Re: [RFC] Removal of loop notes

[Paolo Bonzini <paolo dot bonzini at lu dot unisi dot ch>]

Zdenek Dvorak wrote:
> Hello,
>
> 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.

Paolo