[lld][WebAssembly] Fix malformed output with -pie + --shared-memory

[sbc100]

Summary

The conditional guarding createInitMemoryFunction was incorrect and
didn't match that guarding the creation of the associated symbol.

Rather that reproduce the same conditions in multiple places we can
simply use the presence of the associated symbol.

Also, add an assertion that would have caught this bug.

Also, add a new test for this flag combination.

[sbc100]

• remove some debugging

lld/test/wasm/data-segments.ll

 ; RUN: llc -filetype=obj %s -o %t.atomics.o -mattr=+atomics
 ; RUN: llc -filetype=obj %s -o %t.bulk-mem.o -mattr=+bulk-memory
 ; RUN: llc -filetype=obj %s -o %t.atomics.bulk-mem.o -mattr=+atomics,+bulk-memory
 
 ; atomics, shared memory => error
 ; RUN: not wasm-ld -no-gc-sections --no-entry --shared-memory --max-memory=131072 %t.atomics.o -o %t.atomics.wasm 2>&1 | FileCheck %s --check-prefix ERROR
 
 ; bulk memory, unshared memory => active segments
 ; RUN: wasm-ld -no-gc-sections --no-entry %t.bulk-mem.o -o %t.bulk-mem.wasm
 ; RUN: obj2yaml %t.bulk-mem.wasm | FileCheck %s --check-prefix ACTIVE
 
 ; atomics, bulk memory, shared memory => passive segments
 ; RUN: wasm-ld -no-gc-sections --no-entry --shared-memory --max-memory=131072 %t.atomics.bulk-mem.o -o %t.atomics.bulk-mem.wasm
 ; RUN: obj2yaml %t.atomics.bulk-mem.wasm | FileCheck %s --check-prefixes PASSIVE
 
+; Also test in combination with PIC/pie
+; RUN: llc -filetype=obj -relocation-model=pic %s -o %t.atomics.bulk-mem.pic.o -mattr=+atomics,+bulk-memory,+mutable-globals
+; RUN: wasm-ld --experimental-pic -pie -no-gc-sections --no-entry --shared-memory --max-memory=131072 %t.atomics.bulk-mem.pic.o -o %t.pic.wasm
+
 target triple = "wasm32-unknown-unknown"
 
 @a = hidden global [6 x i8] c"hello\00", align 1
 @b = hidden global [8 x i8] c"goodbye\00", align 1
 @c = hidden global [10000 x i8] zeroinitializer, align 1
 @d = hidden global i32 42, align 4
 
 @e = private constant [9 x i8] c"constant\00", align 1

lld/wasm/MarkLive.cpp

void MarkLive::run() {
   if (!config->entry.empty())
     enqueue(symtab->find(config->entry));
 
   // We need to preserve any no-strip or exported symbol
   for (Symbol *sym : symtab->getSymbols())
     if (sym->isNoStrip() || sym->isExported())
       enqueue(sym);
 
-  // If we'll be calling the user's `__wasm_call_dtors` function, mark it live.
-  if (Symbol *callDtors = WasmSym::callDtors)
-    enqueue(callDtors);
+  if (WasmSym::callDtors)
+    enqueue(WasmSym::callDtors);
 
-  // In Emscripten-style PIC, `__wasm_call_ctors` calls `__wasm_apply_relocs`.
-  if (config->isPic)
+  if (WasmSym::applyRelocs)
     enqueue(WasmSym::applyRelocs);
 
-  if (config->sharedMemory && !config->shared)
+  if (WasmSym::initMemory)
     enqueue(WasmSym::initMemory);
 
   // Enqueue constructors in objects explicitly live from the command-line.
   for (const ObjFile *obj : symtab->objectFiles)
     if (obj->isLive())
       enqueueInitFunctions(obj);
 
   mark();

lld/wasm/OutputSections.cpp

void CodeSection::finalizeContents() {
   writeUleb128(os, functions.size(), "function count");
   os.flush();
   bodySize = codeSectionHeader.size();
 
   for (InputFunction *func : functions) {
     func->outputSec = this;
     func->outputOffset = bodySize;
     func->calculateSize();
+    // All functions should have a non-empty body at this point
+    assert(func->getSize());
     bodySize += func->getSize();
   }
 
   createHeader(bodySize);
 }
 
 void CodeSection::writeTo(uint8_t *buf) {
   log("writing " + toString(*this));

lld/wasm/Writer.cpp

void Writer::run() {
   log("-- scanRelocations");
   scanRelocations();
   log("-- assignIndexes");
   assignIndexes();
   log("-- calculateInitFunctions");
   calculateInitFunctions();
 
   if (!config->relocatable) {
-    // Create linker synthesized functions
-    if (config->isPic)
+    if (WasmSym::applyRelocs)
       createApplyRelocationsFunction();
-    else if (config->sharedMemory)
+    if (WasmSym::initMemory)
       createInitMemoryFunction();
+
+    // Create linker synthesized functions
     createCallCtorsFunction();
 
     // Create export wrappers for commands if needed.
     //
     // If the input contains a call to `__wasm_call_ctors`, either in one of
     // the input objects or an explicit export from the command-line, we
     // assume ctors and dtors are taken care of already.
     if (!config->relocatable && !config->isPic &&