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question about optimization and integer truncation
- From: Emese Revfy <re dot emese at gmail dot com>
- To: gcc-help at gcc dot gnu dot org
- Date: Sun, 16 Oct 2011 21:51:33 +0200
- Subject: question about optimization and integer truncation
Hi,
I have a question regarding where certain optimization takes place. Given the following code:
235 u32 string_area_size;
237 u32 cid_list_size;
239 u32 count;
...
294 cid_list_size = sizeof(struct acpica_device_id_list) +
295 ((count - 1) * sizeof(struct acpica_device_id)) + string_area_size;
I get the following ssa representation:
D.27638_41 = count_7 + 268435455;
D.27639_42 = D.27638_41 * 16;
D.27640_43 = D.27639_42 + string_area_size_4;
cid_list_size_44 = D.27640_43 + 24;
D.27641_45 = (acpi_size) cid_list_size_44;
As you can see, the computation of (count - 1) * sizeof(...) is based on unsigned integer truncation.
Can you tell me where exactly in gcc this optimization happens? (which file/function)
Thanks,
Emese