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Subject: Re: [lno] [RFC] if-conversion and auto vectorizer
From: Diego Novillo <dnovillo@redhat.com>
To: Devang Patel <dpatel@apple.com>
Cc: Richard Henderson <rth@redhat.com>,
        "gcc@gcc.gnu.org list" <gcc@gcc.gnu.org>
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On Mon, 2004-03-15 at 19:01, Devang Patel wrote:

> > 	if (test)
> > 	   T_1 = *p;
> > 	else
> > 	   T_2 = 0;
> > 	T_3 = PHI (T_1, T_2);
> >
> > cannot be transformed to
> >
> > 	T_1 = *p;
> > 	T_3 = test ? T_1 : 0;
> > unless you can show either that (1) dereferencing *p will never trap,
> > or (2) some other dereference of *p dominates this test.  Similar
> > examples can be shown with arithmetic such as divide, or fp arithmetic
> > without -ffast-math (i.e. when we can't discount NaNs).
> 
> We also need to consider possible side effects of 'test' itself.
> 
Not in GIMPLE.  If 'test' is used in a predicate like the above, it
should be a GIMPLE scalar.


Diego.