[PATCH] PR 20994

[Devang Patel <dpatel at apple dot com>]

This is the case when tree if-conversion produces

    x = ! (a == b) : p , q;

This patch fixes tree if-convertor so that it produces

    x = (a == b) : q , p ;

This is preferable over
    t1 = (a == b);
    x = !t1 : p : q;
, hence this song-and-dance.

       * tree-if-conv.c (find_phi_replacement_condition): Avoid
        generating x = !(a == b) : p : q;.
        (pass_if_conversion): Verify stmts and flow.

        * gcc.dg/tree-ssa/ifc-3.c: New test.

Bootstrapped and tested on powerpc-darwin.
OK for mainline ?

Thanks,
-
Devang

[Patch is small so I am including it here instead of attaching
 diff file. ]

Index: tree-if-conv.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/tree-if-conv.c,v
retrieving revision 2.37
diff -Idpatel.pbxuser -c -3 -p -r2.37 tree-if-conv.c
*** tree-if-conv.c      13 Apr 2005 19:02:31 -0000      2.37
--- tree-if-conv.c      19 Apr 2005 18:02:46 -0000
*************** find_phi_replacement_condition (struct l
*** 665,710 ****
                                basic_block bb, tree *cond,
                                  block_stmt_iterator *bsi)
  {
!   edge e;
!   basic_block p1 = NULL;
!   basic_block p2 = NULL;
!   basic_block true_bb = NULL;
    tree tmp_cond;
-   edge_iterator ei;

!   FOR_EACH_EDGE (e, ei, bb->preds)
!     {
!       if (p1 == NULL)
!       p1 = e->src;
!       else
!       {
!         gcc_assert (!p2);
!         p2 = e->src;
!       }
!     }

!   /* Use condition that is not TRUTH_NOT_EXPR in conditional modify  
expr.  */
!   tmp_cond = p1->aux;
    if (TREE_CODE (tmp_cond) == TRUTH_NOT_EXPR)
      {
!       /* If p2 is loop->header than its aux field does not have useful
!        info. Instead use !(cond) where cond is p1's aux field.  */
!       if (p2 == loop->header)
!       *cond = invert_truthvalue (unshare_expr (p1->aux));
!       else
!       *cond  = p2->aux;
!       true_bb = p2;
      }
!   else
      {
!       /* If p1 is loop->header than its aux field does not have useful
!        info. Instead use !(cond) where cond is p2's aux field.  */
!       if (p1 == loop->header)
!       *cond = invert_truthvalue (unshare_expr (p2->aux));
        else
!       *cond  = p1->aux;
!       true_bb = p1;
      }

    /* Create temp. for the condition. Vectorizer prefers to have  
gimple
       value as condition. Various targets use different means to  
communicate
--- 665,728 ----
                                basic_block bb, tree *cond,
                                  block_stmt_iterator *bsi)
  {
!   basic_block first_bb = NULL;
!   basic_block second_bb = NULL;
    tree tmp_cond;

!   gcc_assert (EDGE_COUNT (bb->preds) == 2);
!   first_bb = (EDGE_PRED (bb, 0))->src;
!   second_bb = (EDGE_PRED (bb, 1))->src;

!   /* Use condition based on following criteria:
!      1)
!        S1: x = !c ? a : b;
!
!        S2: x = c ? b : a;
!
!        S2 is preferred over S1. Make 'b' first_bb and use its  
condition.
!
!      2) Do not make loop header first_bb.
!
!      3)
!        S1: x = !(c == d)? a : b;
!
!        S21: t1 = c == d;
!        S22: x = t1 ? b : a;
!
!        S3: x = (c == d) ? b : a;
!
!        S3 is preferred over S1 and S2*, Make 'b' first_bb and use
!        its condition.  */
!
!   /* Select condition that is not TRUTH_NOT_EXPR.  */
!   tmp_cond = first_bb->aux;
    if (TREE_CODE (tmp_cond) == TRUTH_NOT_EXPR)
      {
!       basic_block tmp_bb;
!       tmp_bb = first_bb;
!       first_bb = second_bb;
!       second_bb = first_bb;
      }
!
!   /* Check if first_bb is loop header or not.  */
!   if (first_bb == loop->header)
      {
!       tmp_cond = second_bb->aux;
!       if (TREE_CODE (tmp_cond) == TRUTH_NOT_EXPR)
!       {
!         /* Select non loop header condition but do not swith bb.  */
!         *cond = invert_truthvalue (unshare_expr (tmp_cond));
!       }
        else
!       {
!         /* Select non loop header condition.  */
!         first_bb = second_bb;
!         *cond = first_bb->aux;
!       }
      }
+   else
+     /* first_bb is not loop header */
+     *cond = first_bb->aux;

    /* Create temp. for the condition. Vectorizer prefers to have  
gimple
       value as condition. Various targets use different means to  
communicate
*************** find_phi_replacement_condition (struct l
*** 722,728 ****

    gcc_assert (*cond);

!   return true_bb;
  }


--- 740,746 ----

    gcc_assert (*cond);

!   return first_bb;
  }


*************** struct tree_opt_pass pass_if_conversion
*** 1119,1124 ****
    0,                                  /* properties_provided */
    0,                                  /* properties_destroyed */
    0,                                  /* todo_flags_start */
!   TODO_dump_func | TODO_verify_loops, /* todo_flags_finish */
    0                                   /* letter */
  };
--- 1137,1143 ----
    0,                                  /* properties_provided */
    0,                                  /* properties_destroyed */
    0,                                  /* todo_flags_start */
!   TODO_dump_func | TODO_verify_loops | TODO_verify_stmts |  
TODO_verify_flow,
!                                         /* todo_flags_finish */
    0                                   /* letter */
  };
Index: testsuite/gcc.dg/tree-ssa/ifc-3.c
===================================================================
RCS file: testsuite/gcc.dg/tree-ssa/ifc-3.c
diff -N testsuite/gcc.dg/tree-ssa/ifc-3.c
*** /dev/null   1 Jan 1970 00:00:00 -0000
--- testsuite/gcc.dg/tree-ssa/ifc-3.c   19 Apr 2005 18:02:49 -0000
***************
*** 0 ****
--- 1,12 ----
+ /* PR 20994 */
+ /* { dg-do compile } */
+ int foo(double* p, double* q)
+ {
+     int i=0;
+
+     for (; q!=p; ++q)
+         if (*q)
+             ++i;
+
+     return i;
+ }