[WebAssembly] Fix casting MCSymbol to MCSymbolWasm on ELF

[jgravelle-google]

Summary

wasm32-unknown-unknown-elf has MCSymbols that are not MCSymbolWasms, so
we need a non-asserting cast here.

[dschuff]

lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp

94

Does emitImportModule do anything for ELF? I assume not, maybe it makes more sense to just explicitly condition this whole thing on BinFormatWasm and that way when we remove ELF it will be easy to find all the mentions of BinFormatELF or BinFormatWasm in the backend and remove them.

[jgravelle-google]

• Gate MCSymbolWasm on BinFormatWasm

[jgravelle-google]

lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp

94

Yeah it just asserts if we actually do add a "wasm-import-module" attribute. This is less explicitly unsupported, but more refactorable in future.

[dschuff]

lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp

94

Yeah my hope is that the "future" for ELF is short and does not include this attribute :)

lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp

 
 void WebAssemblyAsmPrinter::EmitEndOfAsmFile(Module &M) {
   for (const auto &F : M) {
     // Emit function type info for all undefined functions
     if (F.isDeclarationForLinker() && !F.isIntrinsic()) {
       SmallVector<MVT, 4> Results;
       SmallVector<MVT, 4> Params;
       ComputeSignatureVTs(F, TM, Params, Results);
-      MCSymbolWasm *Sym = cast<MCSymbolWasm>(getSymbol(&F));
+      MCSymbol *Sym = getSymbol(&F);
       getTargetStreamer()->emitIndirectFunctionType(Sym, Params, Results);
 
-      if (F.hasFnAttribute("wasm-import-module")) {
+      MCSymbolWasm *WasmSym = dyn_cast<MCSymbolWasm>(Sym);
+      if (WasmSym && F.hasFnAttribute("wasm-import-module")) {
         StringRef Name = F.getFnAttribute("wasm-import-module")
                              .getValueAsString();
-        getTargetStreamer()->emitImportModule(Sym, Name);
+        getTargetStreamer()->emitImportModule(WasmSym, Name);
       }
     }
   }
   for (const auto &G : M.globals()) {
     if (!G.hasInitializer() && G.hasExternalLinkage()) {
       if (G.getValueType()->isSized()) {
         uint16_t Size = M.getDataLayout().getTypeAllocSize(G.getValueType());
         if (TM.getTargetTriple().isOSBinFormatELF())