[Bug rtl-optimization/33928] [4.3/4.4/4.5 Regression] 30% performance slowdown in floating-point code caused by r118475

[bonzini at gnu dot org]

------- Comment #84 from bonzini at gnu dot org  2009-05-15 10:35 -------
Ok, I am working on a patch to add a multiple-definitions DF problem and use
that together with a domwalk to find the single definitions (instead of
reaching-definitions, which is the remaining slow part).  The new problem has a
bitvector sized by the number of registers rather than the number of defs (that
is sized like the bitvectors for liveness), which means it will be fast.  It is
defined as follows:

MDkill (B) = regs that have a def in B
MDinit (B) = (union of MDkill (P) for every P : B \in DomFrontier(P) \cap
LRin(B)
MDin (B) = MDinit (B) \cup (union of MDout (P) for every predecessor P of B)
MDout (B) = MDin (B) - MDkill (B)


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33928