[WebAssembly] Handle aliases in WebAssemblyFixFunctionBitcasts

[sbc100]

Summary

Fixes: https://github.com/emscripten-core/emscripten/issues/8770

llvm/lib/Target/WebAssembly/WebAssemblyFixFunctionBitcasts.cpp

 // Recursively descend the def-use lists from V to find non-bitcast users of
 // bitcasts of V.
 static void findUses(Value *V, Function &F,
                      SmallVectorImpl<std::pair<Use *, Function *>> &Uses,
                      SmallPtrSetImpl<Constant *> &ConstantBCs) {
   for (Use &U : V->uses()) {
     if (auto *BC = dyn_cast<BitCastOperator>(U.getUser()))
       findUses(BC, F, Uses, ConstantBCs);
+    else if (auto *A = dyn_cast<GlobalAlias>(U.getUser()))
+      findUses(A, F, Uses, ConstantBCs);
     else if (U.get()->getType() != F.getType()) {
       CallSite CS(U.getUser());
       if (!CS)
         // Skip uses that aren't immediately called
         continue;
       Value *Callee = CS.getCalledValue();
       if (Callee != V)
         // Skip calls where the function isn't the callee

llvm/test/CodeGen/WebAssembly/function-bitcasts.ll

 ; RUN: llc < %s -asm-verbose=false -wasm-disable-explicit-locals -wasm-keep-registers -enable-emscripten-cxx-exceptions | FileCheck %s
 
 ; Test that function pointer casts are replaced with wrappers.
 
 target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
 target triple = "wasm32-unknown-unknown"
 
-declare void @has_i32_arg(i32)
+define void @has_i32_arg(i32) {
+entry:
+  ret void
+}
+
 declare void @has_struct_arg({i32})
 declare i32 @has_i32_ret()
 declare void @vararg(...)
 declare void @plain(i32)
 
 declare void @foo0()
 declare void @foo1()
 declare void @foo2()
entry:
   %t = call i32 bitcast (void ()* @foo1 to i32 ()*)()
   call void bitcast (void ()* @foo2 to void ()*)()
   call void @foo1()
   call void @foo3()
 
   ret void
 }
 
+; Calling aliases should also generate a wrapper
+
+@alias_i32_arg = weak hidden alias void (i32), void (i32)* @has_i32_arg
+
+; CHECK-LABEL: test_alias:
+; CHECK: call    .Lhas_i32_arg_bitcast.2
+define void @test_alias() {
+entry:
+  call void bitcast (void (i32)* @alias_i32_arg to void ()*)()
+  ret void
+}
+
+
 ; CHECK-LABEL: test_structs:
 ; CHECK: call     .Lhas_i32_arg_bitcast.1, $pop{{[0-9]+}}, $pop{{[0-9]+$}}
 ; CHECK: call     .Lhas_i32_arg_bitcast, $0, $pop2
 ; CHECK: call     .Lhas_struct_arg_bitcast{{$}}
 define void @test_structs() {
 entry:
   call void bitcast (void (i32)* @has_i32_arg to void (i32, {i32})*)(i32 5, {i32} {i32 6})
   call {i32, i64} bitcast (void (i32)* @has_i32_arg to {i32, i64} (i32)*)(i32 7)