* crontab: Add 4.2 branch. Set trunk to 4.3.

[pf3gnuchains/gcc-fork.git] / gcc / cse.c

diff --git a/gcc/cse.c b/gcc/cse.c
index fc15511..0304d6f 100644 (file)
--- a/gcc/cse.c
+++ b/gcc/cse.c
@@ -528,6 +528,10 @@ struct table_elt
 
 static struct table_elt *table[HASH_SIZE];
 
+/* Number of elements in the hash table.  */
+
+static unsigned int table_size;
+
 /* Chain of `struct table_elt's made so far for this function
    but currently removed from the table.  */
 
@@ -961,6 +965,8 @@ new_basic_block (void)
        }
     }
 
+  table_size = 0;
+
 #ifdef HAVE_cc0
   prev_insn = 0;
   prev_insn_cc0 = 0;
@@ -1371,6 +1377,8 @@ remove_from_table (struct table_elt *elt, unsigned int hash)
   /* Now add it to the free element chain.  */
   elt->next_same_hash = free_element_chain;
   free_element_chain = elt;
+
+  table_size--;
 }
 
 /* Look up X in the hash table and return its table element,
@@ -1648,6 +1656,8 @@ insert (rtx x, struct table_elt *classp, unsigned int hash, enum machine_mode mo
        }
     }
 
+  table_size++;
+
   return elt;
 }
 \f
@@ -3432,10 +3442,10 @@ fold_rtx_subreg (rtx x, rtx insn)
   return x;
 }
 
-/* Fold MEM.  */
+/* Fold MEM.  Not to be called directly, see fold_rtx_mem instead.  */
 
 static rtx
-fold_rtx_mem (rtx x, rtx insn)
+fold_rtx_mem_1 (rtx x, rtx insn)
 {
   enum machine_mode mode = GET_MODE (x);
   rtx new;
@@ -3598,6 +3608,51 @@ fold_rtx_mem (rtx x, rtx insn)
   }
 }
 
+/* Fold MEM.  */
+
+static rtx
+fold_rtx_mem (rtx x, rtx insn)
+{
+  /* To avoid infinite oscillations between fold_rtx and fold_rtx_mem,
+     refuse to allow recursion of the latter past n levels.  This can
+     happen because fold_rtx_mem will try to fold the address of the
+     memory reference it is passed, i.e. conceptually throwing away
+     the MEM and reinjecting the bare address into fold_rtx.  As a
+     result, patterns like
+
+       set (reg1)
+          (plus (reg)
+                (mem (plus (reg2) (const_int))))
+
+       set (reg2)
+          (plus (reg)
+                (mem (plus (reg1) (const_int))))
+
+     will defeat any "first-order" short-circuit put in either
+     function to prevent these infinite oscillations.
+
+     The heuristics for determining n is as follows: since each time
+     it is invoked fold_rtx_mem throws away a MEM, and since MEMs
+     are generically not nested, we assume that each invocation of
+     fold_rtx_mem corresponds to a new "top-level" operand, i.e.
+     the source or the destination of a SET.  So fold_rtx_mem is
+     bound to stop or cycle before n recursions, n being the number
+     of expressions recorded in the hash table.  We also leave some
+     play to account for the initial steps.  */
+
+  static unsigned int depth;
+  rtx ret;
+
+  if (depth > 3 + table_size)
+    return x;
+
+  depth++;
+  ret = fold_rtx_mem_1 (x, insn);
+  depth--;
+
+  return ret;
+}
+
 /* If X is a nontrivial arithmetic operation on an argument
    for which a constant value can be determined, return
    the result of operating on that value, as a constant.
@@ -4262,10 +4317,8 @@ fold_rtx (rtx x, rtx insn)
            {
              int is_shift
                = (code == ASHIFT || code == ASHIFTRT || code == LSHIFTRT);
-             rtx y = lookup_as_function (folded_arg0, code);
-             rtx inner_const;
+             rtx y, inner_const, new_const;
              enum rtx_code associate_code;
-             rtx new_const;
 
              if (is_shift
                  && (INTVAL (const_arg1) >= GET_MODE_BITSIZE (mode)
@@ -4278,11 +4331,9 @@ fold_rtx (rtx x, rtx insn)
                    break;
                }
 
+             y = lookup_as_function (folded_arg0, code);
              if (y == 0)
                break;
-             inner_const = equiv_constant (fold_rtx (XEXP (y, 1), 0));
-             if (!inner_const || GET_CODE (inner_const) != CONST_INT)
-               break;
 
              /* If we have compiled a statement like
                 "if (x == (x & mask1))", and now are looking at
@@ -4292,6 +4343,10 @@ fold_rtx (rtx x, rtx insn)
              if (XEXP (y, 0) == folded_arg0)
                break;
 
+             inner_const = equiv_constant (fold_rtx (XEXP (y, 1), 0));
+             if (!inner_const || GET_CODE (inner_const) != CONST_INT)
+               break;
+
              /* Don't associate these operations if they are a PLUS with the
                 same constant and it is a power of two.  These might be doable
                 with a pre- or post-increment.  Similarly for two subtracts of