flags.h (flag_wrapv): New flag controlling overflow semantics.

* flags.h (flag_wrapv): New flag controlling overflow semantics.
	* toplev.c (flag_wrapv): Declare the variable with default false.
	(lang_independent_options): New option "-fwrapv" to set the above.

	* fold-const.c (extract_muldiv_1): Disable optimization of (2*x)/2
	as x, when signed arithmetic overflow wraps around.
	(fold): Optimize "-A - B" as "-B - A" if overflow wraps around.
	* loop.c (basic_induction_var): Ignore BIVs that rely on undefined
	overflow when flag_wrapv is true.

	* java/lang.c (java_init_options): Prescribe wrap-around two's
	complement arithmetic overflow by setting flag_wrapv.

	* doc/invoke.texi: Document new -fwrapv command line option.
	* doc/c-tree.texi: Mention that the overflow semantics of
	NEGATE_EXPR, PLUS_EXPR, MINUS_EXPR and MULT_EXPR is dependent
	upon both flag_wrapv and flag_trapv.

	* gcc.dg/fwrapv-1.c: New test case.
	* gcc.dg/fwrapv-2.c: New test case.

	* libjava.lang/Overflow.java: New test.
	* libjava.lang/Overflow.out: New file.

From-SVN: r67270

gcc/ChangeLog

@@ -1,3 +1,20 @@
+2003-05-31  Roger Sayle  <roger@eyesopen.com>
+
+	* flags.h (flag_wrapv): New flag controlling overflow semantics.
+	* toplev.c (flag_wrapv): Declare the variable with default false.
+	(lang_independent_options): New option "-fwrapv" to set the above.
+
+	* fold-const.c (extract_muldiv_1): Disable optimization of (2*x)/2 
+	as x, when signed arithmetic overflow wraps around.
+	(fold): Optimize "-A - B" as "-B - A" if overflow wraps around.
+	* loop.c (basic_induction_var): Ignore BIVs that rely on undefined
+	overflow when flag_wrapv is true.
+
+	* doc/invoke.texi: Document new -fwrapv command line option.
+	* doc/c-tree.texi: Mention that the overflow semantics of
+	NEGATE_EXPR, PLUS_EXPR, MINUS_EXPR and MULT_EXPR is dependent
+	upon both flag_wrapv and flag_trapv.
+
 2003-05-31  Eric Botcazou  <ebotcazou@libertysurf.fr>
 
 	* doc/install.texi (mips-sgi-irix5): Add missing

gcc/doc/c-tree.texi

@@ -1914,6 +1914,9 @@ These nodes represent unary negation of the single operand, for both
 integer and floating-point types.  The type of negation can be
 determined by looking at the type of the expression.
 
+The behavior of this operation on signed arithmetic overflow is
+controlled by the @code{flag_wrapv} and @code{flag_trapv} variables.
+
 @item BIT_NOT_EXPR
 These nodes represent bitwise complement, and will always have integral
 type.  The only operand is the value to be complemented.
@@ -2067,6 +2070,9 @@ The @code{TRUNC_MOD_EXPR} of two operands @code{a} and @code{b} is
 always @code{a - (a/b)*b} where the division is as if computed by a
 @code{TRUNC_DIV_EXPR}.
 
+The behavior of these operations on signed arithmetic overflow is
+controlled by the @code{flag_wrapv} and @code{flag_trapv} variables.
+
 @item ARRAY_REF
 These nodes represent array accesses.  The first operand is the array;
 the second is the index.  To calculate the address of the memory

gcc/doc/invoke.texi

@@ -680,7 +680,7 @@ in the following sections.
 -fargument-alias  -fargument-noalias @gol
 -fargument-noalias-global  -fleading-underscore @gol
 -ftls-model=@var{model} @gol
--ftrapv  -fbounds-check}
+-ftrapv  -fwrapv  -fbounds-check}
 @end table
 
 @menu
@@ -10850,6 +10850,14 @@ this option defaults to true and false respectively.
 This option generates traps for signed overflow on addition, subtraction,
 multiplication operations.
 
+@item -fwrapv
+@opindex fwrapv
+This option instructs the compiler to assume that signed arithmetic
+overflow of addition, subtraction and multiplication wraps around
+using twos-complement representation.  This flag enables some optimzations
+and disables other.  This option is enabled by default for the Java
+front-end, as required by the Java language specification.
+
 @item -fexceptions
 @opindex fexceptions
 Enable exception handling.  Generates extra code needed to propagate

gcc/flags.h

@@ -585,6 +585,9 @@ extern int frame_pointer_needed;
    for PLUS / SUB / MULT.  */
 extern int flag_trapv;
 
+/* Nonzero if the signed arithmetic overflow should wrap around.  */
+extern int flag_wrapv;
+
 /* Value of the -G xx switch, and whether it was passed or not.  */
 extern unsigned HOST_WIDE_INT g_switch_value;
 extern int g_switch_set;

