From 66bfbedbdfb98bb3c8fbda9ee839e46b430122d1 Mon Sep 17 00:00:00 2001
From: Dan Gohman <sunfish@mozilla.com>
Date: Fri, 20 Dec 2019 21:44:24 -0800
Subject: [PATCH] [WebAssembly] Support wasm exports with zero-length names.

Zero-length strings are valid export names in WebAssembly, so allow
users to specify them.

Differential Revision: https://reviews.llvm.org/D71793
---
 lld/test/wasm/export-name.ll          | 11 ++++++++++-
 lld/wasm/InputChunks.h                |  4 ++--
 lld/wasm/Writer.cpp                   |  5 ++---
 llvm/include/llvm/BinaryFormat/Wasm.h |  2 +-
 4 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/lld/test/wasm/export-name.ll b/lld/test/wasm/export-name.ll
index 83a8bd9..b02f253 100644
--- a/lld/test/wasm/export-name.ll
+++ b/lld/test/wasm/export-name.ll
@@ -8,6 +8,10 @@ define void @foo() #0 {
     ret void
 }
 
+define void @qux() #1 {
+    ret void
+}
+
 define void @_start() {
     call void @foo()
     ret void
@@ -15,6 +19,8 @@ define void @_start() {
 
 attributes #0 = { "wasm-export-name"="bar" }
 
+attributes #1 = { "wasm-export-name"="" }
+
 ; CHECK:       - Type:            EXPORT
 ; CHECK-NEXT:    Exports:
 ; CHECK-NEXT:      - Name:            memory
@@ -23,6 +29,9 @@ attributes #0 = { "wasm-export-name"="bar" }
 ; CHECK-NEXT:      - Name:            bar
 ; CHECK-NEXT:        Kind:            FUNCTION
 ; CHECK-NEXT:        Index:           0
-; CHECK-NEXT:      - Name:            _start
+; CHECK-NEXT:      - Name:            ''
 ; CHECK-NEXT:        Kind:            FUNCTION
 ; CHECK-NEXT:        Index:           1
+; CHECK-NEXT:      - Name:            _start
+; CHECK-NEXT:        Kind:            FUNCTION
+; CHECK-NEXT:        Index:           2
diff --git a/lld/wasm/InputChunks.h b/lld/wasm/InputChunks.h
index 030c9a9..cadff68 100644
--- a/lld/wasm/InputChunks.h
+++ b/lld/wasm/InputChunks.h
@@ -130,8 +130,8 @@ public:
   void writeTo(uint8_t *sectionStart) const override;
   StringRef getName() const override { return function->SymbolName; }
   StringRef getDebugName() const override { return function->DebugName; }
-  StringRef getExportName() const {
-    return function ? function->ExportName : "";
+  llvm::Optional<StringRef> getExportName() const {
+    return function ? function->ExportName : llvm::Optional<StringRef>();
   }
   uint32_t getComdat() const override { return function->Comdat; }
   uint32_t getFunctionInputOffset() const { return getInputSectionOffset(); }
diff --git a/lld/wasm/Writer.cpp b/lld/wasm/Writer.cpp
index ca0bfef..9f4b6ad 100644
--- a/lld/wasm/Writer.cpp
+++ b/lld/wasm/Writer.cpp
@@ -520,9 +520,8 @@ void Writer::calculateExports() {
     StringRef name = sym->getName();
     WasmExport export_;
     if (auto *f = dyn_cast<DefinedFunction>(sym)) {
-      StringRef exportName = f->function->getExportName();
-      if (!exportName.empty()) {
-        name = exportName;
+      if (Optional<StringRef> exportName = f->function->getExportName()) {
+        name = *exportName;
       }
       export_ = {name, WASM_EXTERNAL_FUNCTION, f->getFunctionIndex()};
     } else if (auto *g = dyn_cast<DefinedGlobal>(sym)) {
diff --git a/llvm/include/llvm/BinaryFormat/Wasm.h b/llvm/include/llvm/BinaryFormat/Wasm.h
index e39760e..dd743db 100644
--- a/llvm/include/llvm/BinaryFormat/Wasm.h
+++ b/llvm/include/llvm/BinaryFormat/Wasm.h
@@ -132,7 +132,7 @@ struct WasmFunction {
   uint32_t CodeSectionOffset;
   uint32_t Size;
   uint32_t CodeOffset;  // start of Locals and Body
-  StringRef ExportName; // from the "export" section
+  Optional<StringRef> ExportName; // from the "export" section
   StringRef SymbolName; // from the "linking" section
   StringRef DebugName;  // from the "name" section
   uint32_t Comdat;      // from the "comdat info" section
-- 
2.7.4