http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52272
bin.cheng <amker.cheng at gmail dot com> changed:
What |Removed |Added
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CC| |amker.cheng at gmail dot com
--- Comment #21 from bin.cheng <amker.cheng at gmail dot com> ---
Hi Richard,
I looked into PR50955 for which the mentioned commit causing this PR is
applied:
Commit
2012-02-06 Richard Guenther <[email protected]>
PR tree-optimization/50955
* tree-ssa-loop-ivopts.c (get_computation_cost_at): Artificially
raise cost of expressions that replace an address with an
expression based on a different pointer.
I noticed that the offending non-linear use in PR50955 is actually from memory
reference. If I understand the issue correct, the whole alias issue is
introduced by rewriting iv use with one base_object through candidate with
another incompatible base_object, and it is related to memory reference. An
genuine non-linear iv use (the pointer never de-referenced, like in this PR)
won't have this issue.
So I come up this idea to relax the condition:
- if (address_p)
+ if (address_p
+ || (use->iv->base_object
+ && cand->iv->base_object
+ && POINTER_TYPE_P (TREE_TYPE (use->iv->base_object))
+ && POINTER_TYPE_P (TREE_TYPE (cand->iv->base_object))))
{
/* Do not try to express address of an object with computation based
on address of a different object. This may cause problems in rtl
to non-linear uses which truly occurred in memory reference, something like:
- if (address_p)
+ if (address_p
+ || (use->in_mem_ref_p
+ && use->iv->base_object
+ && cand->iv->base_object
+ && POINTER_TYPE_P (TREE_TYPE (use->iv->base_object))
+ && POINTER_TYPE_P (TREE_TYPE (cand->iv->base_object))))
{
/* Do not try to express address of an object with computation based
on address of a different object. This may cause problems in rtl
The flag in_mem_ref_p can be set for appropriate uses when finding interesting
address uses.
With this change, this PR should be resolved while not violating PR50955.
I am not very much into 50955, so how does this sound? I can send a patch for
review if the idea is in right direction.
BTW, I cannot reproduce 50955 with the reported revision of GCC. The store
isn't deleted by pass_cd_dce, though it is re-written just as the PR reported.
So maybe I just misunderstood something.
Any words?
Thanks,
bin
