https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110531
Kewen Lin <linkw at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |rguenth at gcc dot gnu.org
--- Comment #1 from Kewen Lin <linkw at gcc dot gnu.org> ---
(In reply to Hao Liu from comment #0)
> This seems an obvious bug in tree-vect-loop.cc:
>
> (1) This var is declared (but not initialized) and used in function
> vect_analyze_loop_1:
>
> bool slp_done_for_suggested_uf; <---- Warning, this is not
> initialized
>
> /* Run the main analysis. */
> opt_result res = vect_analyze_loop_2 (loop_vinfo, fatal,
> &suggested_unroll_factor,
> slp_done_for_suggested_uf);
>
> (2) It is used before set in function vect_analyze_loop_2:
> static opt_result
> vect_analyze_loop_2 (loop_vec_info loop_vinfo, bool &fatal,
> unsigned *suggested_unroll_factor,
> bool& slp_done_for_suggested_uf)
> ...
> bool slp = !applying_suggested_uf || slp_done_for_suggested_uf; <--- used
> without initialized
> ...
> slp_done_for_suggested_uf = slp;
>
>
> I don't know the detail logic and wonder if it should be initialized as
> "true" or "false" (probably it should be "false").
Is the warning from some static analyzer?
This behavior was intentional, in the first time to call vect_analyze_loop_2,
we have loop_vinfo->suggested_unroll_factor = 1, applying_suggested_uf would be
false always, it means that at the below place
bool slp = !applying_suggested_uf || slp_done_for_suggested_uf;
slp should be true always (always do analyze slp), it doesn't care what's in
slp_done_for_suggested_uf.
For a successful analysis, we would definitely do:
slp_done_for_suggested_uf = slp;
So in the 2nd call to vect_analyze_loop_2, slp_done_for_suggested_uf should get
assigned by expected valu (should not be uninitialized).
