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Re: PR83648
- From: Richard Biener <rguenther at suse dot de>
- To: Prathamesh Kulkarni <prathamesh dot kulkarni at linaro dot org>,gcc Patches <gcc-patches at gcc dot gnu dot org>,Jan Hubicka <hubicka at ucw dot cz>
- Date: Wed, 03 Jan 2018 10:05:30 +0100
- Subject: Re: PR83648
- Authentication-results: sourceware.org; auth=none
- References: <CAAgBjMnap+eF165TdbZrpAmU2=stko03z0OOzsHwd_Bca+MN9g@mail.gmail.com>
On January 3, 2018 7:03:26 AM GMT+01:00, Prathamesh Kulkarni <prathamesh.kulkarni@linaro.org> wrote:
>Hi,
>malloc_candidate_p() in ipa-pure-const misses detecting that a
>function is malloc-like if the return value is result of PHI and one
>of the arguments of PHI is 0.
>For example:
>
>void g(unsigned n)
>{
> return (n) ? __builtin_malloc (n) : 0;
>}
>
>The reason is that the following check:
>if (TREE_CODE (arg) != SSA_NAME)
> DUMP_AND_RETURN ("phi arg is not SSA_NAME.")
>
>fails for arg with constant value 0 and malloc_candidate_p returns
>false.
>The patch simply skips the arg if it equals null_pointer_node.
>Does it look OK ?
Please use integer_zerop instead of a literal compare. I'm not sure how to handle targets where address zero is valid (flag_no_delete_null_pointer_chekcs)
>One concern I have is that with the patch, malloc_candidate_p will
>return true if all the args to PHI are NULL:
>retval = PHI<0, 0>
>return retval
>
>However I expect that PHI with all 0 args would be constant folded to
>0 earlier, so this case shouldn't occur in practice ?
You may not rely on folding for correctness.
>Bootstrapped+tested on x86_64-unknown-linux-gnu.
>Cross-testing on arm*-*-* and aarch64*-*-* in progress.
>
>Thanks,
>Prathamesh