[WebAssembly][MC] Allow empty assembly functions

[aardappel]

llvm/test/MC/WebAssembly/basic-assembly.s

6

add corresponding # CHECK lines below?

[sbc100]

• feedback

[dschuff]

llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp

762

of -> or?

llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp

if (Name == "block") {
         return true;
     } else if (Name == "end_loop") {
       if (pop(Name, Loop))
         return true;
     } else if (Name == "end_block") {
       if (pop(Name, Block))
         return true;
     } else if (Name == "end_function") {
+      ensureLocals(getStreamer());
       CurrentState = EndFunction;
       if (pop(Name, Function) || ensureEmptyNestingStack())
         return true;
     } else if (Name == "call_indirect" || Name == "return_call_indirect") {
       // This has a special TYPEINDEX operand which in text we
       // represent as a signature, such that we can re-build this signature,
       // attach it to an anonymous symbol, which is what WasmObjectWriter
       // expects to be able to recreate the actual unique-ified type indices.
if (DirectiveID.getString() == ".asciz") {
         return error("Cannot parse string constant: ", Lexer.getTok());
       Out.EmitBytes(StringRef(S.c_str(), S.length() + 1));
       return expect(AsmToken::EndOfStatement, "EOL");
     }
 
     return true; // We didn't process this directive.
   }
 
+  // Called either when the first instruction is parsed of the function ends.
+  void ensureLocals(MCStreamer &Out) {
+    if (CurrentState == FunctionStart) {
+      // We haven't seen a .local directive yet. The streamer requires locals to
+      // be encoded as a prelude to the instructions, so emit an empty list of
+      // locals here.
+      auto &TOut = reinterpret_cast<WebAssemblyTargetStreamer &>(
+          *Out.getTargetStreamer());
+      TOut.emitLocal(SmallVector<wasm::ValType, 0>());
+      CurrentState = FunctionLocals;
+    }
+  }
+
   bool MatchAndEmitInstruction(SMLoc IDLoc, unsigned & /*Opcode*/,
                                OperandVector &Operands, MCStreamer &Out,
                                uint64_t &ErrorInfo,
                                bool MatchingInlineAsm) override {
     MCInst Inst;
     Inst.setLoc(IDLoc);
     unsigned MatchResult =
         MatchInstructionImpl(Operands, Inst, ErrorInfo, MatchingInlineAsm);
     switch (MatchResult) {
     case Match_Success: {
-      if (CurrentState == FunctionStart) {
-        // This is the first instruction in a function, but we haven't seen
-        // a .local directive yet. The streamer requires locals to be encoded
-        // as a prelude to the instructions, so emit an empty list of locals
-        // here.
-        auto &TOut = reinterpret_cast<WebAssemblyTargetStreamer &>(
-            *Out.getTargetStreamer());
-        TOut.emitLocal(SmallVector<wasm::ValType, 0>());
-      }
+      ensureLocals(Out);
       // Fix unknown p2align operands.
       auto Align = WebAssembly::GetDefaultP2AlignAny(Inst.getOpcode());
       if (Align != -1U) {
         auto &Op0 = Inst.getOperand(0);
         if (Op0.getImm() == -1)
           Op0.setImm(Align);
       }
       Out.EmitInstruction(Inst, getSTI());

llvm/test/MC/WebAssembly/basic-assembly.s

 # RUN: llvm-mc -triple=wasm32-unknown-unknown -mattr=+atomics,+unimplemented-simd128,+nontrapping-fptoint,+exception-handling < %s | FileCheck %s
 # Check that it converts to .o without errors, but don't check any output:
 # RUN: llvm-mc -triple=wasm32-unknown-unknown -filetype=obj -mattr=+atomics,+unimplemented-simd128,+nontrapping-fptoint,+exception-handling -o %t.o < %s
 
+
+empty_func:
+    .functype empty_func () -> ()
+    end_function
+
 test0:
     # Test all types:
     .functype   test0 (i32, i64) -> (i32)
     .eventtype  __cpp_exception i32
     .local      f32, f64, v128, v128
     # Explicit getlocal/setlocal:
     local.get   2
     local.set   2
.L.str:
     .section    .init_array.42,"",@
     .p2align    2
     .int32      test0
 
     .ident      "clang version 9.0.0 (trunk 364502) (llvm/trunk 364571)"
     .globaltype __stack_pointer, i32
 
 # CHECK:           .text
+# CHECK-LABEL: empty_func:
+# CHECK-NEXT:      .functype  empty_func () -> ()
+# CHECK-NEXT:      end_function
 # CHECK-LABEL: test0:
 # CHECK-NEXT:      .functype   test0 (i32, i64) -> (i32)
 # CHECK-NEXT:      .eventtype  __cpp_exception i32
 # CHECK-NEXT:      .local      f32, f64
 # CHECK-NEXT:      local.get   2
 # CHECK-NEXT:      local.set   2
 # CHECK-NEXT:      i32.const   -1
 # CHECK-NEXT:      f64.const   0x1.999999999999ap1