[Bug rtl-optimization/15023] -frename-registers is buggy and slow

[ebotcazou at gcc dot gnu dot org]

------- Additional Comments From ebotcazou at gcc dot gnu dot org  2005-08-04 09:04 -------
I'd like to mention a known problem with -frename-registers.  Quoting my
analysis for another bug report:

"However the underlying problem is still present and is now visible on x86-64:
the register renaming pass (regrename.c) uses its own life analysis engine to 
compute the def-use chains.  It turns out that it is less accurate than the 
all-purpose life analysis engine (flow.c) and, consequently, when the latter 
is invoked to update the global liveness info at the end of the pass, it may 
flag internal inconsistencies introduced because of the former.

It is not immediately obvious what the best approach to solving that would be.
A third life analysis engine exists (df.c) and is supposed to be modular, so 
we could try to plug it into regrename.c."

The typical example is PR rtl-optimization/16586.


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           What    |Removed                     |Added
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                 CC|                            |ebotcazou at gcc dot gnu dot
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  BugsThisDependsOn|                            |16586


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15023