[WebAssembly] Fix signatures of undefined function in LTO object which are not called directly.

[sbc100]

Summary

We recently added special handling for function that are not called
directly but failed to add testing for the LTO case.

See https://reviews.llvm.org/D62153

[sbc100]

• revert

[ruiu]

LGTM

lld/test/wasm/lto/undef.ll

 ; RUN: llvm-as %s -o %t.o
 ; RUN: wasm-ld %t.o -o %t.wasm --allow-undefined
 ; RUN: obj2yaml %t.wasm | FileCheck %s
 
 target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
 target triple = "wasm32-unknown-unknown"
 
-declare void @bar()
+declare i32 @bar()
+
+; Symbols such as foo which are only called indirectly are handled slightly
+; differently with resepect to signature checking.
+declare i32 @foo()
+
+@ptr = global i8* bitcast (i32 ()* @foo to i8*), align 8
+; Ensure access to ptr is not inlined below, even under LTO
[e-mail] = appending global [1 x i8**] [i8** @ptr], section "llvm.metadata"
 
 define void @_start() {
-  call void @bar()
+  call i32 @bar()
+
+  %addr = load i32 ()*, i32 ()** bitcast (i8** @ptr to i32 ()**), align 8
+  call i32 %addr()
+
   ret void
 }
 
 ; CHECK:       - Type:            IMPORT
 ; CHECK-NEXT:    Imports:         
 ; CHECK-NEXT:      - Module:          env
 ; CHECK-NEXT:        Field:           bar
 ; CHECK-NEXT:        Kind:            FUNCTION
 ; CHECK-NEXT:        SigIndex:        0
+; CHECK-NEXT:      - Module:          env
+; CHECK-NEXT:        Field:           foo
+; CHECK-NEXT:        Kind:            FUNCTION
+; CHECK-NEXT:        SigIndex:        0

lld/wasm/SymbolTable.cpp

error("symbol type mismatch: " + toString(*Existing) + "\n>>> defined as " +
         " in " + toString(File));
 }
 
 // Check the type of new symbol matches that of the symbol is replacing.
 // Returns true if the function types match, false is there is a singature
 // mismatch.
 static bool signatureMatches(FunctionSymbol *Existing,
                              const WasmSignature *NewSig) {
-  if (!NewSig)
-    return true;
-
   const WasmSignature *OldSig = Existing->Signature;
-  if (!OldSig) {
-    Existing->Signature = NewSig;
+
+  // If either function is missing a signature (this happend for bitcode
+  // symbols) then assume they match.  Any mismatch will be reported later
+  // when the LTO objects are added.
+  if (!NewSig || !OldSig)
     return true;
-  }
 
   return *NewSig == *OldSig;
 }
 
 static void checkGlobalType(const Symbol *Existing, const InputFile *File,
                             const WasmGlobalType *NewType) {
   if (!isa<GlobalSymbol>(Existing)) {
     reportTypeError(Existing, File, WASM_SYMBOL_TYPE_GLOBAL);
Symbol *SymbolTable::addDefinedEvent(StringRef Name, uint32_t Flags,
   return S;
 }
 
 Symbol *SymbolTable::addUndefinedFunction(StringRef Name, StringRef ImportName,
                                           StringRef ImportModule,
                                           uint32_t Flags, InputFile *File,
                                           const WasmSignature *Sig,
                                           bool IsCalledDirectly) {
-  LLVM_DEBUG(dbgs() << "addUndefinedFunction: " << Name <<
-             " [" << (Sig ? toString(*Sig) : "none") << "]\n");
+  LLVM_DEBUG(dbgs() << "addUndefinedFunction: " << Name << " ["
+                    << (Sig ? toString(*Sig) : "none")
+                    << "] IsCalledDirectly:" << IsCalledDirectly << "\n");
 
   Symbol *S;
   bool WasInserted;
   std::tie(S, WasInserted) = insert(Name, File);
   if (S->Traced)
     printTraceSymbolUndefined(Name, File);
 
   auto Replace = [&]() {
     replaceSymbol<UndefinedFunction>(S, Name, ImportName, ImportModule, Flags,
                                      File, Sig, IsCalledDirectly);
   };
 
   if (WasInserted)
     Replace();
   else if (auto *Lazy = dyn_cast<LazySymbol>(S))
     Lazy->fetch();
   else {
     auto ExistingFunction = dyn_cast<FunctionSymbol>(S);
     if (!ExistingFunction) {
       reportTypeError(S, File, WASM_SYMBOL_TYPE_FUNCTION);
       return S;
     }
+    if (!ExistingFunction->Signature && Sig)
+      ExistingFunction->Signature = Sig;
     if (IsCalledDirectly && !signatureMatches(ExistingFunction, Sig))
       if (getFunctionVariant(S, Sig, File, &S))
         Replace();
   }
 
   return S;
 }