http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55025
Bug #: 55025
Summary: reg_nonzero_bits_for_combine/get_last_value: missing
mode check for hardware registers
Classification: Unclassified
Product: gcc
Version: 4.6.3
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: aurelien.buhrig....@gmail.com
Created attachment 28511
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=28511
patch
This bug occurs with gcc 4.6.3 for a private backend (big endian), but should
occurs on trunk. The testcase is pr27364.c, compiled with -Os.
In the following RTL, the hardware register (reg:HI r2), whose natural mode is
HImode, is set to 0, but when combining insn 12 and insn 13 insn (during
combine pass), the (reg:SI r2) is computed to be equivalent to
(const_int 0), which is wrong (it is (reg:HI r2) which is (const_int 0)).
(insn 51 9 52 3 (set (reg:HI 2 r2)
(const_int 0 [0])) gcc.c-torture/execute/pr27364.c:5 18 {*movhi1}
(expr_list:REG_DEAD (reg:HI 31)
(expr_list:REG_EQUAL (const_int 0 [0])
(nil))))
(insn 52 51 12 3 (set (reg:HI 3 r3 [orig:2+2 ] [2])
(reg/v:HI 20 [ number_of_digits_to_use ]))
gcc.c-torture/execute/pr27364.c:5 18 {*movhi1}
(expr_list:REG_DEAD (reg/v:HI 20 [ number_of_digits_to_use ])
(nil)))
(insn 12 52 13 3 (set (reg:SI 0 r0)
(const_int 3321928 [0x32b048]))
gcc.c-torture/execute/pr27364.c:5 19 {movsi}
(nil))
(insn 13 12 16 3 (parallel [
(set (reg:SI 0 r0)
(mult:SI (reg:SI 2 r2)
(reg:SI 0 r0)))
(clobber (reg:SI 2 r2))
]) gcc.c-torture/execute/pr27364.c:5 54 {*mulsi3_call}
(expr_list:REG_EQUAL (mult:SI (reg:SI 2 r2)
(const_int 3321928 [0x32b048]))
(expr_list:REG_DEAD (reg:HI 3 r3)
(expr_list:REG_UNUSED (reg:SI 2 r2)
(nil)))))
The problem comes from a missing mode check in both
reg_nonzero_bits_for_combine and get_last_value.
See http://gcc.gnu.org/ml/gcc/2012-10/msg00263.html for more information.
Note that the problem in get_last_value has already been reported (bug 49884).
The attached patch fixes the issue in gcc-4.6.3. Not yet boostraped on trunk.
