[Bug rtl-optimization/50904] Induct benchmark of polyhedron slows down when -fno-protect-parens is enabled by -Ofast.

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50904

Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:

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--- Comment #6 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2011-11-01 13:52:48 UTC ---
> I don't see why RTL invariant motion should move the one variant but not
> the other.  Of course this also shows that we should, after loop unrolling
> on the tree level, also perform loop invariant motion again ...

The problem seems to be in RTL PRE, which hoists simple loads but not loads
that are wrapped up in a PLUS or a MINUS.  Even with -fprotect-parens, load
hoisting opportunities are lost because of this.