[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

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.cpp b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.cpp
index 789a176155b..3d61c15717b 100644
--- a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.cpp
+++ b/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) {