[PATCH] Add -funknown-commons to work around PR/69368 (and others) in SPEC2006

[Alan Lawrence]

On 25/02/16 18:00, Alan Lawrence wrote:
> On 22/02/16 12:03, Jakub Jelinek wrote:
>> (f) A global command-line option, which we check alongside DECL_COMMON and
>> further tests (basically, we want only DECL_COMMON decls that either have
>> ARRAY_TYPE, or some other aggregate type with flexible array member or some
>> other trailing array in the struct), and use the resulting predicate in
>> places where we optimize based on DECL_SIZE{,_UNIT} of the decl - if that
>> predicate returns true, we assume the DECL_SIZE is
>> "variable"/"unlimited"/whatever.
>> The two spots known to me that would need to use this new predicate would
>> be:
>> tree.c (array_at_struct_end_p):
> [...]
>> tree-dfa.c (get_ref_base_and_extent):
> [...]
>
> Close enough to what I meant by (a)/(b), but never mind that, and I hadn't
> looked at where the change for aggressive loop opts needed to be. However...
> Well you are essentially writing the patch for me at this point (so, thanks!),
>   but here's a patch that puts that under a global -funknown-commons flag.
> Testcase as before.
>
> Bootstrapped (with flag overridden to true) on x86_64 and aarch64, check-gcc,
> check-fortran, and tested 416.gamess on AArch64, where this patch enables
> running *without* the -fno-aggressive-loop-opts previously required.
>
> In the gcc testsuite, these fail with the option turned on:
> gcc.dg/pr53265.c  (test for warnings, line 137)
> gcc.dg/pr53265.c  (test for warnings, line 138)
> gcc.dg/pr64277.c scan-tree-dump cunroll ... (*2)
> gcc.dg/tree-ssa/cunroll-{1,2,3,4,9,10,11}.c scan-tree-dump cunroll/cunrolli/ivcanon (various)
> gcc.dg/tree-ssa/loop-38.c scan-tree-dump cunrolli "Loop 1 iterates at most 11 times"
> ...which all appear harmless.
>
> Thomas Koenig suggests (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69368#c80)
> that this be combined with some flag fiddling and warnings in the Fortran
> front-end; this patch doesn't do that, as I'm not very familiar with the
> frontends, but that can follow in a separate patch. (Thomas?)
>
> OK for trunk?
>
> Cheers, Alan
>
> gcc/ChangeLog:
>
> DATE  Alan Lawrence  <alan.lawrence@arm.com>
>        Jakub Jelinek  <jakub@redhat.com>
>
> 	* common.opt (funknown-commons, flag_unknown_commons): New.
> 	* tree.c (array_at_struct_end_p): Do not limit to size of decl for
> 	DECL_COMMONS if flag_unknown_commons is set.
> 	* tree-dfa.c (get_ref_base_and_extent): Likewise.
>
> gcc/testsuite/ChangeLog:
>
> 	* gfortran.dg/unknown_commons.f: New.

Ping.

(Besides my original patch 
https://gcc.gnu.org/ml/gcc-patches/2016-02/msg01356.html which we decided was 
too fragile, I believe this is the only patch proposed that actually fixes the 
miscompare in 416.gamess.)

Thanks, Alan