https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63156
--- Comment #9 from Carrot <carrot at google dot com> ---
The original flag setting code is neither correct. Consider following
pre_modify expression:
(pre_modify (r1) // def1, use1
(plus (r1) // use2
(r2))) // use3
GCC will generate 4 df_ref information for this expression as noted, 1 def and
3 use. Current code only set DF_REF_READ_WRITE for def1, this causes web do
wrong renaming. The original flag setting code will set DF_REF_READ_WRITE for
all def/use in this expression, this is obviously wrong for r2.
I don't know if this has any relations to bug 32339.
