https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66412
--- Comment #3 from Uroš Bizjak <ubizjak at gmail dot com> ---
This testcase exposes latent problem in combine pass in conjunction with debug.
We start with:
[...]
(insn 8 7 9 2 (set (reg:QI 95)
(eq:QI (reg:CCZ 17 flags)
(const_int 0 [0]))) pr66412.c:9 597 {*setcc_qi}
(expr_list:REG_DEAD (reg:CCZ 17 flags)
(nil)))
(insn 9 8 11 2 (set (reg:SI 94 [ D.1784 ])
(zero_extend:SI (reg:QI 95))) pr66412.c:9 134 {*zero_extendqisi2}
(expr_list:REG_DEAD (reg:QI 95)
(nil)))
(debug_insn 11 9 12 2 (var_location:HI g (subreg:HI (reg:SI 94 [ D.1784 ]) 0))
pr66412.c:9 -1
(nil))
(debug_insn 12 11 13 2 (var_location:HI e (subreg:HI (ashift:SI (reg:SI 94 [
D.1784 ])
(const_int 1 [0x1])) 0)) pr66412.c:10 -1
(nil))
(insn 13 12 14 2 (parallel [
(set (reg:SI 96 [ D.1783 ])
(ashift:SI (reg:SI 94 [ D.1784 ])
(const_int 1 [0x1])))
(clobber (reg:CC 17 flags))
]) pr66412.c:11 501 {*ashlsi3_1}
(expr_list:REG_DEAD (reg:SI 94 [ D.1784 ])
(expr_list:REG_UNUSED (reg:CC 17 flags)
(nil))))
(insn 14 13 15 2 (set (reg:CCZ 17 flags)
(compare:CCZ (subreg:HI (reg:SI 96 [ D.1783 ]) 0)
(const_int 0 [0]))) pr66412.c:11 2 {*cmphi_ccno_1}
(expr_list:REG_DEAD (reg:SI 96 [ D.1783 ])
(nil)))
(insn 15 14 16 2 (set (reg:QI 98)
(ne:QI (reg:CCZ 17 flags)
(const_int 0 [0]))) pr66412.c:11 597 {*setcc_qi}
(expr_list:REG_DEAD (reg:CCZ 17 flags)
(nil)))
[...]
and combine pass sequentially combines several insns into (insn 15):
Trying 8 -> 9:
Successfully matched this instruction:
(set (reg:SI 94 [ D.1784 ])
(eq:SI (reg:CCZ 17 flags)
(const_int 0 [0])))
allowing combination of insns 8 and 9
original costs 4 + 4 = 8
replacement cost 4
deferring deletion of insn with uid = 8.
modifying insn i3 9: r94:SI=flags:CCZ==0
REG_DEAD flags:CCZ
deferring rescan insn with uid = 9.
Trying 13 -> 14:
Successfully matched this instruction:
(set (reg:CCZ 17 flags)
(compare:CCZ (ashift:SI (reg:SI 94 [ D.1784 ])
(const_int 1 [0x1]))
(const_int 0 [0])))
allowing combination of insns 13 and 14
original costs 4 + 4 = 8
replacement cost 4
deferring deletion of insn with uid = 13.
modifying insn i3 14: {flags:CCZ=cmp(r94:SI<<0x1,0);clobber scratch;}
REG_DEAD r94:SI
deferring rescan insn with uid = 14.
Trying 9, 14 -> 15:
Failed to match this instruction:
(set (reg:QI 98)
(ne:QI (eq:SI (reg:CCZ 17 flags)
(const_int 0 [0]))
(const_int 0 [0])))
Splitting with gen_split_5441
Successfully matched this instruction:
(set (reg:QI 98)
(eq:QI (reg:CCZ 17 flags)
(const_int 0 [0])))
allowing combination of insns 9, 14 and 15
original costs 4 + 4 + 4 = 12
replacement cost 4
deferring deletion of insn with uid = 14.
Calling propagate_for_debug for:
(debug_insn 11 9 12 2 (var_location:HI g (subreg:HI (reg:SI 94 [ D.1784 ]) 0))
pr66412.c:9 -1
(nil))
we found (wrong) replacement for (reg:SI 94):
(eq:QI (reg:CCZ 17 flags)
(const_int 0 [0]))
and we try to call simplify_gen_subreg with:
(gdb) f 3
#3 0x0000000000aa2aaa in simplify_gen_subreg (outermode=HImode,
op=0x7ffff12aff00, innermode=SImode, byte=0) at
/home/uros/gcc-svn/trunk/gcc/simplify-rtx.c:5969
5969 newx = simplify_subreg (outermode, op, innermode, byte);
(gdb) p debug_rtx (op)
(eq:QI (reg:CCZ 17 flags)
(const_int 0 [0]))
which crashes at:
#2 0x0000000000aa261a in simplify_subreg (outermode=HImode, op=0x7ffff12aff00,
innermode=SImode, byte=0) at /home/uros/gcc-svn/trunk/gcc/simplify-rtx.c:5749
5749 gcc_assert (GET_MODE (op) == innermode
