Possible regression in DF analysis

[Claudiu Zissulescu Ianculescu]

It looks like that. The df_analyze_loop is only looking at the loop
BBs, and it is not clear for me if df_analyze_loop is required to have
all the df_live_outs correctly computed or not. Do you know if it is
true?

If the df_analyze_loop is not supposed to compute all the df_live_outs
correctly, then the error resides in how loop-doloop is using the
iv_analysis_loop_init().

Thank you for your help,
Claudiu

On Tue, Dec 13, 2022 at 10:41 AM Eric Botcazou <botcazou@adacore.com> wrote:
>
> > The problem shows in loop-doloop.c when I introduce a loop end pattern
> > that replaces the first jump instruction (JUMP_INSN 15) with a pattern
> > that clobbers CC reg. However, the DF doesn't look like it works as
> > the doloop step cannot find the CC reg alive. Please see
> > loop-doloop.c:766. Hence, it introduces the doloop_end patterns, and
> > renders the compare instruction (INSN 14) dead code. leading to
> > errors.
>
> So df_get_live_out does not contain the CC register?  iv_analysis_loop_init
> only performs a local update of the DF information, maybe it does not cover
> the basic block containing insn 14 and 15?
>
> --
> Eric Botcazou
>
>