[WebAssembly] Fix signature parsing for 'try' in AsmParser

[aheejin]

Summary

Like block or loop, try can take an optional signature which can
be omitted. This patch allows try's signature to be omitted. Also
added some tests for EH instructions.

lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp

while (Lexer.isNot(AsmToken::EndOfStatement)) {
           return true;
       }
     }
     Parser.Lex();
     // Block instructions require a signature index, but these are missing in
     // assembly, so we add a dummy one explicitly (since we have no control
     // over signature tables here, we assume these will be regenerated when
     // the wasm module is generated).
-    if (BaseName == "block" || BaseName == "loop") {
+    if (BaseName == "block" || BaseName == "loop" || BaseName == "try") {
       Operands.push_back(make_unique<WebAssemblyOperand>(
           WebAssemblyOperand::Integer, NameLoc, NameLoc,
           WebAssemblyOperand::IntOp{-1}));
     }
     return false;
   }
 
   void onLabelParsed(MCSymbol *Symbol) override { LastLabel = Symbol; }

test/MC/WebAssembly/basic-assembly.s

-# RUN: llvm-mc -triple=wasm32-unknown-unknown -mattr=+simd128,+nontrapping-fptoint < %s | FileCheck %s
+# RUN: llvm-mc -triple=wasm32-unknown-unknown -mattr=+simd128,+nontrapping-fptoint,+exception-handling < %s | FileCheck %s
 
     .text
     .type    test0,@function
 test0:
     # Test all types:
     .param      i32, i64
     .local      f32, f64, v128, v128
     # Explicit getlocal/setlocal:
.LBB0_2:
     end_block                       # label0:
     get_local   4
     get_local   5
     f32x4.add
     # Test correct parsing of instructions with / and : in them:
     # TODO: enable once instruction has been added.
     #i32x4.trunc_s/f32x4:sat
     i32.trunc_s/f32
+    try
+.LBB0_3:
+    i32.catch   0
+.LBB0_4:
+    catch_all
+.LBB0_5:
+    end_try
     #i32.trunc_s:sat/f32
     get_global  __stack_pointer@GLOBAL
     end_function
 
 
 # CHECK:           .text
 # CHECK-LABEL: test0:
 # CHECK-NEXT:      .param      i32, i64

 # CHECK-NEXT:      br_if 0            # 0: up to label1
 # CHECK-NEXT:  .LBB0_2:
 # CHECK-NEXT:      end_loop
 # CHECK-NEXT:      end_block                       # label0:
 # CHECK-NEXT:      get_local   4
 # CHECK-NEXT:      get_local   5
 # CHECK-NEXT:      f32x4.add
 # CHECK-NEXT:      i32.trunc_s/f32
+# CHECK-NEXT:      try
+# CHECK-NEXT:  .LBB0_3:
+# CHECK-NEXT:      i32.catch   0
+# CHECK-NEXT:  .LBB0_4:
+# CHECK-NEXT:      catch_all
+# CHECK-NEXT:  .LBB0_5:
+# CHECK-NEXT:      end_try
 # CHECK-NEXT:      get_global  __stack_pointer@GLOBAL
 # CHECK-NEXT:      end_function