[Bug rtl-optimization/53533] [4.7/4.8 regression] vectorization causes loop unrolling test slowdown as measured by Adobe's C++Benchmark

[rth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53533

Richard Henderson <rth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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             Status|NEW                         |ASSIGNED

--- Comment #16 from Richard Henderson <rth at gcc dot gnu.org> 2012-06-14 
18:38:30 UTC ---
Dunno exactly.  The pre-SSE4.1 emulation of PMULLD has been there since
at least gcc 4.5.

What's not present in *any* version so far are some proper rtx_costs for
integer vector operations.  So any questions the vectorizer might be
asking about what transformations are profitable are currently being
given bogus answers.

I'm hoping just that will fix the regression, though I also plan to
address some of the other algorithmic questions raised in this PR.