[Bug middle-end/70189] New: Combine constant-pool logic from gimplify + SRA

alalaw01 at gcc dot gnu.org gcc-bugzilla@gcc.gnu.org
Fri Mar 11 14:45:00 GMT 2016


https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70189

            Bug ID: 70189
           Summary: Combine constant-pool logic from gimplify + SRA
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: alalaw01 at gcc dot gnu.org
  Target Milestone: ---

Following PR/63679 (r232506), gimplify.c (gimplify_init_constructor) uses lots
of heuristics to choose between pushing initializers out to the constant pool
(by calling tree_output_constant_def) or outputting many elementwise
statements. Then, in tree-sra.c (analyze_all_variable_accesses), we use more
heuristics to decide which constant-pool loads to completely_scalarize, 
turning those back into elementwise statements. (These get pulled back in from
the constant pool and the constant-pool entry deleted.) Both of these sets of
heuristics are platform dependent (gimplify.c uses can_move_by_pieces,
CLEAR_RATIO; tree-sra.c uses get_move_ratio).

Instead we should put all this logic in one place; this would make it clearer,
and we'd probably get better overall decisions. The suggestion is for
gimplify.c to always push out to the constant pool, as this makes initial tree
the same on all platforms, and for all the logic/heuristics to go into SRA (as,
being later, we then have more information available to maybe make better
decisions in the future).


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