[RFC][PATCH] A change to do_while_loop_p()

[Razya Ladelsky]

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


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;
=