[Bug middle-end/28545] [4.1 Regression] Wrong code for hoisted multiplication

["rguenth at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #10 from rguenth at gcc dot gnu dot org  2006-10-14 11:11 -------
If we watch what happens to the multiplication after VRP, we see that it is
possibly an immediate uses problem:

Hardware watchpoint 6: *(union tree_node **) 3082785444

Old value = (union tree_node *) 0xb7c793dc
New value = (union tree_node *) 0xb7c7971c
set_ssa_use_from_ptr (use=0xb7c7a0bc, val=0xb7c7971c)
    at /home/richard/src/gcc-4_1-branch/gcc/tree-flow-inline.h:330
330       link_imm_use (use, val);

#0  set_ssa_use_from_ptr (use=0xb7c7a0bc, val=0xb7c7971c)
    at /home/richard/src/gcc-4_1-branch/gcc/tree-flow-inline.h:330
#1  0x080d3ed2 in maybe_replace_use (use_p=0xb7c7a0bc)
    at /home/richard/src/gcc-4_1-branch/gcc/tree-into-ssa.c:1386
#2  0x080d3d05 in rewrite_update_stmt (walk_data=0xbfaa5f50, bb=0xb7bfa460, si=
      {tsi = {ptr = 0xb7bf8f78, container = 0xb7c78018}, bb = 0xb7bfa460})
    at /home/richard/src/gcc-4_1-branch/gcc/tree-into-ssa.c:1465
#3  0x080f1573 in walk_dominator_tree (walk_data=0xbfaa5f50, bb=0xb7bfa460)
    at /home/richard/src/gcc-4_1-branch/gcc/domwalk.c:196
#4  0x080f1616 in walk_dominator_tree (walk_data=0xbfaa5f50, bb=0xb7bfa410)
    at /home/richard/src/gcc-4_1-branch/gcc/domwalk.c:212
#5  0x080f1616 in walk_dominator_tree (walk_data=0xbfaa5f50, bb=0xb7bfa5f0)
    at /home/richard/src/gcc-4_1-branch/gcc/domwalk.c:212
#6  0x080f1616 in walk_dominator_tree (walk_data=0xbfaa5f50, bb=0xb7bfa4b0)
    at /home/richard/src/gcc-4_1-branch/gcc/domwalk.c:212
#7  0x080f1616 in walk_dominator_tree (walk_data=0xbfaa5f50, bb=0xb7bfa640)
    at /home/richard/src/gcc-4_1-branch/gcc/domwalk.c:212
#8  0x080f1616 in walk_dominator_tree (walk_data=0xbfaa5f50, bb=0xb7bfa550)
    at /home/richard/src/gcc-4_1-branch/gcc/domwalk.c:212
#9  0x080d42c4 in rewrite_blocks (entry=0xb7bfa550, what=REWRITE_UPDATE,
    blocks=0x86ab0d8)
    at /home/richard/src/gcc-4_1-branch/gcc/tree-into-ssa.c:1616
#10 0x080d6d10 in update_ssa (update_flags=256)
    at /home/richard/src/gcc-4_1-branch/gcc/tree-into-ssa.c:2798
#11 0x08403f38 in insert_range_assertions ()
    at /home/richard/src/gcc-4_1-branch/gcc/tree-vrp.c:2960
#12 0x08406ce7 in execute_vrp ()
    at /home/richard/src/gcc-4_1-branch/gcc/tree-vrp.c:4176

it changes a few times until finally it settles at the wrong solution.

It get's magically fixed if I disable swapping tree operands in 
get_expr_operands ()  (WTF!?)  -  so this seems to be an operand-scanner
vs. update_ssa interaction?

Index: tree-ssa-operands.c
===================================================================
*** tree-ssa-operands.c (revision 117726)
--- tree-ssa-operands.c (working copy)
*************** get_expr_operands (tree stmt, tree *expr
*** 1257,1295 ****
      case ASSERT_EXPR:
      do_binary:
        {
-       tree op0 = TREE_OPERAND (expr, 0);
-       tree op1 = TREE_OPERAND (expr, 1);
-
-       /* If it would be profitable to swap the operands, then do so to
-          canonicalize the statement, enabling better optimization.
-
-          By placing canonicalization of such expressions here we
-          transparently keep statements in canonical form, even
-          when the statement is modified.  */
-       if (tree_swap_operands_p (op0, op1, false))
-         {
-           /* For relationals we need to swap the operands
-              and change the code.  */
-           if (code == LT_EXPR
-               || code == GT_EXPR
-               || code == LE_EXPR
-               || code == GE_EXPR)
-             {
-               TREE_SET_CODE (expr, swap_tree_comparison (code));
-               swap_tree_operands (stmt,
-                                   &TREE_OPERAND (expr, 0),
-                                   &TREE_OPERAND (expr, 1));
-             }
-
-           /* For a commutative operator we can just swap the operands.  */
-           else if (commutative_tree_code (code))
-             {
-               swap_tree_operands (stmt,
-                                   &TREE_OPERAND (expr, 0),
-                                   &TREE_OPERAND (expr, 1));
-             }
-         }
-
        get_expr_operands (stmt, &TREE_OPERAND (expr, 0), flags);
        get_expr_operands (stmt, &TREE_OPERAND (expr, 1), flags);
        return;
--- 1257,1262 ----


note this patch seems to be in mainline already!?  My archology skills are
not good enough to figure out when it was gone.


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |amacleod at redhat dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28545