[Bug rtl-optimization/28812] RTL aliasing vs may_alias and structs

["amylaar at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #6 from amylaar at gcc dot gnu dot org  2007-04-23 19:37 -------
(In reply to comment #5)
> Fixed.
> 

I also see mayalias-2 failing with gcc 4.2 on arc at
-O3 -fomit-frame-pointer.
Life analysis finds a 'clever' way to initialize the pointer p
by copying the frame pointer and then using pre-decrement addressing.
The following rtl dump is from mayalias-2.c.134r.life2 ; note that
insn 13 is the store of 1, and insn 15 is the dependent load.
Because the address in insn 13 does not show the frame pointer explicitly,
fixed_scalar_and_varying_struct_p decides that 'p' is varying, and hence
the two memory accesses don't alias.

(insn:HI 42 7 8 2 (set (reg/v/f:SI 149 [ p ])
        (reg/f:SI 27 fp)) 12 {*movsi_insn} (nil)
    (nil))

(insn:HI 8 42 10 2 (set (mem/c/i:SI (pre_dec:SI (reg/v/f:SI 149 [ p ])) [3 a+0
S4 A32])
        (reg:SI 151)) 12 {*movsi_insn} (insn_list:REG_DEP_TRUE 7
(insn_list:REG_DEP_TRUE 42 (nil)))
    (expr_list:REG_DEAD (reg:SI 151)
        (expr_list:REG_INC (reg/v/f:SI 149 [ p ])
            (expr_list:REG_EQUAL (const_int 10 [0xa])
                (nil)))))

(note:HI 10 8 12 2 NOTE_INSN_DELETED)

(insn:HI 12 10 13 2 (set (reg:HI 152)
        (const_int 1 [0x1])) 7 {*movhi_insn} (nil)
    (nil))

(insn:HI 13 12 15 2 (set (mem/s/j:HI (reg/v/f:SI 149 [ p ]) [0 <variable>.x+0
S2 A16])
        (reg:HI 152)) 7 {*movhi_insn} (insn_list:REG_DEP_TRUE 10
(insn_list:REG_DEP_TRUE 12 (nil)))
    (expr_list:REG_DEAD (reg:HI 152)
        (expr_list:REG_DEAD (reg/v/f:SI 149 [ p ])
            (expr_list:REG_EQUAL (const_int 1 [0x1])
                (nil)))))

(insn:HI 15 13 16 2 (set (reg:SI 153 [ a ])
        (mem/c/i:SI (plus:SI (reg/f:SI 27 fp)
                (const_int -4 [0xfffffffc])) [3 a+0 S4 A32])) 12 {*movsi_insn}
(nil)
    (nil))


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28812