https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101469
--- Comment #2 from Valeriy E. Ushakov <uwe at netbsd dot org> ---
I don't have the latest gcc handy, but I see this bug already in an old netbsd
tree from about an year ago with gcc 8.4.0
As hgutch@n.o pointed out, this seems to be a problem with this peephole2:
;; mov r12,r0
;; add #-48,r0 -> add #-48,r12
;; mov.l r0,@(4,r10) mov.l r12,@(4,r10)
;; (r12 dead)
(define_peephole2
[(set (match_operand:SI 0 "arith_reg_dest")
(match_operand:SI 1 "arith_reg_dest"))
(set (match_dup 0) (plus:SI (match_dup 0)
(match_operand:SI 2 "const_int_operand")))
(set (match_operand:SI 3 "general_movdst_operand") (match_dup 0))]
as far as I can tell, it optimizes
r0 = r2
r0 += 64
*(r0+4) = r0
to
r2 += 64
*(r0+4) = r2
failing to notice that the the destination uses r0 too.
Then in the cprop-registers step that r0 is replaced with r12 b/c of r0 = r12
done a bit earlier.
