On Thu, Oct 10, 2013 at 07:26:43AM -0700, Cesar Philippidis wrote:
This patch addresses an ICE when building qemu for a Mips target in
Yocto. Both gcc-trunk, gcc-4.8 and all of the targets are potentially
affected. The problem occurs because the instruction combine phase uses
two data structures to keep track of registers, reg_stat and
regstat_n_sets_and_refs, but they potentially end up out of sync; when
combine inserts a new register into reg_stat it does not update
regstat_n_sets_and_refs. Failing to update the latter results in an
occasional segmentation fault.
Is this OK for trunk and gcc-4.8? If so, please check it in. I tested it
on Mips and x86-64 and no regressions showed up.
That looks broken. You leave everything from the last size till the current
one uninitialized, so it would only work if combine_split_insns
always increments max_reg_num () by at most one.
Furthermore, there are macros which should be used to access
the fields, and, if the vector is ever going to be resized, supposedly
it should be vec.h vector rather than just array.
Or perhaps take into account:
/* If a pass need to change these values in some magical way or the
pass needs to have accurate values for these and is not using
incremental df scanning, then it should use REG_N_SETS and
REG_N_USES. If the pass is doing incremental scanning then it
should be getting the info from DF_REG_DEF_COUNT and
DF_REG_USE_COUNT. */
and not use REG_N_SETS etc. but instead the df stuff.