo>();
     return AsmPrinter::runOnMachineFunction(MF);
   }
 
   //===------------------------------------------------------------------===//
   // AsmPrinter Implementation.
   //===------------------------------------------------------------------===//
 
+  void EmitEndOfAsmFile(Module &M) override;
   void EmitJumpTableInfo() override;
   void EmitConstantPool() override;
   void EmitFunctionBodyStart() override;
   void EmitFunctionBodyEnd() override;
   void EmitInstruction(const MachineInstr *MI) override;
   const MCExpr *lowerConstant(const Constant *CV) override;
   bool PrintAsmOperand(const MachineInstr *MI, unsigned OpNo,
                        unsigned AsmVariant, const char *ExtraCode,

 WebAssemblyTargetStreamer *WebAssemblyAsmPrinter::getTargetStreamer() {
   MCTargetStreamer *TS = OutStreamer->getTargetStreamer();
   return static_cast<WebAssemblyTargetStreamer *>(TS);
 }
 
 //===----------------------------------------------------------------------===//
 // WebAssemblyAsmPrinter Implementation.
 //===----------------------------------------------------------------------===//
-
-void WebAssemblyAsmPrinter::EmitConstantPool() {
-  assert(MF->getConstantPool()->getConstants().empty() &&
-         "WebAssembly disables constant pools");
-}
-
-void WebAssemblyAsmPrinter::EmitJumpTableInfo() {
-  // Nothing to do; jump tables are incorporated into the instruction stream.
-}
-
 static void ComputeLegalValueVTs(const Function &F, const TargetMachine &TM,
                                  Type *Ty, SmallVectorImpl<MVT> &ValueVTs) {
   const DataLayout &DL(F.getParent()->getDataLayout());
   const WebAssemblyTargetLowering &TLI =
       *TM.getSubtarget<WebAssemblySubtarget>(F).getTargetLowering();
   SmallVector<EVT, 4> VTs;
   ComputeValueVTs(TLI, DL, Ty, VTs);
 
   for (EVT VT : VTs) {
     unsigned NumRegs = TLI.getNumRegisters(F.getContext(), VT);
     MVT RegisterVT = TLI.getRegisterType(F.getContext(), VT);
     for (unsigned i = 0; i != NumRegs; ++i)
       ValueVTs.push_back(RegisterVT);
   }
 }
 
+void WebAssemblyAsmPrinter::EmitEndOfAsmFile(Module &M) {
+  for (const auto &F : M) {
+    // Emit function type info for all undefined functions
+    if (F.isDeclarationForLinker() && !F.isIntrinsic()) {
+      SmallVector<MVT, 4> SignatureVTs;
+      ComputeLegalValueVTs(F, TM, F.getReturnType(), SignatureVTs);
+      if (SignatureVTs.size() > 1) {
+        report_fatal_error(
+            "Import functions with nontrival return types are not supported");
+      }
+      size_t NumResults = SignatureVTs.size();
+      for (auto &Arg : F.args()) {
+        ComputeLegalValueVTs(F, TM, Arg.getType(), SignatureVTs);
+      }
+
+      getTargetStreamer()->emitIndirectFunctionType(F.getName(), SignatureVTs,
+                                                    NumResults);
+    }
+  }
+}
+
+void WebAssemblyAsmPrinter::EmitConstantPool() {
+  assert(MF->getConstantPool()->getConstants().empty() &&
+         "WebAssembly disables constant pools");
+}
+
+void WebAssemblyAsmPrinter::EmitJumpTableInfo() {
+  // Nothing to do; jump tables are incorporated into the instruction stream.
+}
+
 void WebAssemblyAsmPrinter::EmitFunctionBodyStart() {
   if (!MFI->getParams().empty())
     getTargetStreamer()->emitParam(MFI->getParams());
 
   SmallVector<MVT, 4> ResultVTs;
   const Function &F(*MF->getFunction());
   ComputeLegalValueVTs(F, TM, F.getReturnType(), ResultVTs);
 

test/CodeGen/WebAssembly/indirect-import.ll

+; RUN: llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -verify-machineinstrs | FileCheck %s
+; RUN: llc < %s -asm-verbose=false -disable-wasm-fallthrough-return-opt -verify-machineinstrs -fast-isel | FileCheck %s
+
+; ModuleID = 'test/dot_s/indirect-import.c'
+source_filename = "test/dot_s/indirect-import.c"
+target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
+target triple = "wasm32"
+
+%struct.big = type { float, double, i32 }
+
+; Function Attrs: nounwind
+; CHECK: bar:
+define hidden i32 @bar() #0 {
+entry:
+  %fd = alloca float (double)*, align 4
+  %vj = alloca void (i64)*, align 4
+  %v = alloca void ()*, align 4
+  %ijidf = alloca i32 (i64, i32, double, float)*, align 4
+  %vs = alloca void (%struct.big*)*, align 4
+  %s = alloca void (%struct.big*)*, align 4
+
+; CHECK: i32.const       {{.+}}=, extern_fd@FUNCTION
+  store float (double)* @extern_fd, float (double)** %fd, align 4
+; CHECK: i32.const       {{.+}}=, extern_vj@FUNCTION
+  store void (i64)* @extern_vj, void (i64)** %vj, align 4
+  %0 = load void (i64)*, void (i64)** %vj, align 4
+  call void %0(i64 1)
+
+; CHECK: i32.const       {{.+}}=, extern_v@FUNCTION
+  store void ()* @extern_v, void ()** %v, align 4
+  %1 = load void ()*, void ()** %v, align 4
+  call void %1()
+
+; CHECK: i32.const       {{.+}}=, extern_ijidf@FUNCTION
+  store i32 (i64, i32, double, float)* @extern_ijidf, i32 (i64, i32, double, float)** %ijidf, align 4
+  %2 = load i32 (i64, i32, double, float)*, i32 (i64, i32, double, float)** %ijidf, align 4
+  %call = call i32 %2(i64 1, i32 2, double 3.000000e+00, float 4.000000e+00)
+
+; CHECK: i32.const       {{.+}}=, extern_struct@FUNCTION
+  store void (%struct.big*)* @extern_struct, void (%struct.big*)** %vs, align 4
+
+; CHECK: i32.const       {{.+}}=, extern_sret@FUNCTION
+  store void (%struct.big*)* @extern_sret, void (%struct.big*)** %s, align 4
+  %3 = load float (double)*, float (double)** %fd, align 4
+  %4 = ptrtoint float (double)* %3 to i32
+  ret i32 %4
+}
+
+declare float @extern_fd(double) #1
+
+declare void @extern_vj(i64) #1
+
+declare void @extern_v() #1
+
+declare i32 @extern_ijidf(i64, i32, double, float) #1
+
+declare void @extern_struct(%struct.big* byval align 8) #1
+
+declare void @extern_sret(%struct.big* sret) #1
+
+attributes #0 = { nounwind "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="generic" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="generic" "unsafe-fp-math"="false" "use-soft-float"="false" }
+
+
+; CHECK: .functype       extern_fd, f32, f64
+; CHECK: .functype       extern_vj, void, i64
+; CHECK: .functype       extern_v, void
+; CHECK: .functype       extern_ijidf, i32, i64, i32, f64, f32
+; CHECK: .functype       extern_struct, void, i32
+; CHECK: .functype       extern_sret, void, i3