[lld][WebAssembly] Fix for --import-table when combined with reference types

When reference types are enabled clang will generate call_indirect
instructions that explicitly reference the global
`__indirect_function_table` symbol.

In this case the resulting global symbol was not being correctly marked
with explicit import name/module, resulting in the linker reporting
errors when it was referenced.

This issue was reported in WebAssembly/tool-conventions#158

Author: sbc100

lld/test/wasm/import-table-explicit.s

@@ -0,0 +1,26 @@
+# RUN: llvm-mc -mattr=+reference-types -filetype=obj -triple=wasm32-unknown-unknown %s -o %t.o
+# RUN: wasm-ld --import-table -o %t.wasm %t.o
+# RUN: obj2yaml %t.wasm | FileCheck %s
+
+.globl __indirect_function_table
+.tabletype __indirect_function_table, funcref
+
+.globl _start
+_start:
+  .functype _start () -> ()
+  i32.const 1
+  call_indirect __indirect_function_table, () -> ()
+  end_function
+
+# Verify the --import-table flag creates a table import
+
+# CHECK:       - Type:            IMPORT
+# CHECK-NEXT:    Imports:
+# CHECK-NEXT:      - Module:          env
+# CHECK-NEXT:        Field:           __indirect_function_table
+# CHECK-NEXT:        Kind:            TABLE
+# CHECK-NEXT:        Table:
+# CHECK-NEXT:          Index:           0
+# CHECK-NEXT:          ElemType:        FUNCREF
+# CHECK-NEXT:          Limits:
+# CHECK-NEXT:            Minimum:         0x1

lld/test/wasm/import-table.test lld/test/wasm/import-table.s

@@ -1,14 +1,14 @@
-# RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown %p/Inputs/start.s -o %t.start.o
 # RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown %s -o %t.o
-# RUN: wasm-ld --export-all --import-table -o %t.wasm %t.start.o %t.o
+# RUN: wasm-ld --export-all --import-table -o %t.wasm %t.o
 # RUN: obj2yaml %t.wasm | FileCheck %s
 
-.globl require_function_table
-require_function_table:
-.functype require_function_table () -> ()
-          i32.const 1
-          call_indirect () -> ()
-          end_function
+.globl _start
+_start:
+  .functype _start () -> ()
+  i32.const 1
+  # call_indirect instruction implicitly references the function table
+  call_indirect () -> ()
+  end_function
 
 # Verify the --import-table flag creates a table import
 

lld/wasm/SymbolTable.cpp

@@ -681,10 +681,10 @@ TableSymbol *SymbolTable::createUndefinedIndirectFunctionTable(StringRef name) {
   WasmTableType *type = make<WasmTableType>();
   type->ElemType = ValType::FUNCREF;
   type->Limits = limits;
-  StringRef module(defaultModule);
   uint32_t flags = config->exportTable ? 0 : WASM_SYMBOL_VISIBILITY_HIDDEN;
   flags |= WASM_SYMBOL_UNDEFINED;
-  Symbol *sym = addUndefinedTable(name, name, module, flags, nullptr, type);
+  Symbol *sym =
+      addUndefinedTable(name, name, defaultModule, flags, nullptr, type);
   sym->markLive();
   sym->forceExport = config->exportTable;
   return cast<TableSymbol>(sym);
@@ -724,8 +724,11 @@ TableSymbol *SymbolTable::resolveIndirectFunctionTable(bool required) {
   }
 
   if (config->importTable) {
-    if (existing)
+    if (existing) {
+      existing->importModule = defaultModule;
+      existing->importName = functionTableName;
       return cast<TableSymbol>(existing);
+    }
     if (required)
       return createUndefinedIndirectFunctionTable(functionTableName);
   } else if ((existing && existing->isLive()) || config->exportTable ||