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

Alan Lawrence alan.lawrence@foss.arm.com
Mon Feb 22 11:46:00 GMT 2016

On 19/02/16 17:52, Jakub Jelinek wrote:
> On Fri, Feb 19, 2016 at 05:42:34PM +0000, Alan Lawrence wrote:
>> This relates to FORTRAN code where different modules give different sizes to the
>> same array in a COMMON block (contrary to the fortran language specification).
>> SPEC have refused to patch the source code
>> (https://www.spec.org/cpu2006/Docs/faq.html#Run.05).
>> Hence, this patch provides a Fortran-specific option -funknown-commons that
>> marks such arrays as having unknown size - that is, NULL_TREE for both
>> TYPE_SIZE and max value of TYPE_DOMAIN. DECL_SIZE is preserved for e.g. output
>> in varasm.c.
>> On AArch64, it fixes the 416.gamess issue, and allows compiling 416.gamess
>> without the -fno-aggressive-loop-optimizations previously required (numerous
>> other PRs relating to 416.gamess).
>> I had to fix up a couple of places to deal with null TYPE_SIZE but in most cases
> I think it is wrong to touch TYPE_SIZE/TYPE_SIZE_UNIT, IMHO it is much better just
> to ignore DECL_SIZE/DECL_SIZE_UNIT in the selected few places
> (get_ref_base_and_extent, the tree-ssa-loop-niters.c analysis) if the switch
> is on, for selected decls (aggregates with flexible array members and other
> similar trailing arrays, arrays themselves; all only if DECL_COMMON).

So do you see...

(a) A global command-line option, which we check alongside DECL_COMMON, in (all 
or some of the) places which currently deal with flexible array members? (I 
guess the flag would have no effect for compiling C code...or
  (b) do we require it to 'enable' the existing flexible array member support?)

(c) A new flag on each DECL, which we check in the places dealing with flexible 
array members, which we set on those decls in the fortran frontend if a 
fortran-frontend-only command-line option is passed?

(d) A new flag on each DECL, which replaces the check for flexible array 
members, plus a global command-line option, which controls both setting the flag 
(on DECL_COMMONs) in the fortran frontend, and also setting it on flexible array 
members in the C frontend? This might be 'cleanest' but is also probably the 
most change and I doubt I'm going to have time to do this for GCC 6...

(e) Some other scheme that I've not understood yet?


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