PATCH to remove unnecessary NOTE_INSN_DELETED

Bernd Schmidt bernds@cygnus.co.uk
Tue Nov 30 23:59:00 GMT 1999


On Thu, 4 Nov 1999, Jeffrey A Law wrote:
>   In message < Pine.LNX.4.10.9911041808370.6182-100000@biriani.cygnus.co.uk >you 
> write:
>   > Just FYI, I started to look into this.  I've hit one stumbling block so far
>   > (expressions of the form uid_luid[REGNO_FIRST_UID (xxx)], but I guess that
>   > can be worked around somehow.
> Instead of recording the UID record the actual insn perhaps.

That breaks down if the insn gets deleted (loop has some code to deal with
that problem by making uid_luid "approximately right" for insns that have been
deleted).

> Or if we relax the "luids are for within a pass only" decree slightly we
> could go ahead and record the first/last luid in regscan.

That might work better.
Apart from those problems, the mechanisms used e.g. in loop which involve
comparisons between insn uids/luids to determine which insn is executed first
seem exceedingly brittle; I suspect it might not be hard to fool parts of the
loop optimizer with clever use of gotos.

Bernd



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