[WebAssembly] Add new `export_name` clang attribute for controlling wasm export names

This is equivalent to the existing `import_name` and `import_module`
attributes which control the import names in the final wasm binary
produced by lld.

This maps the existing

This attribute currently requires a string rather than using the
symbol name for a couple of reasons:

1. Avoid confusion with static and dynamic linking which is
   based on symbol name.  Exporting a function from a wasm module using
   this directive is orthogonal to both static and dynamic linking.
2. Avoids name mangling.

Differential Revision: https://reviews.llvm.org/D70520

4 files changed, 36 insertions, 1 deletions

diff --git a/llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp b/llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp
index 138ce85a23f..1f0bdde0c93 100644
--- a/llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp
+++ b/llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp
@@ -712,6 +712,18 @@ public:
       return expect(AsmToken::EndOfStatement, "EOL");
     }
 
+    if (DirectiveID.getString() == ".export_name") {
+      auto SymName = expectIdent();
+      if (SymName.empty())
+        return true;
+      if (expect(AsmToken::Comma, ","))
+        return true;
+      auto ExportName = expectIdent();
+      auto WasmSym = cast<MCSymbolWasm>(Ctx.getOrCreateSymbol(SymName));
+      WasmSym->setExportName(ExportName);
+      TOut.emitExportName(WasmSym, ExportName);
+    }
+
     if (DirectiveID.getString() == ".import_module") {
       auto SymName = expectIdent();
       if (SymName.empty())
diff --git a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.cpp b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.cpp
index 40926201931..7c21ed5f974 100644
--- a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.cpp
+++ b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.cpp
@@ -94,6 +94,12 @@ void WebAssemblyTargetAsmStreamer::emitImportName(const MCSymbolWasm *Sym,
                            << ImportName << '\n';
 }
 
+void WebAssemblyTargetAsmStreamer::emitExportName(const MCSymbolWasm *Sym,
+                                                  StringRef ExportName) {
+  OS << "\t.export_name\t" << Sym->getName() << ", "
+                           << ExportName << '\n';
+}
+
 void WebAssemblyTargetAsmStreamer::emitIndIdx(const MCExpr *Value) {
   OS << "\t.indidx  \t" << *Value << '\n';
 }
diff --git a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.h b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.h
index 0164f8e572e..9aee1a06c95 100644
--- a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.h
+++ b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyTargetStreamer.h
@@ -48,6 +48,9 @@ public:
   /// .import_name
   virtual void emitImportName(const MCSymbolWasm *Sym,
                               StringRef ImportName) = 0;
+  /// .export_name
+  virtual void emitExportName(const MCSymbolWasm *Sym,
+                              StringRef ExportName) = 0;
 
 protected:
   void emitValueType(wasm::ValType Type);
@@ -68,6 +71,7 @@ public:
   void emitEventType(const MCSymbolWasm *Sym) override;
   void emitImportModule(const MCSymbolWasm *Sym, StringRef ImportModule) override;
   void emitImportName(const MCSymbolWasm *Sym, StringRef ImportName) override;
+  void emitExportName(const MCSymbolWasm *Sym, StringRef ExportName) override;
 };
 
 /// This part is for Wasm object output
@@ -85,6 +89,8 @@ public:
                         StringRef ImportModule) override {}
   void emitImportName(const MCSymbolWasm *Sym,
                       StringRef ImportName) override {}
+  void emitExportName(const MCSymbolWasm *Sym,
+                      StringRef ExportName) override {}
 };
 
 /// This part is for null output
@@ -101,6 +107,7 @@ public:
   void emitEventType(const MCSymbolWasm *) override {}
   void emitImportModule(const MCSymbolWasm *, StringRef) override {}
   void emitImportName(const MCSymbolWasm *, StringRef) override {}
+  void emitExportName(const MCSymbolWasm *, StringRef) override {}
 };
 
 } // end namespace llvm
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
index 5d8b873ce23..cb95d5dbfc0 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp
@@ -96,8 +96,11 @@ void WebAssemblyAsmPrinter::EmitEndOfAsmFile(Module &M) {
   }
 
   for (const auto &F : M) {
+    if (F.isIntrinsic())
+      continue;
+
     // Emit function type info for all undefined functions
-    if (F.isDeclarationForLinker() && !F.isIntrinsic()) {
+    if (F.isDeclarationForLinker()) {
       SmallVector<MVT, 4> Results;
       SmallVector<MVT, 4> Params;
       computeSignatureVTs(F.getFunctionType(), F, TM, Params, Results);
@@ -130,6 +133,13 @@ void WebAssemblyAsmPrinter::EmitEndOfAsmFile(Module &M) {
         getTargetStreamer()->emitImportName(Sym, Name);
       }
     }
+
+    if (F.hasFnAttribute("wasm-export-name")) {
+      auto *Sym = cast<MCSymbolWasm>(getSymbol(&F));
+      StringRef Name = F.getFnAttribute("wasm-export-name").getValueAsString();
+      Sym->setExportName(Name);
+      getTargetStreamer()->emitExportName(Sym, Name);
+    }
   }
 
   for (const auto &G : M.globals()) {