On Wed, Jul 8, 2009 at 6:46 PM, Jeff Law<law@redhat.com> wrote:
After a clobber there should be no useful value in a pseudo until a later
set of the pseudo, so how does hoisting the clobber extend a pseudo's
lifetime? ISTM that hoisting the clobber to the earliest possible point in
the insn stream should be decreasing lifetimes.
What am I missing?
Please see the "Gcc 3.1 performance regressions with respect to
2.95.3" thread from March 2002, including:
http://gcc.gnu.org/ml/gcc-patches/2002-03/msg01763.html
Some of this may have been fixed, but GCC was emitting naked CLOBBERS
with open-coded no-conflict blocks and other entertaining ways.