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Re: RFA: Store the REG_BR_PROB probability directly as an int


Hello Richard,

Not directly related to your patch but...

On Sun, Sep 22, 2013 at 12:54 PM, Richard Sandiford wrote:
> @@ -588,14 +589,17 @@ cond_exec_process_if_block (ce_if_block_
>      goto fail;
>  #endif
>
> -  true_prob_val = find_reg_note (BB_END (test_bb), REG_BR_PROB, NULL_RTX);
> -  if (true_prob_val)
> +  note = find_reg_note (BB_END (test_bb), REG_BR_PROB, NULL_RTX);
> +  if (note)
>      {
> -      true_prob_val = XEXP (true_prob_val, 0);
> -      false_prob_val = GEN_INT (REG_BR_PROB_BASE - INTVAL (true_prob_val));
> +      true_prob_val = XINT (note, 0);
> +      false_prob_val = REG_BR_PROB_BASE - true_prob_val;
>      }
>    else
> -    false_prob_val = NULL_RTX;
> +    {
> +      true_prob_val = -1;
> +      false_prob_val = -1;
> +    }
>
>    /* If we have && or || tests, do them here.  These tests are in the adjacent
>       blocks after the first block containing the test.  */

You can just take true_prob_val and false_prob_val from the edge
probabilities of BRANCH_EDGE and FALLTHRU_EDGE.

Looking at REG_BR_PROB notes in places where the CFG is available is
IMHO always a bug. Other places where this happens are at least these:

loop-doloop.c:doloop_modify()
cfgrtl.c:force_nonfallthru_and_redirect()
cfgrtl.c:fixup_reorder_chain()

(Long-term I'd like to see REG_BR_PROB notes become redundant, by
extending the life of the CFG all the way to final...)

Ciao!
Steven


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