gcc/fold-const.c

@@ -4381,6 +4381,7 @@ extract_muldiv_1 (t, c, code, wide_type)
 	 overflowed.  */
       if ((! TREE_UNSIGNED (ctype)
 	   || (TREE_CODE (ctype) == INTEGER_TYPE && TYPE_IS_SIZETYPE (ctype)))
+	  && ! flag_wrapv
 	  && ((code == MULT_EXPR && tcode == EXACT_DIV_EXPR)
 	      || (tcode == MULT_EXPR
 		  && code != TRUNC_MOD_EXPR && code != CEIL_MOD_EXPR
@@ -5765,7 +5766,8 @@ fold (expr)
 	return fold (build (PLUS_EXPR, type, arg0, TREE_OPERAND (arg1, 0)));
       /* (-A) - B -> (-B) - A  where B is easily negated and we can swap.  */
       if (TREE_CODE (arg0) == NEGATE_EXPR
-	  && FLOAT_TYPE_P (type)
+	  && (FLOAT_TYPE_P (type)
+	      || (INTEGRAL_TYPE_P (type) && flag_wrapv && !flag_trapv))
 	  && negate_expr_p (arg1)
 	  && (! TREE_SIDE_EFFECTS (arg0) || TREE_CONSTANT (arg1))
 	  && (! TREE_SIDE_EFFECTS (arg1) || TREE_CONSTANT (arg0)))

gcc/java/ChangeLog

@@ -1,3 +1,8 @@
+2003-05-31  Roger Sayle  <roger@eyesopen.com>
+
+	* lang.c (java_init_options): Prescribe wrap-around two's
+	complement arithmetic overflow by setting flag_wrapv.
+
 2003-05-29  Roger Sayle  <roger@eyesopen.com>
 
 	* builtins.c (cos_builtin, sin_builtin, sqrt_builtin): Delete.

gcc/java/lang.c

@@ -740,6 +740,9 @@ java_init_options (void)
 
   /* In Java floating point operations never trap.  */
   flag_trapping_math = 0;
+
+  /* In Java arithmetic overflow always wraps around.  */
+  flag_wrapv = 1;
 }
 
 static bool

gcc/loop.c

@@ -6462,6 +6462,9 @@ basic_induction_var (loop, x, mode, dest_reg, p, inc_val, mult_val, location)
 	return 0;
 
     case SIGN_EXTEND:
+      /* Ignore this BIV if signed arithmetic overflow is defined.  */
+      if (flag_wrapv)
+	return 0;
       return basic_induction_var (loop, XEXP (x, 0), GET_MODE (XEXP (x, 0)),
 				  dest_reg, p, inc_val, mult_val, location);
 

gcc/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2003-05-31  Roger Sayle  <roger@eyesopen.com>
+
+	* gcc.dg/fwrapv-1.c: New test case.
+	* gcc.dg/fwrapv-2.c: New test case.
+
 2003-05-31  Kriang Lerdsuwanakij  <lerdsuwa@users.sourceforge.net>
 
 	PR c++/10956

gcc/testsuite/gcc.dg/fwrapv-1.c

@@ -0,0 +1,28 @@
+/* Copyright (C) 2003 Free Software Foundation.
+
+   Test that the -fwrapv command line option is accepted and disables
+   "unsafe" optimizations that rely on undefined arithmetic overflow.
+
+   Written by Roger Sayle, 24th March 2003.  */
+
+/* { dg-do run } */
+/* { dg-options "-O2 -fwrapv" } */
+
+#include <limits.h>
+
+extern void abort ();
+
+int test(int x)
+{
+  return (2*x)/2;
+}
+
+main()
+{
+  int x = INT_MAX;
+
+  if (test(x) == x)
+    abort ();
+  return 0;
+}
+

gcc/testsuite/gcc.dg/fwrapv-2.c

@@ -0,0 +1,28 @@
+/* Copyright (C) 2003 Free Software Foundation.
+
+   Test that the -fno-wrapv command line option is accepted and enables
+   "unsafe" optimizations that rely on undefined arithmetic overflow.
+
+   Written by Roger Sayle, 31st May 2003.  */
+
+/* { dg-do run } */
+/* { dg-options "-O2 -fno-wrapv" } */
+
+#include <limits.h>
+
+extern void abort ();
+
+int test(int x)
+{
+  return (2*x)/2;
+}
+
+main()
+{
+  int x = INT_MAX;
+
+  if (test(x) != x)
+    abort ();
+  return 0;
+}
+

gcc/toplev.c

@@ -977,8 +977,12 @@ typedef struct
 }
 lang_independent_options;
 
+/* Nonzero if signed arithmetic overflow should trap.  */
 int flag_trapv = 0;
 
+/* Nonzero if signed arithmetic overflow should wrap around.  */
+int flag_wrapv = 0;
+
 /* Add or remove a leading underscore from user symbols.  */
 int flag_leading_underscore = -1;
 
@@ -1220,6 +1224,8 @@ static const lang_independent_options f_options[] =
    N_("Report on permanent memory allocation at end of run") },
   { "trapv", &flag_trapv, 1,
    N_("Trap for signed overflow in addition / subtraction / multiplication") },
+  { "wrapv", &flag_wrapv, 1,
+   N_("Assume signed arithmetic overflow wraps around") },
   { "new-ra", &flag_new_regalloc, 1,
    N_("Use graph coloring register allocation.") },
 };

libjava/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2003-05-31  Roger Sayle  <roger@eyesopen.com>
+
+	* libjava.lang/Overflow.java: New test.
+	* libjava.lang/Overflow.out: New file.
+
 2003-05-06  Tom Tromey  <tromey@redhat.com>
 
 	* libjava.lang/verify.java: New file.

libjava/testsuite/libjava.lang/Overflow.java

@@ -0,0 +1,16 @@
+class Overflow
+{
+  static int test(int x)
+  {
+    return (2*x)/2;
+  }
+
+  public static void main(String argv[])
+  {
+    int x = Integer.MAX_VALUE;
+
+    if (test(x) == x)
+      throw new RuntimeException ();
+  }
+}
+