cse_process_notes_1 issue ?

[Aurelien Buhrig]

Hi,

I'm trying to track a bug down on a private backend which occurs during
CSE pass (gcc-4.6.3, pr27364.c).

In the following RTL, the hardware (reg:HI r2), whose natural mode is
HImode, is set to 0, but when analysing the REG_EQUAL notes of the MULT
insn during CSE pass, the (reg:SI r2) is computed to be equivalent to 0,
which is wrong (the target is big endian).

(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)))))


I think a mode size check is missing when processing REG code in
cse_process_notes_1. Adding such a check prevents the CSE pass from
elimintating the MULT instruction.

But then this MULT insn is simplified during the combine pass:

Trying 12 -> 13:
...
Successfully matched this instruction:
(set (reg:SI 0 r0)
    (const_int 0 [0]))
deferring deletion of insn with uid = 12.
deferring deletion of insn with uid = 52.
modifying insn i3    13 r0:SI=0
deferring rescan insn with uid = 13.


So double middle-end bug or do I miss something?

Thanks,
Aurelien