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Re: Possible issue with using LAST_INSN_CODE

Hi Jeff,

In the gencodes.c:89, it explicitly  decrements by one the return
value of get_num_insn_codes(). While for the get_num_insn_codes is
stated this:

/* Return the number of possible INSN_CODEs.  Only meaningful once the
   whole file has been processed.  */

I can provide an example for the ARC port where it crashes due to
LAST_INSN_CODE issue. Probably it can be reproduced with other more
popular port like ARM.


On Thu, Aug 20, 2015 at 6:54 PM, Jeff Law <> wrote:
> On 08/20/2015 02:54 AM, Claudiu Zissulescu wrote:
>> Hi,
>> The LAST_INSN_CODE is used to mark the last instruction code valid
>> for a particular architecture (e.g., For ARM the value of
>> LAST_INSN_CODE is 3799). Also this code (i.e., 3799) is used by a
>> predicated instruction (e.g., for ARM this code is used by predicated
>> version of arm_usatsihi => {*p arm_usatsihi}).
>> However, the LAST_INSN_CODE macro is used by lra, recog and
>> tree-vect-stmts to dimension various arrays which may lead to various
>> errors.
>> For example, when calling preprocess_insn_constraints (recog.c:2444),
>> the compilation may go berserk when evaluating  "if
>> (this_target_recog->x_op_alt[icode])" line when icode is  exactly the
>> LAST_INSN_CODE as  "this_target_recog->x_op_alt" is dimensioned up to
>> LAST_INSN_CODE (recog.h:397).
>> A possible solution is having the LAST_INSN_CODE value to be exactly
>> the value returned by get_num_isns_codes() (gencodes.c:89).
>> Alternatively is to use LAST_INSN_CODE+1 when defining an array.
>> Please can someone confirm my observation. And what will be the best
>> solution for this.
> It seems to me like something has been broken then.
> LAST_INSN_CODE is supposed to be higher than any insn defined by the
> backend.
> Jeff

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