Possible regression in DF analysis

Eric Botcazou botcazou@adacore.com
Tue Dec 13 08:41:32 GMT 2022


> 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




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