[wasm][liftoff][eh] Fix access to empty try info

If the block is unreachable, the interface is not called and the
{try_info} field is not set. Therefore, check it before accessing it.

R=clemensb@chromium.org

Bug: chromium:1188975
Change-Id: Ic6d7d2b7e26b0448143076e25a89c036216e8618
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2767017Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73480}

src/wasm/baseline/liftoff-compiler.cc

@@ -568,7 +568,7 @@ class LiftoffCompiler {
       Control* c = decoder->control_at(i);
       Unuse(c->label.get());
       if (c->else_state) Unuse(c->else_state->label.get());
-      if (c->is_try()) Unuse(&c->try_info->catch_label);
+      if (c->try_info != nullptr) Unuse(&c->try_info->catch_label);
     }
     for (auto& ool : out_of_line_code_) Unuse(ool.label.get());
 #endif

test/mjsunit/regress/wasm/regress-1188975.js

+// Copyright 2021 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --experimental-wasm-eh
+
+load("test/mjsunit/wasm/wasm-module-builder.js");
+
+(function Regress1188975() {
+  print(arguments.callee.name);
+  let builder = new WasmModuleBuilder();
+  builder.addFunction("f", kSig_v_v)
+      .addBody([
+        kExprUnreachable,
+        kExprTry, kWasmStmt,
+        kExprElse,
+        kExprCatchAll,
+        kExprEnd,
+      ]);
+  assertThrows(() => builder.instantiate(), WebAssembly.CompileError);
+})();