[WebAssembly] Add symbol flag to the binary format llvm.used

Summary:
Rather than add a new attribute
See https://github.com/WebAssembly/tool-conventions/issues/64

Subscribers: dschuff, jgravelle-google, aheejin, sunfish, rupprecht, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D57864

llvm-svn: 353360

3 files changed, 7 insertions, 0 deletions

diff --git a/llvm/lib/MC/MCAsmInfoWasm.cpp b/llvm/lib/MC/MCAsmInfoWasm.cpp
index 65a937b7716..ce6ec7ef211 100644
--- a/llvm/lib/MC/MCAsmInfoWasm.cpp
+++ b/llvm/lib/MC/MCAsmInfoWasm.cpp
@@ -18,6 +18,7 @@ void MCAsmInfoWasm::anchor() {}
 
 MCAsmInfoWasm::MCAsmInfoWasm() {
   HasIdentDirective = true;
+  HasNoDeadStrip = true;
   WeakRefDirective = "\t.weak\t";
   PrivateGlobalPrefix = ".L";
   PrivateLabelPrefix = ".L";
diff --git a/llvm/lib/MC/MCWasmStreamer.cpp b/llvm/lib/MC/MCWasmStreamer.cpp
index 36571fce062..86fa7219785 100644
--- a/llvm/lib/MC/MCWasmStreamer.cpp
+++ b/llvm/lib/MC/MCWasmStreamer.cpp
@@ -121,6 +121,10 @@ bool MCWasmStreamer::EmitSymbolAttribute(MCSymbol *S, MCSymbolAttr Attribute) {
   case MCSA_Cold:
     break;
 
+  case MCSA_NoDeadStrip:
+    Symbol->setExported();
+    break;
+
   default:
     // unrecognized directive
     llvm_unreachable("unexpected MCSymbolAttr");
diff --git a/llvm/lib/MC/WasmObjectWriter.cpp b/llvm/lib/MC/WasmObjectWriter.cpp
index b5260bbceae..00d48659890 100644
--- a/llvm/lib/MC/WasmObjectWriter.cpp
+++ b/llvm/lib/MC/WasmObjectWriter.cpp
@@ -1454,6 +1454,8 @@ uint64_t WasmObjectWriter::writeObject(MCAssembler &Asm,
       Flags |= wasm::WASM_SYMBOL_BINDING_LOCAL;
     if (WS.isUndefined())
       Flags |= wasm::WASM_SYMBOL_UNDEFINED;
+    if (WS.isExported())
+      Flags |= wasm::WASM_SYMBOL_EXPORTED;
 
     wasm::WasmSymbolInfo Info;
     Info.Name = WS.getName();