[lld][WebAssembly] Fix handling of comdat functions in init array.

When hidden symbols are discarded by comdat rules we still want to
create a local defined symbol, otherwise `Symbol::isDiscarded()` relies
on begin able to check `getChunk->discarded`.

This is a followup on rL362769. The comdat.ll test was previously GC'ing
the `__wasm_call_ctors` functions so `do_init` was not actually being
included in the link.  Once that function was included in triggered the
crash bug that this change addresses.

Fixes: emscripten-core/emscripten#8981

Differential Revision: https://reviews.llvm.org/D64872

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@366358 91177308-0d34-0410-b5e6-96231b3b80d8

test/wasm/Inputs/comdat1.ll

@@ -12,8 +12,8 @@ define internal void @do_init() comdat($foo) {
   ret void
 }
 
-@llvm.global_ctors = appending global [1 x { i32, void ()*, i8* }] [{ i32, void
-()*, i8* } { i32 65535, void ()* @do_init, i8* null }]
+%0 = type { i32, void ()*, i8* }
+@llvm.global_ctors = appending global [1 x %0 ] [%0 { i32 65535, void ()* @do_init, i8* null }]
 
 ; Everything above this is part of the `foo` comdat group
 

test/wasm/Inputs/comdat2.ll

@@ -12,8 +12,8 @@ define internal void @do_init() comdat($foo) {
   ret void
 }
 
-@llvm.global_ctors = appending global [1 x { i32, void ()*, i8* }] [{ i32, void
-()*, i8* } { i32 65535, void ()* @do_init, i8* null }]
+%0 = type { i32, void ()*, i8* }
+@llvm.global_ctors = appending global [1 x %0] [ %0 { i32 65535, void ()* @do_init, i8* getelementptr inbounds ([3 x i8], [3 x i8]* @constantData, i32 0, i32 0) }]
 
 ; Everything above this is part of the `foo` comdat group
 

test/wasm/comdats.ll

@@ -6,10 +6,12 @@
 
 target triple = "wasm32-unknown-unknown"
 
+declare void @__wasm_call_ctors()
 declare i32 @comdatFn()
 
 define void @_start() {
 entry:
+  call void @__wasm_call_ctors()
   %call = call i32 @comdatFn()
   ret void
 }
@@ -35,38 +37,44 @@ entry:
 ; CHECK-NEXT:        Index:           0
 ; CHECK-NEXT:      - Name:            _start
 ; CHECK-NEXT:        Kind:            FUNCTION
-; CHECK-NEXT:        Index:           0
+; CHECK-NEXT:        Index:           1
 ; CHECK-NEXT:      - Name:            comdatFn
 ; CHECK-NEXT:        Kind:            FUNCTION
-; CHECK-NEXT:        Index:           1
+; CHECK-NEXT:        Index:           2
 ; CHECK-NEXT:      - Name:            constantData
 ; CHECK-NEXT:        Kind:            GLOBAL
 ; CHECK-NEXT:        Index:           1
 ; CHECK-NEXT:      - Name:            callComdatFn1
 ; CHECK-NEXT:        Kind:            FUNCTION
-; CHECK-NEXT:        Index:           2
+; CHECK-NEXT:        Index:           4
 ; CHECK-NEXT:      - Name:            callComdatFn2
 ; CHECK-NEXT:        Kind:            FUNCTION
-; CHECK-NEXT:        Index:           3
+; CHECK-NEXT:        Index:           5
 ; CHECK-NEXT:  - Type:            ELEM
 ; CHECK-NEXT:    Segments:
 ; CHECK-NEXT:      - Offset:
 ; CHECK-NEXT:          Opcode:          I32_CONST
 ; CHECK-NEXT:          Value:           1
-; CHECK-NEXT:        Functions:       [ 1 ]
+; CHECK-NEXT:        Functions:       [ 2 ]
 ; CHECK-NEXT:  - Type:            CODE
 ; CHECK-NEXT:    Functions:
 ; CHECK-NEXT:      - Index:           0
 ; CHECK-NEXT:        Locals:
-; CHECK-NEXT:        Body:            1081808080001A0B
+; CHECK-NEXT:        Body:            10030B
 ; CHECK-NEXT:      - Index:           1
 ; CHECK-NEXT:        Locals:
-; CHECK-NEXT:        Body:            4180888080000B
+; CHECK-NEXT:        Body:            1080808080001082808080001A0B
 ; CHECK-NEXT:      - Index:           2
 ; CHECK-NEXT:        Locals:
-; CHECK-NEXT:        Body:            4181808080000B
+; CHECK-NEXT:        Body:            4180888080000B
 ; CHECK-NEXT:      - Index:           3
 ; CHECK-NEXT:        Locals:
+; CHECK-NEXT:        Body:            0B
+; CHECK-NEXT:      - Index:           4
+; CHECK-NEXT:        Locals:
+; CHECK-NEXT:        Body:            4181808080000B
+; CHECK-NEXT:      - Index:           5
+; CHECK-NEXT:        Locals:
 ; CHECK-NEXT:        Body:            4181808080000B
 ; CHECK-NEXT:  - Type:            DATA
 ; CHECK-NEXT:    Segments:

wasm/InputFiles.cpp

@@ -380,22 +380,20 @@ Symbol *ObjFile::createDefined(const WasmSymbol &sym) {
   case WASM_SYMBOL_TYPE_FUNCTION: {
     InputFunction *func =
         functions[sym.Info.ElementIndex - wasmObj->getNumImportedFunctions()];
-    if (func->discarded)
-      return nullptr;
     if (sym.isBindingLocal())
       return make<DefinedFunction>(name, flags, this, func);
+    if (func->discarded)
+      return nullptr;
     return symtab->addDefinedFunction(name, flags, this, func);
   }
   case WASM_SYMBOL_TYPE_DATA: {
     InputSegment *seg = segments[sym.Info.DataRef.Segment];
-    if (seg->discarded)
-      return nullptr;
-
     uint32_t offset = sym.Info.DataRef.Offset;
     uint32_t size = sym.Info.DataRef.Size;
-
     if (sym.isBindingLocal())
       return make<DefinedData>(name, flags, this, seg, offset, size);
+    if (seg->discarded)
+      return nullptr;
     return symtab->addDefinedData(name, flags, this, seg, offset, size);
   }
   case WASM_SYMBOL_TYPE_GLOBAL: {

wasm/Writer.cpp

@@ -821,6 +821,7 @@ void Writer::calculateInitFunctions() {
       assert(sym->isLive());
       if (*sym->signature != WasmSignature{{}, {}})
         error("invalid signature for init func: " + toString(*sym));
+      LLVM_DEBUG(dbgs() << "initFunctions: " << toString(*sym) << "\n");
       initFunctions.emplace_back(WasmInitEntry{sym, f.Priority});
     }
   }