[Bug rtl-optimization/81019] [6/7/8 Regression] wrong code with -O -fno-tree-ccp

[aoliva at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81019

--- Comment #5 from Alexandre Oliva <aoliva at gcc dot gnu.org> ---
Author: aoliva
Date: Mon Dec 11 22:36:07 2017
New Revision: 255554

URL: https://gcc.gnu.org/viewcvs?rev=255554&root=gcc&view=rev
Log:
[PR80693] drop value of parallel SETs dropped by combine

When combine drops a REG_UNUSED SET in a parallel, we have to clear
cached values, so that, even if the REGs remain used (e.g. because
they were referenced in the used SET_SRC), we will not use properties
of the dropped modified value as if they applied to the preserved
original one.

We fail to adjust REG_N_SETS.

for  gcc/ChangeLog

        PR rtl-optimization/80693
        PR rtl-optimization/81019
        PR rtl-optimization/81020
        * combine.c (distribute_notes): Reset any REG_UNUSED REGs that
        are not mentioned in i3.  Place the REG_UNUSED note on i2,
        possibly modified to REG_DEAD, if it did not originate in i3.

for  gcc/testsuite/ChangeLog

        PR rtl-optimization/80693
        PR rtl-optimization/81019
        PR rtl-optimization/81020
        * gcc.dg/pr80693.c: New.
        * gcc.dg/pr81019.c: New.

Added:
    trunk/gcc/testsuite/gcc.dg/pr80693.c
    trunk/gcc/testsuite/gcc.dg/pr81019.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/combine.c
    trunk/gcc/testsuite/ChangeLog