[lld][WebAssembly] Allow globals imports via import_name/import_module

[sbc100]

Summary

This feature already exists but was limited to function
symbols.

[tlively]

Should F and G be lowercased? It looks like the surrounding code uses camelCase fairly uniformly.

[sbc100]

In D87666#2272988, @tlively wrote:

Should F and G be lowercased? It looks like the surrounding code uses camelCase fairly uniformly.

Yup. old habbits

[sbc100]

feedback

lld/test/wasm/mutable-globals.s

 # RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown -o %t.o %s
 # RUN: not wasm-ld %t.o -o %t.wasm 2>&1 | FileCheck %s
 
 .globl _start
 _start:
   .functype _start () -> ()
   i32.const 1
   global.set foo
   end_function
 
 .globaltype foo, i32
+.import_module foo, env
+.import_name foo, foo
 
 # CHECK: error: mutable global imported but 'mutable-globals' feature not present in inputs: `foo`. Use --no-check-features to suppress.

lld/wasm/Relocations.cpp

 
 namespace lld {
 namespace wasm {
 static bool requiresGOTAccess(const Symbol *sym) {
   return config->isPic && !sym->isHidden() && !sym->isLocal();
 }
 
 static bool allowUndefined(const Symbol* sym) {
-  // Undefined functions with explicit import name are allowed to be undefined
-  // at link time.
+  // Undefined functions and globals with explicit import name are allowed to be
+  // undefined at link time.
   if (auto *F = dyn_cast<UndefinedFunction>(sym))
     if (F->importName)
       return true;
+  if (auto *G = dyn_cast<UndefinedGlobal>(sym))
+    if (G->importName)
+      return true;
   return (config->allowUndefined ||
           config->allowUndefinedSymbols.count(sym->getName()) != 0);
 }
 
 static void reportUndefined(const Symbol* sym) {
   assert(sym->isUndefined());
   assert(!sym->isWeak());
   if (!allowUndefined(sym))