[Bug tree-optimization/29680] [4.3 Regression] Misscompilation of spec2006 gcc

[dnovillo at gcc dot gnu dot org]

------- Comment #30 from dnovillo at gcc dot gnu dot org  2006-11-09 19:48 -------
(In reply to comment #29)

> nevertheless, it is not obvious to me whether using mem-ssa over Daniel's
> proposal would bring any significant gains, which I would like to have
> 
Of course.  If you are interested in the compile time benefits of a
partitioning scheme, you can actually try the one we already have by forcing
alias grouping more aggressively (--param max-aliased-vops).

The current grouping is very dumb and will create tons of false positives. 
Daniel's approach will try to reduce false positives while bringing down the
number of virtual operators per memory statement.

Memory SSA brings down the number of virtual operators to exactly one per
statement.


> verified before we introduce milion new bugs with mem-ssa (nothing
> personal, it simply is too large and too intrusive change not to bring
> any).
>
Intrusive?  Well, the only pass that was wired to the previous virtual operator
scheme was PRE.  DSE is also wired but to a lesser extent.  No other
optimization had to be changed for mem-ssa.  It's obviously intrusive in the
renamer, but that's it.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29680