I can only reproduce this problem on the sh target with a gcc version 3.4.3.
However my analysis makes me believe the problem still exists on the trunk.
After greg I have the following sequence :
(insn:HI 11 10 12 0 (set (reg/v/f:SI 2 r2 [orig:160 PrivateData_p ] [160])
(const_int 128 [0x80])) 122 {movsi_i} (nil)
(nil))
(insn:HI 12 11 134 0 (set (reg/v/f:SI 2 r2 [orig:160 PrivateData_p ] [160])
(plus:SI (reg/v/f:SI 2 r2 [orig:160 PrivateData_p ] [160])
(reg:SI 3 r3 [orig:162 Device_p ] [162]))) 23 {*addsi3_compact}
(insn_list 10 (insn_list 11 (nil)))
(expr_list:REG_EQUAL (plus:SI (reg:SI 3 r3 [orig:162 Device_p ] [162])
(const_int 128 [0x80]))
(nil)))
...
(insn:HI 16 135 17 0 (set (reg:SI 1 r1 [166])
(const_int 188 [0xbc])) 122 {movsi_i} (nil)
(nil))
(insn:HI 17 16 18 0 (set (reg:SI 1 r1 [166])
(plus:SI (reg:SI 1 r1 [166])
(reg/v/f:SI 2 r2 [orig:160 PrivateData_p ] [160]))) 23
{*addsi3_compact} (insn_list 16 (nil))
(expr_list:REG_EQUAL (plus:SI (reg:SI 3 r3 [orig:162 Device_p ] [162])
(const_int 316 [0x13c]))
(nil)))
'reload_combine' decides to optimize insns 16/17. After the optimisation, there
is a 'continue' and reload_combines tries other pattern.
The problem is that with this 'continue' reg_state[regno] was is updated with
the other uses (here r2).
later on insn 11/12 are optimized away, believing that r2 is dead because not
makrked in the reg_state use list, leaving it undefined.
The problem is very difficult to isolate (didn't succeed on trunk with i686)
but by reading the postreload code the bug seems latent.
--
Summary: sh postreload bug (might be generic in trunk)
Product: gcc
Version: 3.4.3
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: christian dot bruel at st dot com
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnugcc
GCC target triplet: sh-superh-elf-gcc
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30807
