common.opt: Add Wstrict-overflow and Wstrict-overflow=.

./:	* common.opt: Add Wstrict-overflow and Wstrict-overflow=.
	* flags.h (warn_strict_overflow): Declare.
	(enum warn_strict_overflow_code): Define.
	(issue_strict_overflow_warning): New static inline function.
	* opts.c (warn_strict_overflow): New variable.
	(common_handle_option): Handle OPT_Wstrict_overflow and
	OPT_Wstrict_overflow_.
	* c-opts.c (c_common_handle_option): Set warn_strict_overflow for
	OPT_Wall.
	* fold-const.c: Include intl.h.
	(fold_deferring_overflow_warnings): New static variable.
	(fold_deferred_overflow_warning): New static variable.
	(fold_deferred_overflow_code): New static variable.
	(fold_defer_overflow_warnings): New function.
	(fold_undefer_overflow_warnings): New function.
	(fold_undefer_and_ignore_overflow_warnings): New function.
	(fold_deferring_overflow_warnings_p): New function.
	(fold_overflow_warning): New static function.
	(make_range): Add strict_overflow_p parameter.  Change all
	callers.
	(extract_muldiv, extract_muldiv_1): Likewise.
	(fold_unary) [ABS_EXPR]: Check ABS_EXPR before calling
	tree_expr_nonnegative_p.
	(fold_negate_expr): Call fold_overflow_warning.
	(fold_range_test): Likewise.
	(fold_comparison): Likewise.
	(fold_binary): Likewise.  Call tree_expr_nonnegative_warnv_p
	instead of tree_expr_nonnegative_p.
	(tree_expr_nonnegative_warnv_p): Rename from
	tree_expr_nonnegative_p, add strict_overflow_p parameter.
	(tree_expr_nonnegative_p): New function.
	(tree_expr_nonzero_warnv_p): Rename from tree_expr_nonzero_p, add
	strict_overflow_p parameter.
	(tree_expr_nonzero_p): New function.
	* passes.c (verify_interpass_invariants): New static function.
	(execute_one_pass): Call it.
	* tree-ssa-loop-niter.c (expand_simple_operations): Ignore fold
	warnings.
	(number_of_iterations_exit, loop_niter_by_eval): Likewise.
	(estimate_numbers_of_iterations): Likewise.
	(scev_probably_wraps_p): Likewise.
	* tree-ssa-ccp.c: Include "toplev.h".
	(evaluate_stmt): Defer fold overflow warnings until we know we are
	going to optimize.
	(struct fold_stmt_r_data): Add stmt field.
	(fold_stmt_r): Defer fold overflow warnings until we know we
	optimized.
	(fold_stmt): Initialize stmt field of fold_stmt_r_data.
	(fold_stmt_inplace): Likewise.
	* tree-cfgcleanup.c: Include "toplev.h" rather than "errors.h".
	(cleanup_control_expr_graph): Defer fold overflow warnings until
	we know we are going to optimize.
	* tree-cfg.c (fold_cond_expr_cond): Likewise.
	* tree-ssa-threadedge.c (simplify_control_stmt_condition):
	Likewise.
	* tree-vrp.c (vrp_expr_computes_nonnegative): Call
	tree_expr_nonnegative_warnv_p instead of tree_expr_nonnegative_p.
	* tree-ssa-loop-manip.c (create_iv): Likewise.
	* c-typeck.c (build_conditional_expr): Likewise.
	(build_binary_op): Likewise.
	* tree-vrp.c (vrp_expr_computes_nonzero): Call
	tree_expr_nonzero_warnv_p instead of tree_expr_nonzero_p.
	(extract_range_from_unary_expr): Likewise.
	* simplify-rtx.c (simplify_const_relational_operation): Warn when
	assuming that signed overflow does not occur.
	* c-common.c (pointer_int_sum): Ignore fold overflow warnings.
	* tree.h (tree_expr_nonnegative_warnv_p): Declare.
	(fold_defer_overflow_warnings): Declare.
	(fold_undefer_overflow_warnings): Declare.
	(fold_undefer_and_ignore_overflow_warnings): Declare.
	(fold_deferring_overflow_warnings_p): Declare.
	(tree_expr_nonzero_warnv_p): Declare.
	* doc/invoke.texi (Option Summary): Add -Wstrict-overflow to list
	of warning options.
	(Warning Options): Document -Wstrict-overflow.
	* Makefile.in (tree-ssa-threadedge.o): Depend on toplev.h.
	(tree-ssa-ccp.o): Likewise.
	(tree-cfgcleanup.o): Change errors.h dependency to toplev.h.
	(fold-const.o): Depend on intl.h.
testsuite/:
	* gcc.dg/Wstrict-overflow-1.c: New test.
	* gcc.dg/Wstrict-overflow-2.c: New test.
	* gcc.dg/Wstrict-overflow-3.c: New test.
	* gcc.dg/Wstrict-overflow-4.c: New test.
	* gcc.dg/Wstrict-overflow-5.c: New test.
	* gcc.dg/Wstrict-overflow-6.c: New test.
	* gcc.dg/Wstrict-overflow-7.c: New test.
	* gcc.dg/Wstrict-overflow-8.c: New test.
	* gcc.dg/Wstrict-overflow-9.c: New test.
	* gcc.dg/Wstrict-overflow-10.c: New test.

