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GCC 4.8 and -ftree-loop-distribute-patterns.
- From: "Carlos O'Donell" <carlos at redhat dot com>
- To: GNU C Library <libc-alpha at sourceware dot org>
- Date: Thu, 14 Feb 2013 15:56:34 -0500
- Subject: GCC 4.8 and -ftree-loop-distribute-patterns.
Team,
In GCC 4.8 we now have -ftree-loop-distribute-patterns enabled at -O3.
This optimization is unsafe in glibc. The optimization detects code
patterns that match specific runtime functions and converts the code
into a function call e.g. Call to memset for a loop that iterates over
memory setting a value.
We're already seeing the optimization breaking Fedora rawhide builds.
I'm thinking we could unconditionally disable this optimization for
elf/ and string/ subdirs?
Where else are we going to need to disable this optimization?
Do we need to detect GCC 4.8 and then add -fno-tree-loop-distribute-patterns?
Cheers,
Carlos.