On Fri, Apr 18, 2008 at 9:34 AM, Sandeep Maram <[EMAIL PROTECTED]> wrote:
> Hi,
>
> Consider the 2 for loops given below.
>
> for (i = 0; i < N ; i++)
> {
> a[i]= 1;
> }
>
> for (i = 0; i < N ; i++)
> {
> j = j+a[i];
> }
>
> The headers of these 2 loops are bb_3, bb_6 respectively. They are as
> follows.
>
> bb_3 (preds = {bb_4 bb_2 }, succs = {bb_4 bb_5 })
> {
> <bb 3>:
> # a_27 = PHI <a_18(4), a_17(D)(2)>
> # i_24 = PHI <i_7(4), 0(2)>
> # a_18 = VDEF <a_27> { a }
> a[i_24] = 1;
> i_7 = i_24 + 1;
> if (i_7 <= 999)
> goto <bb 4>;
> else
> goto <bb 5>;
>
> }
>
> bb_6 (preds = {bb_5 bb_7 }, succs = {bb_7 bb_8 })
> {
> <bb 6>:
> # j_26 = PHI <0(5), j_12(7)>
> # i_25 = PHI <0(5), i_13(7)>
> # VUSE <a_18> { a }
>
> D.1189_10 = a[i_25];
> D.1190_11 = (unsigned int) D.1189_10;
> j_12 = D.1190_11 + j_26;
> i_13 = i_25 + 1;
> if (i_13 <= 999)
> goto <bb 7>;
> else
> goto <bb 8>;
>
> }
>
> I am transfering statements from bb_6 to bb_3 using code -
>
> for (bsi = bsi_start (loop_a->header); !bsi_end_p (bsi);)
> {
> if ((TREE_CODE (bsi_stmt (bsi)) != LABEL_EXPR) && (TREE_CODE
> (bsi_stmt (bsi)) != COND_EXPR))
> {
> bsi_move_before (&bsi, &bsi_b_last);
> }
> else
> {
> bsi_next (&bsi);
> }
> }
>
> After this the two BBs look like -
>
> bb_6 (preds = {bb_5 bb_7 }, succs = {bb_7 bb_8 })
> {
> <bb 6>:
> # j_26 = PHI <0(5), j_12(7)>
> # i_25 = PHI <0(5), i_13(7)>
> if (i_13 <= 999)
> goto <bb 7>;
> else
> goto <bb 8>;
>
> }
>
> bb_3 (preds = {bb_4 bb_2 }, succs = {bb_4 bb_5 })
> {
> <bb 3>:
> # a_27 = PHI <a_18(4), a_17(D)(2)>
> # i_24 = PHI <i_7(4), 0(2)>
> # a_18 = VDEF <a_27> { a }
> a[i_24] = 1;
> # VUSE <a_18> { a }
>
> D.1189_10 = a[i_25];
> D.1190_11 = (unsigned int) D.1189_10;
> j_12 = D.1190_11 + j_26;
> i_13 = i_25 + 1;
> i_7 = i_24 + 1;
> if (i_7 <= 999)
> goto <bb 4>;
> else
> goto <bb 5>;
>
> }
>
> The iterator variables for the 2 loops are i_24, i_25 respectively. So
> when the statements are transferred, there is a problem with i_25 in
> bb_3 . How can I change the name of i_25 to i_24 ?
You can for example add a copy instruction
i_25 = i_24
at the top of the new loop (but you have to remove the existing definition
for i_25 in the old loop then). Otherwise you can change and walk
operands of trees using the immediate use iterators and SET_USE.
Just grep for it and you'll find example uses.
Richard.
