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r242059 - in /trunk/gcc: ChangeLog combine.c
- From: segher at gcc dot gnu dot org
- To: gcc-cvs at gcc dot gnu dot org
- Date: Thu, 10 Nov 2016 22:45:42 -0000
- Subject: r242059 - in /trunk/gcc: ChangeLog combine.c
Date: Thu Nov 10 22:45:39 2016
New Revision: 242059
combine: Do not call simplify from inside change_zero_ext (PR78232)
When combine splits a three-insn combination into two instructions it
can reuse i2dest for the temporary result of the first new instruction.
However all information it has in reg_stat about that register will be
stale. This results in the simplify_gen_binary calls in change_zero_ext
using out-of-date information, which makes it think one of the ANDs
generated there always results in 0, and it doesn't get better from there.
This can also happen if a splitter in the MD uses nonzero_bits (for
example). I tried to make the splitting code in combine save and restore
the i2dest reg_stat info, but that causes one of the acats tests to fail.
This whole reg_stat thing needs an overhaul, and/or we shouldn't reuse
i2dest for unrelated purposes when splitting.
This patch changes change_zero_ext to do the expected simplifications
itself and not call simplify_gen_*.
* combine.c (try_combine): Add a big comment about why reusing i2dest
(change_zero_ext): Do not call simplify_gen_binary, do the