[WebAssembly] Fix --export of LTO symbols

[ruiu]

LGTM

test/wasm/lto/export.ll

+; RUN: llvm-as -o %t.bc %s
+; RUN: not wasm-ld --export=missing -o %t.wasm %t.bc 2>&1 | FileCheck -check-prefix=CHECK-ERROR %s
+; RUN: wasm-ld --export=hidden_function -o %t.wasm %t.bc
+; RUN: obj2yaml %t.wasm | FileCheck %s
+
+target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
+target triple = "wasm32-unknown-unknown"
+
+define hidden i32 @hidden_function() local_unnamed_addr {
+entry:
+  ret i32 0
+}
+
+define void @_start() local_unnamed_addr {
+entry:
+  ret void
+}
+
+; CHECK-ERROR: error: symbol exported via --export not found: missing
+
+; CHECK:        - Type:            EXPORT
+; CHECK-NEXT:     Exports:
+; CHECK-NEXT:       - Name:            memory
+; CHECK-NEXT:         Kind:            MEMORY
+; CHECK-NEXT:         Index:           0
+; CHECK-NEXT:       - Name:            __heap_base
+; CHECK-NEXT:         Kind:            GLOBAL
+; CHECK-NEXT:         Index:           1
+; CHECK-NEXT:       - Name:            __data_end
+; CHECK-NEXT:         Kind:            GLOBAL
+; CHECK-NEXT:         Index:           2
+; CHECK-NEXT:       - Name:            _start
+; CHECK-NEXT:         Kind:            FUNCTION
+; CHECK-NEXT:         Index:           2
+; CHECK-NEXT:       - Name:            hidden_function
+; CHECK-NEXT:         Kind:            FUNCTION
+; CHECK-NEXT:         Index:           1
+; CHECK-NEXT:   - Type:            CODE

wasm/Driver.cpp

for (InputFile *F : Files)
     Symtab->addFile(F);
   if (errorCount())
     return;
 
   // Add synthetic dummies for weak undefined functions.
   if (!Config->Relocatable)
     handleWeakUndefines();
 
+  // Handle --export.
+  for (auto *Arg : Args.filtered(OPT_export)) {
+    StringRef Name = Arg->getValue();
+    Symbol *Sym = Symtab->find(Name);
+    if (Sym && Sym->isDefined())
+      Sym->ForceExport = true;
+    else if (!Config->AllowUndefined)
+      error("symbol exported via --export not found: " + Name);
+  }
+
   // Do link-time optimization if given files are LLVM bitcode files.
   // This compiles bitcode files into real object files.
   Symtab->addCombinedLTOObject();
   if (errorCount())
     return;
 
   // Make sure we have resolved all symbols.
   if (!Config->Relocatable && !Config->AllowUndefined) {
if (!Config->Relocatable && !Config->AllowUndefined) {
     }
     if (EntrySym && !EntrySym->isDefined())
       error("entry symbol not defined (pass --no-entry to supress): " +
             EntrySym->getName());
   }
   if (errorCount())
     return;
 
-  // Handle --export.
-  for (auto *Arg : Args.filtered(OPT_export)) {
-    StringRef Name = Arg->getValue();
-    Symbol *Sym = Symtab->find(Name);
-    if (Sym && Sym->isDefined())
-      Sym->setHidden(false);
-    else if (!Config->AllowUndefined)
-      error("symbol exported via --export not found: " + Name);
-  }
-
   if (EntrySym)
     EntrySym->setHidden(false);
 
   if (errorCount())
     return;
 
   // Do size optimizations: garbage collection
   markLive();
 
   // Write the result to the file.
   writeResult();
 }

wasm/Symbols.h

public:
   uint32_t getOutputSymbolIndex() const;
   void setOutputSymbolIndex(uint32_t Index);
 
   WasmSymbolType getWasmType() const;
   bool isExported() const;
 
   // True if this symbol was referenced by a regular (non-bitcode) object.
   unsigned IsUsedInRegularObj : 1;
+  unsigned ForceExport : 1;
 
 protected:
   Symbol(StringRef Name, Kind K, uint32_t Flags, InputFile *F)
-      : IsUsedInRegularObj(false), Name(Name), SymbolKind(K), Flags(Flags),
-        File(F), Referenced(!Config->GcSections) {}
+      : IsUsedInRegularObj(false), ForceExport(false), Name(Name),
+        SymbolKind(K), Flags(Flags), File(F), Referenced(!Config->GcSections) {}
 
   StringRef Name;
   Kind SymbolKind;
   uint32_t Flags;
   InputFile *File;
   uint32_t OutputSymbolIndex = INVALID_INDEX;
   bool Referenced;
 };
static_assert(alignof(T) <= alignof(SymbolUnion),
                 "SymbolUnion not aligned enough");
   assert(static_cast<Symbol *>(static_cast<T *>(nullptr)) == nullptr &&
          "Not a Symbol");
 
   Symbol SymCopy = *S;
 
   T *S2 = new (S) T(std::forward<ArgT>(Arg)...);
   S2->IsUsedInRegularObj = SymCopy.IsUsedInRegularObj;
+  S2->ForceExport = SymCopy.ForceExport;
   return S2;
 }
 
 } // namespace wasm
 
 // Returns a symbol name for an error message.
 std::string toString(const wasm::Symbol &Sym);
 std::string toString(wasm::Symbol::Kind Kind);
 
 } // namespace lld
 
 #endif

wasm/Symbols.cpp

void Symbol::setHidden(bool IsHidden) {
   else
     Flags |= WASM_SYMBOL_VISIBILITY_DEFAULT;
 }
 
 bool Symbol::isExported() const {
   if (!isDefined() || isLocal())
     return false;
 
-  if (Config->ExportAll)
+  if (ForceExport || Config->ExportAll)
     return true;
 
   return !isHidden();
 }
 
 uint32_t FunctionSymbol::getFunctionIndex() const {
   if (auto *F = dyn_cast<DefinedFunction>(this))
     return F->Function->getFunctionIndex();