| Message ID | OFF3E28F9B.CAE5BF5B-ONC22579C8.004EFC6A-C22579C8.00524842@il.ibm.com |
|---|---|
| State | New |
| Headers | show |
On Wed, 21 Mar 2012, Razya Ladelsky wrote: > Hi, > > I need to use do_while_loop_p, but I'm not sure its functionality is what > I expected it to be. > > This is the part that I do not understand: > > /* If the header contains just a condition, it is not a do-while loop. */ > stmt = last_and_only_stmt (loop->header); > if (stmt > && gimple_code (stmt) == GIMPLE_COND) > return false; > > The header could contain a condition which is not the loop's exit > condition, > but rather a part of its body, then why do we rule out this loop as a > do_while loop? > > I ran into this in a loop (the outer loop) extracted from bwaves > benchmark: > > do k=1,nz > km1=mod(k+nz-2,nz)+1 > kp1=mod(k,nz)+1 > do j=1,ny > jm1=mod(j+ny-2,ny)+1 > jp1=mod(j,ny)+1 > ..... > enddo > enddo > > which was translated to: > > D.2361_17 = *ny_16(D); > > <bb 5>: > # k_3 = PHI <1(4), k_562(25)> > if (D.2361_17 > 0) > goto <bb 8>; > else > goto <bb 6>; > > <bb 6>: > k_562 = k_3 + 1; > # DEBUG k => k_562 > if (k_3 == D.1583_270) > goto <bb 7>; -------> return > else > goto <bb 25>; > > <bb 25>: > goto <bb 5>; > > <bb 8>: --> starting the body of the the second loop > pretmp.318_776 = (integer(kind=8)) k_3; > pretmp.318_777 = stride.92_20 * pretmp.318_776; > ....... > > > > bb 5 is the header of the outer loop, and bb 25 is the latch. > According to do_while_loop_p () this is NOT a do while loop, but it > seems that it should be. > > I am attaching a patch to change do_while_loop_p() assuming that what I > understand is indeed correct, > Please let me know if I'm right, Not sure what your new tests should do - the patch lacks an update to the comment. Note that this predicate is first of all used in loop header copying to say whether we should avoid copying a header. In this case the condition is not what should prevent copying of the header, but your patch seems to make it so, no? So, please clarify your change. Richard.
Index: tree-ssa-loop-ch.c =================================================================== --- tree-ssa-loop-ch.c (revision 185604) +++ tree-ssa-loop-ch.c (working copy) @@ -107,6 +107,8 @@ should_duplicate_loop_header_p (basic_block header bool do_while_loop_p (struct loop *loop) { + edge exit_edge; + gimple cond_stmt; gimple stmt = last_stmt (loop->latch); /* If the latch of the loop is not empty, it is not a do-while loop. */ @@ -116,8 +118,14 @@ do_while_loop_p (struct loop *loop) /* If the header contains just a condition, it is not a do-while loop. */ stmt = last_and_only_stmt (loop->header); + exit_edge = single_dom_exit (loop); + if (exit_edge) + cond_stmt = last_stmt (exit_edge->src); + else + cond_stmt =stmt; if (stmt - && gimple_code (stmt) == GIMPLE_COND) + && gimple_code (stmt) == GIMPLE_COND + && stmt == cond_stmt) return false; return true;
Hi, I need to use do_while_loop_p, but I'm not sure its functionality is what I expected it to be. This is the part that I do not understand: /* If the header contains just a condition, it is not a do-while loop. */ stmt = last_and_only_stmt (loop->header); if (stmt && gimple_code (stmt) == GIMPLE_COND) return false; The header could contain a condition which is not the loop's exit condition, but rather a part of its body, then why do we rule out this loop as a do_while loop? I ran into this in a loop (the outer loop) extracted from bwaves benchmark: do k=1,nz km1=mod(k+nz-2,nz)+1 kp1=mod(k,nz)+1 do j=1,ny jm1=mod(j+ny-2,ny)+1 jp1=mod(j,ny)+1 ..... enddo enddo which was translated to: D.2361_17 = *ny_16(D); <bb 5>: # k_3 = PHI <1(4), k_562(25)> if (D.2361_17 > 0) goto <bb 8>; else goto <bb 6>; <bb 6>: k_562 = k_3 + 1; # DEBUG k => k_562 if (k_3 == D.1583_270) goto <bb 7>; -------> return else goto <bb 25>; <bb 25>: goto <bb 5>; <bb 8>: --> starting the body of the the second loop pretmp.318_776 = (integer(kind=8)) k_3; pretmp.318_777 = stride.92_20 * pretmp.318_776; ....... bb 5 is the header of the outer loop, and bb 25 is the latch. According to do_while_loop_p () this is NOT a do while loop, but it seems that it should be. I am attaching a patch to change do_while_loop_p() assuming that what I understand is indeed correct, Please let me know if I'm right, Thank you, Razya =