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[Bug rtl-optimization/45434] x86 missed optimization: use high register (ah, bh, ch, dh) when available to make comparisons
- From: "ebotcazou at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 29 Aug 2010 19:12:39 -0000
- Subject: [Bug rtl-optimization/45434] x86 missed optimization: use high register (ah, bh, ch, dh) when available to make comparisons
- References: <bug-45434-17273@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla 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