* gcc-interface/trans.c (build_binary_op_trapv): Use more efficient

	overflow check for addition/subtraction if neither operand is constant.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@141665 138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/gcc/ada/ChangeLog b/gcc/ada/ChangeLog
index 7db1344..f9d8993 100644 (file)
--- a/gcc/ada/ChangeLog
+++ b/gcc/ada/ChangeLog
@@ -1,3 +1,8 @@
+2008-11-07  Geert Bosch  <bosch@adacore.com>
+
+       * gcc-interface/trans.c (build_binary_op_trapv): Use more efficient
+       overflow check for addition/subtraction if neither operand is constant.
+
 2008-11-06  Eric Botcazou  <ebotcazou@adacore.com>
 
        * gcc-interface/Makefile.in (SPARC/Solaris): Use a common set of

diff --git a/gcc/ada/gcc-interface/trans.c b/gcc/ada/gcc-interface/trans.c
index 9f050bd..5d56ef8 100644 (file)
--- a/gcc/ada/gcc-interface/trans.c
+++ b/gcc/ada/gcc-interface/trans.c
@@ -5998,58 +5998,93 @@ build_binary_op_trapv (enum tree_code code,
   tree gnu_expr;
   tree tmp1, tmp2;
   tree zero = convert (gnu_type, integer_zero_node);
-  tree rhs_ge_zero;
+  tree rhs_lt_zero;
   tree check_pos;
   tree check_neg;
+  tree check;
 
   int precision = TYPE_PRECISION (gnu_type);
 
-  /* Prefer a constant rhs to simplify checks */
+  gcc_assert (!(precision & (precision - 1))); /* ensure power of 2 */
 
-  if (TREE_CONSTANT (lhs) && !TREE_CONSTANT (rhs)
-      && commutative_tree_code (code))
+  /* Prefer a constant or known-positive rhs to simplify checks */
+
+  if (!TREE_CONSTANT (rhs)
+      && commutative_tree_code (code)
+      && (TREE_CONSTANT (lhs) || (!tree_expr_nonnegative_p (rhs)
+                                 && tree_expr_nonnegative_p (lhs))))
     {
-      tree tmp = lhs;
-      lhs = rhs;
-      rhs = tmp;
-   }
+         tree tmp = lhs;
+         lhs = rhs;
+         rhs = tmp;
+    }
+
+  rhs_lt_zero = tree_expr_nonnegative_p (rhs)
+    ? integer_zero_node 
+    : build_binary_op (LT_EXPR, integer_type_node, rhs, zero);
+
+  /* Should use more efficient check for operand_equal_p (lhs, rhs, 0) ??? */
 
-  /* In the case the right-hand size is still not constant, try to
-     use an exact operation in a wider type. */
+  /* Try a few strategies that may be cheaper than the general
+     code at the end of the function, if the RHS is not known.
+     The strategies are:
+       - Call library function for 64-bit multiplication (complex)
+       - Widen, if input arguments are sufficiently small
+       - Determine overflow using wrapped result for addition/subtraction */
 
   if (!TREE_CONSTANT (rhs))
     {
-      int needed_precision = code == MULT_EXPR ? 2 * precision : precision + 1;
+      /* Even for add/subtract double size in order to get another basetype */
+      int needed_precision = precision * 2;
 
       if (code == MULT_EXPR && precision == 64)
        {
          return build_call_2_expr (mulv64_decl, lhs, rhs);
        }
-      else if (needed_precision <= LONG_LONG_TYPE_SIZE)
+      else if (needed_precision <= BITS_PER_WORD
+              || (code == MULT_EXPR 
+                  && needed_precision <= LONG_LONG_TYPE_SIZE))
        {
-         tree calc_type = gnat_type_for_size (needed_precision, 0);
-         tree result;
-         tree check;
+         tree wide_type = gnat_type_for_size (needed_precision, 0);
 
-         result = build_binary_op (code, calc_type,
-                                   convert (calc_type, lhs),
-                                   convert (calc_type, rhs));
+         tree wide_result = build_binary_op (code, wide_type,
+                                             convert (wide_type, lhs),
+                                             convert (wide_type, rhs));
 
-         check = build_binary_op
+         tree check = build_binary_op
            (TRUTH_ORIF_EXPR, integer_type_node,
-            build_binary_op (LT_EXPR, integer_type_node, result,
-                             convert (calc_type, type_min)),
-            build_binary_op (GT_EXPR, integer_type_node, result,
-                             convert (calc_type, type_max)));
+            build_binary_op (LT_EXPR, integer_type_node, wide_result,
+                             convert (wide_type, type_min)),
+            build_binary_op (GT_EXPR, integer_type_node, wide_result,
+                             convert (wide_type, type_max)));
+
+         tree result = convert (gnu_type, wide_result);
 
-         result = convert (gnu_type, result);
 
          return emit_check (check, result, CE_Overflow_Check_Failed);
        }
-    }
+      else if (code == PLUS_EXPR || code == MINUS_EXPR)
+       {
+         tree unsigned_type = gnat_type_for_size (precision, 1);
+         tree wrapped_expr = convert
+           (gnu_type, build_binary_op (code, unsigned_type,
+                                       convert (unsigned_type, lhs),
+                                       convert (unsigned_type, rhs)));
 
-  gnu_expr = build_binary_op (code, gnu_type, lhs, rhs);
-  rhs_ge_zero = build_binary_op (GE_EXPR, integer_type_node, rhs, zero);
+         tree result = convert
+           (gnu_type, build_binary_op (code, gnu_type, lhs, rhs));
+
+         /* Overflow when (rhs < 0) ^ (wrapped_expr < lhs)), for addition
+            or when (rhs < 0) ^ (wrapped_expr > lhs) for subtraction */
+
+         tree check = build_binary_op
+           (TRUTH_XOR_EXPR, integer_type_node, rhs_lt_zero,
+            build_binary_op (code == PLUS_EXPR ? LT_EXPR : GT_EXPR,
+                             integer_type_node, wrapped_expr, lhs));
+
+         return emit_check (check, result, CE_Overflow_Check_Failed);
+       }
+   }
 
   switch (code)
     {
@@ -6079,6 +6114,7 @@ build_binary_op_trapv (enum tree_code code,
 
     case MULT_EXPR:
       /* The check here is designed to be efficient if the rhs is constant,
+         but it will work for any rhs by using integer division.
          Four different check expressions determine wether X * C overflows,
         depending on C.
           C ==  0  =>  false
@@ -6108,9 +6144,12 @@ build_binary_op_trapv (enum tree_code code,
       gcc_unreachable();
     }
 
-  return emit_check (fold_build3 (COND_EXPR, integer_type_node, rhs_ge_zero,
-                                 check_pos, check_neg),
-                    gnu_expr, CE_Overflow_Check_Failed);
+  gnu_expr = build_binary_op (code, gnu_type, lhs, rhs);
+
+  check = fold_build3 (COND_EXPR, integer_type_node,
+                      rhs_lt_zero,  check_neg, check_pos);
+
+  return emit_check (check, gnu_expr, CE_Overflow_Check_Failed);
 }
 
 /* Emit code for a range check. GNU_EXPR is the expression to be checked,