[Bug tree-optimization/23382] [4.1 Regression] tree-ssa-alias creates a new virtual variable for malloc each time may_alias is run (HEAP)

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

------- Additional Comments From dberlin at gcc dot gnu dot org  2005-08-14 03:40 -------
Subject: Re:  New: [4.1 Regression]
	tree-ssa-alias creates a new virtual variable for malloc each time
	may_alias is run (HEAP)

On Sun, 2005-08-14 at 03:36 +0000, pinskia at gcc dot gnu dot org wrote:
> ----
> In .alias1:
>   i.0_18 = i_1;
>   #   HEAP.7_46 = V_MAY_DEF <HEAP.7_22>;
>   b_6->a1[i.0_18] = i_1;
>   i.0_19 = i_1;
>   #   HEAP.8_47 = V_MAY_DEF <HEAP.8_23>;
>   c_8->a1[i.0_19] = i_1;
>   i_20 = i_1 + 1;
> 
> In .alias2:
>   #   HEAP.19_14 = V_MAY_DEF <HEAP.19_21>;
>   b_5->a1[i_65] = i_65;
>   #   HEAP.20_73 = V_MAY_DEF <HEAP.20_10>;
>   c_7->a1[i_65] = i_65;
>   i_20 = i_65 + 1;

Uh, so?

This is because we recompute all the alias info, which means we really
recompute the alias info.

> 
> ---
> I don't know how much harm in compile time does this hurt in normal code but we then keep on adding 
> them to clobbered variables:
>   #   HEAP.6_27 = V_MAY_DEF <HEAP.6_24>;
>   #   HEAP.7_28 = V_MAY_DEF <HEAP.7_25>;
>   #   HEAP.8_29 = V_MAY_DEF <HEAP.8_26>;
>   #   HEAP.18_6 = V_MAY_DEF <HEAP.18_9>;
>   #   HEAP.19_8 = V_MAY_DEF <HEAP.19_64>;
>   #   HEAP.20_1 = V_MAY_DEF <HEAP.20_4>;
>   a_3 = malloc1 (1028);

This is wrong.   malloc functions don't *clobber* anything, AFAIK.
--Dan




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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23382