[WebAssembly] Emit type signatures for declared functions

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.

Differential Revision: http://reviews.llvm.org/D20891

Re-apply r271599 but instead of bailing with an error when a declared
function has multiple returns, replace it with a pointer argument. Also
add the test case I forgot to 'git add' last time around.

llvm-svn: 271703

llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.cpp

@@ -64,6 +64,16 @@ void WebAssemblyTargetAsmStreamer::emitLocal(ArrayRef<MVT> 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) {

llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.h

@@ -37,6 +37,12 @@ public:
   virtual void emitLocal(ArrayRef<MVT> Types) = 0;
   /// .endfunc
   virtual void emitEndFunc() = 0;
+  /// .functype
+  virtual void emitIndirectFunctionType(StringRef name,
+                                        SmallVectorImpl<MVT> &SignatureVTs,
+                                        size_t NumResults) {
+    llvm_unreachable("emitIndirectFunctionType not implemented");
+  }
 };
 
 /// This part is for ascii assembly output
@@ -50,6 +56,9 @@ public:
   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

llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp

@@ -67,6 +67,7 @@ private:
   // AsmPrinter Implementation.
   //===------------------------------------------------------------------===//
 
+  void EmitEndOfAsmFile(Module &M) override;
   void EmitJumpTableInfo() override;
   void EmitConstantPool() override;
   void EmitFunctionBodyStart() override;
@@ -124,16 +125,6 @@ WebAssemblyTargetStreamer *WebAssemblyAsmPrinter::getTargetStreamer() {
 //===----------------------------------------------------------------------===//
 // 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());
@@ -150,6 +141,42 @@ static void ComputeLegalValueVTs(const Function &F, const TargetMachine &TM,
   }
 }
 
+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);
+      size_t NumResults = SignatureVTs.size();
+      if (SignatureVTs.size() > 1) {
+        // WebAssembly currently can't lower returns of multiple values without
+        // demoting to sret (see WebAssemblyTargetLowering::CanLowerReturn). So
+        // replace multiple return values with a pointer parameter.
+        SignatureVTs.clear();
+        SignatureVTs.push_back(
+            MVT::getIntegerVT(M.getDataLayout().getPointerSizeInBits()));
+        NumResults = 0;
+      }
+
+      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());

llvm/test/CodeGen/WebAssembly/indirect-import.ll

@@ -0,0 +1,73 @@
+; 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
+
+declare i128 @extern_i128ret(i64) #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, i32
+; CHECK: .functype       extern_i128ret, void, i32, i64