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Re: [RFC] Removal of loop notes

Zdenek Dvorak wrote:

here is a proposal for the patch to remove loop notes (I still need to
benchmark it, and probably split into smaller parts).  However, I do not
understand some of the code from that it removes loop note usage, so I
would appreciate comments on them:

cse.c:cse_end_of_basic_block -- something related to jump following.
  Steven, you had some patches towards removing this, right?

While the unreviewed fwprop patches make jump following unnecessary, I probably won't argue for its removal until 4.3.

The code in question is just looking for the last instruction in the preceding basic block. If it does not find a NOTE_INSN_LOOP_END note, it will find a non-note just before it. If you really want to be sure, you may want to look for a NOTE_INSN_BASIC_BLOCK_BEG note instead.

For the -fcse-follow-jumps case, we'll find a BARRIER after the LOOP_END note. For the -fcse-skip-blocks case, we're only looking for a non-label and in this case the basic-block-beginning note should do the same function as the LOOP_END note.

CCing Joern because he seems to have used this stuff in the SH back-end, and can probably help understanding this code too.


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