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[Bug rtl-optimization/16802] PowerPC - Unnecessary extsw
- From: "nathan at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 3 Nov 2004 11:29:38 -0000
- Subject: [Bug rtl-optimization/16802] PowerPC - Unnecessary extsw
- References: <20040728170038.16802.steinmtz@us.ibm.com>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Additional Comments From nathan at gcc dot gnu dot org 2004-11-03 11:29 -------
I believe this is a problem with the tree optimizers being ABI blind. on 64bit
ppc integral parameters and return values are correctly extended to 64 bits. This
sign extension is inserted during the tree->rtl translation, and therefore
cannot leverage any ssa-vrp information. Unfortunately RTL does not have VRP
itself, but only condition-code propagation. Combine does not track values
across basic blocks, so it too is blind in this case, as the register is
written in two blocks.
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16802