[Bug rtl-optimization/45434] x86 missed optimization: use high register (ah, bh, ch, dh) when available to make comparisons

[ebotcazou at gcc dot gnu dot org]

------- Comment #5 from ebotcazou at gcc dot gnu dot org  2010-08-29 19:12 
-------
> Combine seems to prefer LSHIFTRT over ZERO_EXTRACT.

The former is the canonical form of the latter for internal computations, but
the latter should be reinstantiated when matching instructions.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45434