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

1 files changed, 6 insertions, 0 deletions

diff --git a/gcc/toplev.c b/gcc/toplev.c
index 7cfb29e..f2c352f 100644
--- a/gcc/toplev.c
+++ b/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.") },
 };