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, 3 insertions, 0 deletions

diff --git a/gcc/loop.c b/gcc/loop.c
index e5ae479..737ec89 100644
--- a/gcc/loop.c
+++ b/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);