* 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
