[WebAssembly] Handle weak undefined functions with a synthetic stub

This error case is described in Linking.md. The operand for call requires
generation of a synthetic stub.

Differential Revision: https://reviews.llvm.org/D44028

llvm-svn: 327151
diff --git a/lld/wasm/InputFiles.cpp b/lld/wasm/InputFiles.cpp
index 2c65c7b..12ee9ec 100644
--- a/lld/wasm/InputFiles.cpp
+++ b/lld/wasm/InputFiles.cpp
@@ -65,14 +65,8 @@
 uint32_t ObjFile::calcNewValue(const WasmRelocation &Reloc) const {
   switch (Reloc.Type) {
   case R_WEBASSEMBLY_TABLE_INDEX_I32:
-  case R_WEBASSEMBLY_TABLE_INDEX_SLEB: {
-    // The null case is possible, if you take the address of a weak function
-    // that's simply not supplied.
-    FunctionSymbol *Sym = getFunctionSymbol(Reloc.Index);
-    if (Sym->hasTableIndex())
-      return Sym->getTableIndex();
-    return 0;
-  }
+  case R_WEBASSEMBLY_TABLE_INDEX_SLEB:
+    return getFunctionSymbol(Reloc.Index)->getTableIndex();
   case R_WEBASSEMBLY_MEMORY_ADDR_SLEB:
   case R_WEBASSEMBLY_MEMORY_ADDR_I32:
   case R_WEBASSEMBLY_MEMORY_ADDR_LEB: