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[Bug tree-optimization/65709] [5 Regression] Bad code for LZ4 decompression with -O3 on x86_64
- From: "rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Thu, 09 Apr 2015 08:02:34 +0000
- Subject: [Bug tree-optimization/65709] [5 Regression] Bad code for LZ4 decompression with -O3 on x86_64
- Auto-submitted: auto-generated
- References: <bug-65709-4 at http dot gcc dot gnu dot org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65709
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target| |x86_64-*-*
Target Milestone|--- |5.0
--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
*(U64*)dstPtr = *(U64*)srcPtr;
makes GCC assume that dstPtr and srcPtr are suitably aligned for U64, if they
are not then you invoke undefined behavior. As x86 doesn't trap on unaligned
accesses unless they are from vectorized code this shows up only when the
vectorizer exploits that alignment info.
Thus I'd say this bug is invalid.