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Re: Fix RTL sharing found during PPC bootstrap


On Sunday 17 December 2006 16:48, roger@eyesopen.com wrote:
> It's because CSE,
> GCSE and cselib only track the values of pseudos, the RTL expanders
> try and place repeated expressions in their own registers, otherwise
> they wouldn't be able to detect that "SUBREG:SI (REG:SF)" was used
> repeatedly.

Actually, GCSE does not track values of pseudos.  Classic PRE eliminates
lexically equivalent expressions, but it can't track value equivalences.
We fail to eliminate a number of value-equivalent common sub-expressions
because they are not lexically equivalent.  In this case, the effort of
the RTL expanders is a bad thing.

Gr.
Steven


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