Re: 'walk_stmt_load_store_addr_ops' for non-'gimple_assign_single_p (stmt)'

[Thomas Schwinge <thomas@codesourcery.com>]

Hi!

Richard, thanks for your answer.  I'll need to look into this more; two
questions already:

On 2021-03-15T20:17:17+0100, Richard Biener via Gcc <gcc@gcc.gnu.org> wrote:
> On March 15, 2021 7:31:46 PM GMT+01:00, Thomas Schwinge <thomas@codesourcery.com> wrote:
>>First time I'm using this API -- so the error certainly may be on my
>>side.  ;-)
>>
>>What I'm doing, is a 'walk_gimple_seq', and in that one's
>>'callback_stmt', call 'walk_stmt_load_store_addr_ops', to collect
>>variable load/store/address-taken instances.  This did seem quite
>>straight-forward, given the description; 'gcc/gimple-walk.c':
>>
>>/* For the statement STMT call the callbacks VISIT_LOAD, VISIT_STORE
>>and
>>      VISIT_ADDR if non-NULL on loads, store and address-taken operands
>>passing the STMT, the base of the operand, the operand itself
>>containing
>>  the base and DATA to it.  The base will be either a decl, an indirect
>>     reference (including TARGET_MEM_REF) or the argument of an address
>>       expression.
>>       Returns the results of these callbacks or'ed.  */
>>
>>    bool
>>    walk_stmt_load_store_addr_ops (gimple *stmt, void *data,
>>                               walk_stmt_load_store_addr_fn visit_load,
>>                              walk_stmt_load_store_addr_fn visit_store,
>>                               walk_stmt_load_store_addr_fn visit_addr)
>>    { [...] }
>>
>>Indeed, given (Fortran) 'zzz = 1', we produce GIMPLE:
>>
>>    gimple_assign <real_cst, zzz, 1.0e+0, NULL, NULL>
>>
>>..., and calling 'walk_stmt_load_store_addr_ops' on that, I see, as
>>expected, the 'visit_store' callback invoked, with 'rhs' and 'arg':
>>'<var_decl zzz>'.
>>
>>However, given (Fortran) 'zzz = r + r2', we produce GIMPLE:
>>
>>    gimple_assign <plus_expr, zzz, r, r2, NULL>
>>
>>..., and calling 'walk_stmt_load_store_addr_ops' on that, I see,
>>unexpectedly, no callback at all invoked: neither 'visit_load', nor
>>'visit_store' (nor 'visit_address', obviously).
>
> The variables involved are registers. You only get called on memory operands.

How would I have told that from the 'walk_stmt_load_store_addr_ops'
function description?  (How to improve that one "to reflect relatity"?)

But 'zzz' surely is the same in 'zzz = 1' vs. 'zzz = r + r2' -- for the
former I *do* see the 'visit_store' callback invoked, for the latter I
don't?

>From a quick look at 'gcc/gimple-walk.c:walk_stmt_load_store_addr_ops',
>>this seems to intentionally be implemented in this way -- but I don't
>>understand the rationale?
>>
>>
>>Instead of 'walk_gimple_seq' -> 'callback_stmt' ->
>>'walk_stmt_load_store_addr_ops', do I need to use 'walk_gimple_seq' ->
>>'callback_op' -> "something"?
>
> Yes, if you want to visit register sets and uses as a well. Note you'll also see constants that way.

I'll look into that; in particular to figure out "something" for what I
need: load/store/address-taken.


Grüße
 Thomas
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