[Bug optimization/14753] [tree-ssa] some missed forward propagation opportunities

["law at redhat dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From law at redhat dot com  2004-05-04 19:04 -------
Subject: Re:  [tree-ssa] some missed forward 
 propagation opportunities

In message <20040331024237.14588.qmail@sources.redhat.com>, "kazu at cs dot uma
ss dot edu" writes:
 >
 >------- Additional Comments From kazu at cs dot umass dot edu  2004-03-31 02:
 >42 -------
 >One more case.
 >
 >void bar (void);
 >
 >void
 >foo (unsigned int a)
 >{
 >  if ((a >> 5) & 1)
 >    bar ();
 >}
 >
 >I get:
 >
 >foo (a)
 >{
 >  _Bool T.2;
 >  unsigned int T.1;
 >  unsigned int T.0;
 >
 ><bb 0>:
 >  T.0_2 = a_1 >> 5;
 >  T.1_3 = T.0_2 & 1;
 >  T.2_4 = (_Bool)T.1_3;
 >  if (T.2_4) goto <L0>; else goto <L1>;
 >
 ><L0>:;
 >  bar () [tail call];
 >
 ><L1>:;
 >  return;
 >
 >}
 >
 >We could have "if (T.1_3 != 0)".
 >If nothing else, we can eliminate one temporary variable.
Well, not only do we get to eliminate a temporary, we then have the ability
to propagate T.1_3 == 0 on one arm of the branch.

It's a pretty trivial extension to the existing forward propagation code
[ It's the inversion of propagating from a TRUTH_NOT_EXPR. ]

On hold pending a merge into the mainline.

jeff




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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14753