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[Bug target/20126] [3.3/3.4/4.0 Regression] Inlined memcmp makes one argument null on entry

------- Additional Comments From aoliva at gcc dot gnu dot org  2005-04-12 08:19 -------
Subject: Re: [PR target/20126, RFC] loop DEST_ADDR biv replacement may fail

On Apr 12, 2005, Alexandre Oliva <> wrote:

> They are optimized away, but if I can figure out what the
> conditions are in which we don't need to introduce assignments to the
> giv, we could simply avoid all the messy new code, that assumes we
> absolutely must replace the expression with something else.

It appears that the only case in which we could do away with adding
the assignment is if giv->same is biv, and we mark the bl with
all_reduced=0.  It appears to me that, in any other case, the
assignment we're relying on might have been dropped or hoisted.

I'd love to be wrong, though.  If I am, we could get your problem, as
well as the original bug report, fixed by simply reverting my patch
and setting bl->all_reduced=0 if validate_change failed.  This
actually works for the testcases I've tried, but I'm not convinced it
works in the general case.  Does any expert in rtl loop care to chime



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