[PATCH][RFC] Instrument function exit with __builtin_unreachable in C++.

[Martin Liška]

On 10/24/2017 04:19 PM, Jason Merrill wrote:
> On 10/18/2017 09:07 AM, Martin Liška wrote:
>> @@ -1182,7 +1182,13 @@ cxx_eval_builtin_function_call (const constexpr_ctx *ctx, tree t, tree fun,
>> Â Â Â Â  {
>> Â Â Â Â Â Â  new_call = build_call_array_loc (EXPR_LOCATION (t), TREE_TYPE (t),
>> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â  CALL_EXPR_FN (t), nargs, args);
>> -Â Â Â Â Â  error ("%q+E is not a constant expression", new_call);
>> +
>> +      /* Do not allow__builtin_unreachable in constexpr function.  */
>> +Â Â Â Â Â  if (DECL_FUNCTION_CODE (fun) == BUILT_IN_UNREACHABLE
>> +Â Â Â Â Â Â Â Â Â  && EXPR_LOCATION (t) == BUILTINS_LOCATION)
>> +Â Â Â Â Â Â Â  error ("constexpr call flows off the end of the function");
>> +Â Â Â Â Â  else
>> +Â Â Â Â Â Â Â  error ("%q+E is not a constant expression", new_call);
> 
> You don't need to build new_call in the new case, since you don't use it.
> 
> Also, please adjust the comment to say that a __builtin_unreachable call with BUILTINS_LOCATION comes from cp_maybe_instrument_return.
> 
> OK with those changes.
> 
> Jason

Hi.

Thank you for review, done that.
Can you please take a look at the single problematic test-case that blocks acceptance of the patch to trunk?

Martin
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