[wasm] Let BranchTableIterator::has_next return false if decoder->failed()

src/wasm/ast-decoder.h

 // Copyright 2015 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.
 
 #ifndef V8_WASM_AST_DECODER_H_
 #define V8_WASM_AST_DECODER_H_
 
 #include "src/signature.h"
 #include "src/wasm/decoder.h"
 #include "src/wasm/wasm-opcodes.h"
@@ skipping 216 matching lines @@
   inline uint32_t read_entry(Decoder* decoder, unsigned i) {
     DCHECK(i <= table_count);
     return table ? decoder->read_u32(table + i * sizeof(uint32_t)) : 0;
   }
 };
 
 // A helper to iterate over a branch table.
 class BranchTableIterator {
  public:
   unsigned cur_index() { return index_; }
-  bool has_next() { return index_ <= table_count_; }
+  bool has_next() { return decoder_->ok() && index_ <= table_count_; }

[titzer, 2016/10/13 13:46:10]

Does this obviate the previous fix?

[ahaas, 2016/10/13 13:53:44]

This change does not prevent any crashes, it just reduces the time it takes to
decode an invalid function.

   uint32_t next() {
     DCHECK(has_next());
     index_++;
     unsigned length = 0;
     uint32_t result =
         decoder_->checked_read_u32v(pc_, 0, &length, "branch table entry");
     pc_ += length;
     return result;
   }
   // length, including the length of the {BranchTableOperand}, but not the
@@ skipping 165 matching lines @@
   }
 
   bool has_next() { return pc_ < end_; }
 };
 
 }  // namespace wasm
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_WASM_AST_DECODER_H_