Jeff Law <j...@ventanamicro.com> writes:
> This is another minor improvement to coremark. I suspect this only
> improves code size as the load-immediate was likely issuing with the ret
> statement on multi-issue machines.
>
>
> Basically we're failing to utilize conditional equivalences during the
> post-reload CSE pass. So if a particular block is only reached when a
> certain condition holds (say for example a4 == 0) and the block has an
> assignment like a4 = 0, we would fail to eliminate the unnecessary
> assignment.
I wasn't sure (and was too lazy to try, sorry), but: is the reason
that we fail to catch this earlier because the two uses of r4 are
entirely separate (i.e. not from the same pseudo)?
> + /* Iterate over each incoming edge and see if they
> + all have the same implicit set. */
> + FOR_EACH_EDGE (e, ei, bb->preds)
> + {
> + /* If the predecessor does not end in a conditional
> + jump, then it does not have an implicit set. */
> + if (e->src != ENTRY_BLOCK_PTR_FOR_FN (cfun)
> + && !block_ends_with_condjump_p (e->src))
> + {
> + found = false;
> + break;
> + }
> +
> + /* We know the predecessor ends with a conditional
> + jump. Now dig into the actal form of the jump
> + to potentially extract an implicit set. */
Very minor, but it looked odd to fall through for the entry block.
How about:
if (e->src == ENTRY_BLOCK_PTR_FOR_FN (cfun)
|| !block_ends_with_condjump_p (e->src))
?
> + rtx_insn *condjump = BB_END (e->src);
> + if (condjump
> + && any_condjump_p (condjump)
> + && onlyjump_p (condjump))
> + {
> + /* Extract the condition. */
> + rtx pat = PATTERN (condjump);
> + rtx i_t_e = SET_SRC (pat);
> + gcc_assert (GET_CODE (i_t_e) == IF_THEN_ELSE);
> + rtx cond = XEXP (i_t_e, 0);
> + if ((GET_CODE (cond) == EQ
> + && GET_CODE (XEXP (i_t_e, 1)) == LABEL_REF
> + && XEXP (XEXP (i_t_e, 1), 0) == BB_HEAD (bb))
> + || (GET_CODE (cond) == NE
> + && XEXP (i_t_e, 2) == pc_rtx
> + && e->src->next_bb == bb))
> + {
> + /* If this is the first time through record
> + the source and destination. */
> + if (!dest)
> + {
> + dest = XEXP (cond, 0);
> + src = XEXP (cond, 1);
> + }
> + /* If this is not the first time through, then
> + verify the source and destination match. */
> + else if (dest == XEXP (cond, 0) && src == XEXP (cond, 1))
> + ;
FWIW, agree with what Richi said about using rtx_equal_p here. We don't
necessarily end up with shared hard regs, especially if they originated
from different pseudos.
Thanks,
Richard
