[WebAssembly] Fix MCNullStreamer support

[eush]

Summary

This fixes crashes in AsmPrinter when using MCNullStreamer
(-filetype=null).

With MCNullStreamer, getTargetStreamer returns null, so this
patch adds some null checks to avoid a crash.

[sbc100]

test/CodeGen/WebAssembly/null-streamer.ll

11

Can you simplify this test, drop the trow and remove the exception arguments from llc?

[eush]

test/CodeGen/WebAssembly/null-streamer.ll

11

Can I wonder why? A simpler test would only exercise changes in EmitFunctionBodyStart and wouldn't need any changes in EmitEndOfAsmFile.

[sbc100]

test/CodeGen/WebAssembly/null-streamer.ll

11

Oh I see. I just found a it a little strange to have those options enabled, but I suppose it makes sense. Alternatively you could call alloca in order to trigger the use of __stack_pointer.

Also, if you want to be sure you excersise those parts maybe you would want to at a CHECK: for the .globaltype and/or .eventtype at the end?

[aheejin]

Thanks for doing this! By the way, every time we use getTargetStreamer(), are we required do this? I checked some other *AsmPrinter.cpp files for other targets and it seems they are not doing this, but they can run -filetype=null with no problem. I wonder what makes the difference?

test/CodeGen/WebAssembly/null-streamer.ll

11

This is nullstreamer, so I guess it wouldn't print anything so we can't check.

[aheejin]

I opened D54660. I think this way we don't need to use if (WebAssemblyTargetStreamer *TS = getTargetStreamer()) ... every time we use getTargetStreamer(). What do you think?

[eush]

In D54614#1301891, @aheejin wrote:

I opened D54660. I think this way we don't need to use if (WebAssemblyTargetStreamer *TS = getTargetStreamer()) ... every time we use getTargetStreamer(). What do you think?

I think that's great! I didn't know about RegisterNullTargetStreamer - it looks to me like the correct way to support MCNullStreamer.

test/CodeGen/WebAssembly/null-streamer.ll

11

This is nullstreamer, so I guess it wouldn't print anything so we can't check.

That is unless we add a second RUN line with a default streamer, just for the checks.

[aheejin]

test/CodeGen/WebAssembly/null-streamer.ll

11

This might be a better idea, having a second RUN line. I'll fix that in D54660,

[eush]

Abandoned in favor of D54660.

lib/Target/WebAssembly/WebAssemblyAsmPrinter.cpp

 //===----------------------------------------------------------------------===//
 // WebAssemblyAsmPrinter Implementation.
 //===----------------------------------------------------------------------===//
 
 void WebAssemblyAsmPrinter::EmitEndOfAsmFile(Module &M) {
   for (auto &It : OutContext.getSymbols()) {
     // Emit a .globaltype and .eventtype declaration.
     auto Sym = cast<MCSymbolWasm>(It.getValue());
+    if (WebAssemblyTargetStreamer *TS = getTargetStreamer()) {
       if (Sym->getType() == wasm::WASM_SYMBOL_TYPE_GLOBAL)
-      getTargetStreamer()->emitGlobalType(Sym);
+        TS->emitGlobalType(Sym);
       else if (Sym->getType() == wasm::WASM_SYMBOL_TYPE_EVENT)
-      getTargetStreamer()->emitEventType(Sym);
+        TS->emitEventType(Sym);
+    }
   }
 
   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.getFunctionType(), F, TM, Params, Results);
       auto *Sym = cast<MCSymbolWasm>(getSymbol(&F));
       if (!Sym->getSignature()) {
         auto Signature = SignatureFromMVTs(Results, Params);
         Sym->setSignature(Signature.get());
         addSignature(std::move(Signature));
       }
-      // FIXME: this was originally intended for post-linking and was only used
-      // for imports that were only called indirectly (i.e. s2wasm could not
-      // infer the type from a call). With object files it applies to all
-      // imports. so fix the names and the tests, or rethink how import
-      // delcarations work in asm files.
-      getTargetStreamer()->emitIndirectFunctionType(Sym);
+      if (WebAssemblyTargetStreamer *TS = getTargetStreamer()) {
+        // FIXME: this was originally intended for post-linking and was only
+        // used for imports that were only called indirectly (i.e. s2wasm
+        // could not infer the type from a call). With object files it applies
+        // to all imports. so fix the names and the tests, or rethink how
+        // import declarations work in asm files.
+        TS->emitIndirectFunctionType(Sym);
 
         if (TM.getTargetTriple().isOSBinFormatWasm() &&
             F.hasFnAttribute("wasm-import-module")) {
           StringRef Name =
               F.getFnAttribute("wasm-import-module").getValueAsString();
-        getTargetStreamer()->emitImportModule(Sym, Name);
+          TS->emitImportModule(Sym, Name);
+        }
       }
     }
   }
 
   for (const auto &G : M.globals()) {
     if (!G.hasInitializer() && G.hasExternalLinkage()) {
       if (G.getValueType()->isSized()) {
         uint16_t Size = M.getDataLayout().getTypeAllocSize(G.getValueType());
void WebAssemblyAsmPrinter::EmitFunctionBodyStart() {
   SmallVector<MVT, 1> ResultVTs;
   SmallVector<MVT, 4> ParamVTs;
   ComputeSignatureVTs(F.getFunctionType(), F, TM, ParamVTs, ResultVTs);
   auto Signature = SignatureFromMVTs(ResultVTs, ParamVTs);
   auto *WasmSym = cast<MCSymbolWasm>(CurrentFnSym);
   WasmSym->setSignature(Signature.get());
   addSignature(std::move(Signature));
 
+  if (WebAssemblyTargetStreamer *TS = getTargetStreamer()) {
     // FIXME: clean up how params and results are emitted (use signatures)
-  getTargetStreamer()->emitParam(CurrentFnSym, ParamVTs);
+    TS->emitParam(CurrentFnSym, ParamVTs);
 
     // Emit the function index.
     if (MDNode *Idx = F.getMetadata("wasm.index")) {
       assert(Idx->getNumOperands() == 1);
 
-    getTargetStreamer()->emitIndIdx(AsmPrinter::lowerConstant(
+      TS->emitIndIdx(AsmPrinter::lowerConstant(
           cast<ConstantAsMetadata>(Idx->getOperand(0))->getValue()));
     }
 
-  getTargetStreamer()->emitResult(CurrentFnSym, ResultVTs);
-  getTargetStreamer()->emitLocal(MFI->getLocals());
+    TS->emitResult(CurrentFnSym, ResultVTs);
+    TS->emitLocal(MFI->getLocals());
+  }
 
   AsmPrinter::EmitFunctionBodyStart();
 }
 
 void WebAssemblyAsmPrinter::EmitInstruction(const MachineInstr *MI) {
   LLVM_DEBUG(dbgs() << "EmitInstruction: " << *MI << '\n');
 
   switch (MI->getOpcode()) {

test/CodeGen/WebAssembly/null-streamer.ll

+; RUN: llc -O0 -filetype=null -exception-model=wasm -mattr=+exception-handling < %s
+
+target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
+target triple = "wasm32-unknown-unknown"
+
+declare void @llvm.wasm.throw(i32, i8*)
+
+declare void @g()
+
+define i32 @f(i8* %p)  {
+  call void @llvm.wasm.throw(i32 0, i8* %p)
+  call void @g()
+  ret i32 0
+}