[Bug tree-optimization/23821] [4.0/4.1/4.2 Regression] DOM and VRP creating harder to optimize code

["sebastian dot pop at cri dot ensmp dot fr" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #8 from sebastian dot pop at cri dot ensmp dot fr  2006-02-13 08:45 -------
Subject: Re:  [4.0/4.1/4.2 Regression] DOM and VRP creating harder to optimize
code

This case reminds me the peeled chrec unification that I had to
disable on autovect branch (I probably have to run the transformation
as a stand alone pass outside the analyzer for not disturbing the user
passes).  In that case we're looking at a code like

loop
  x = phi (0, a)
  a = phi (1, a + 1)
endloop

such that a simple transformation can make "x" a simple iv.  This case
is also quite important, as it occurs about 300 times during a bootstrap.

Now for the current problem, we could run a pass just after loop_init
for cleaning all these constructs.  As suggested, we would have to
build an equivalence relation either like VRP, or on demand.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23821