[wasm] [cleanup] Mark {UnsupportedOpcode} as noreturn

This allows us to just call this method without returning dummy
{nullptr} values or even calling {graph()->NewNode()} afterwards.

R=ahaas@chromium.org
BUG=v8:6474

Change-Id: I6c03eb639dfb635ce791e7d3a731d9dfdf7800a8
Reviewed-on: https://chromium-review.googlesource.com/529308
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45840}

src/compiler/wasm-compiler.cc

@@ -45,16 +45,15 @@
 #define WASM_64 0
 #endif
 
+#define FATAL_UNSUPPORTED_OPCODE(opcode)                              \
+  V8_Fatal(__FILE__, __LINE__, "Unsupported opcode #%d:%s", (opcode), \
+           wasm::WasmOpcodes::OpcodeName(opcode));
+
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 namespace {
-const Operator* UnsupportedOpcode(wasm::WasmOpcode opcode) {
-  V8_Fatal(__FILE__, __LINE__, "Unsupported opcode #%d:%s", opcode,
-           wasm::WasmOpcodes::OpcodeName(opcode));
-  return nullptr;
-}
 
 void MergeControlToEnd(JSGraph* jsgraph, Node* node) {
   Graph* g = jsgraph->graph();
@@ -585,7 +584,7 @@ Node* WasmGraphBuilder::Binop(wasm::WasmOpcode opcode, Node* left, Node* right,
     case wasm::kExprF64AsmjsStoreMem:
       return BuildAsmjsStoreMem(MachineType::Float64(), left, right);
     default:
-      op = UnsupportedOpcode(opcode);
+      FATAL_UNSUPPORTED_OPCODE(opcode);
   }
   return graph()->NewNode(op, left, right);
 }
@@ -846,7 +845,7 @@ Node* WasmGraphBuilder::Unop(wasm::WasmOpcode opcode, Node* input,
     case wasm::kExprF64AsmjsLoadMem:
       return BuildAsmjsLoadMem(MachineType::Float64(), input);
     default:
-      op = UnsupportedOpcode(opcode);
+      FATAL_UNSUPPORTED_OPCODE(opcode);
   }
   return graph()->NewNode(op, input);
 }
@@ -3502,7 +3501,7 @@ Node* WasmGraphBuilder::SimdOp(wasm::WasmOpcode opcode,
     case wasm::kExprS1x16AllTrue:
       return graph()->NewNode(jsgraph()->machine()->S1x16AllTrue(), inputs[0]);
     default:
-      return graph()->NewNode(UnsupportedOpcode(opcode));
+      FATAL_UNSUPPORTED_OPCODE(opcode);
   }
 }
 
@@ -3535,7 +3534,7 @@ Node* WasmGraphBuilder::SimdLaneOp(wasm::WasmOpcode opcode, uint8_t lane,
       return graph()->NewNode(jsgraph()->machine()->I8x16ReplaceLane(lane),
                               inputs[0], inputs[1]);
     default:
-      return graph()->NewNode(UnsupportedOpcode(opcode));
+      FATAL_UNSUPPORTED_OPCODE(opcode);
   }
 }
 
@@ -3568,7 +3567,7 @@ Node* WasmGraphBuilder::SimdShiftOp(wasm::WasmOpcode opcode, uint8_t shift,
       return graph()->NewNode(jsgraph()->machine()->I8x16ShrU(shift),
                               inputs[0]);
     default:
-      return graph()->NewNode(UnsupportedOpcode(opcode));
+      FATAL_UNSUPPORTED_OPCODE(opcode);
   }
 }