On 9/30/22 04:47, Richard Sandiford wrote:
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)?
Right. Different pseudos used in the comparison vs the destination of
the assignment. If they used the same pseudo, then I would have
expected cse or gcse to pick it up.
+ /* 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))
?
Looks like a mistake to me. we don't want to process anything for a
successor of the entry block. I'll adjust and retest.
Thanks,
Jeff