From-SVN: r121895

1 files changed, 45 insertions, 2 deletions

diff --git a/gcc/flags.h b/gcc/flags.h
index 2671ec3..1996bd1 100644
--- a/gcc/flags.h
+++ b/gcc/flags.h
@@ -114,6 +114,11 @@ extern HOST_WIDE_INT larger_than_size;
 
 extern int warn_strict_aliasing;
 
+/* Nonzero means warn about optimizations which rely on undefined
+   signed overflow.  */
+
+extern int warn_strict_overflow;
+
 /* Temporarily suppress certain warnings.
    This is set while reading code from a system header file.  */
 
@@ -289,8 +294,13 @@ extern const char *flag_random_seed;
   (TYPE_UNSIGNED (TYPE) || flag_wrapv)
 
 /* True if overflow is undefined for the given integral type.  We may
-   optimize on the assumption that values in the type never
-   overflow.  */
+   optimize on the assumption that values in the type never overflow.
+
+   IMPORTANT NOTE: Any optimization based on TYPE_OVERFLOW_UNDEFINED
+   must issue a warning based on warn_strict_overflow.  In some cases
+   it will be appropriate to issue the warning immediately, and in
+   other cases it will be appropriate to simply set a flag and let the
+   caller decide whether a warning is appropriate or not.  */
 #define TYPE_OVERFLOW_UNDEFINED(TYPE) \
   (!TYPE_UNSIGNED (TYPE) && !flag_wrapv && !flag_trapv && flag_strict_overflow)
 
@@ -299,4 +309,37 @@ extern const char *flag_random_seed;
 #define TYPE_OVERFLOW_TRAPS(TYPE) \
   (!TYPE_UNSIGNED (TYPE) && flag_trapv)
 
+/* Names for the different levels of -Wstrict-overflow=N.  The numeric
+   values here correspond to N.  */
+
+enum warn_strict_overflow_code
+{
+  /* Overflow warning that should be issued with -Wall: a questionable
+     construct that is easy to avoid even when using macros.  Example:
+     folding (x + CONSTANT > x) to 1.  */
+  WARN_STRICT_OVERFLOW_ALL = 1,
+  /* Overflow warning about folding a comparison to a constant because
+     of undefined signed overflow, other than cases covered by
+     WARN_STRICT_OVERFLOW_ALL.  Example: folding (abs (x) >= 0) to 1
+     (this is false when x == INT_MIN).  */
+  WARN_STRICT_OVERFLOW_CONDITIONAL = 2,
+  /* Overflow warning about changes to comparisons other than folding
+     them to a constant.  Example: folding (x + 1 > 1) to (x > 0).  */
+  WARN_STRICT_OVERFLOW_COMPARISON = 3,
+  /* Overflow warnings not covered by the above cases.  Example:
+     folding ((x * 10) / 5) to (x * 2).  */
+  WARN_STRICT_OVERFLOW_MISC = 4,
+  /* Overflow warnings about reducing magnitude of constants in
+     comparison.  Example: folding (x + 2 > y) to (x + 1 >= y).  */
+  WARN_STRICT_OVERFLOW_MAGNITUDE = 5
+};
+
+/* Whether to emit an overflow warning whose code is C.  */
+
+static inline bool
+issue_strict_overflow_warning (enum warn_strict_overflow_code c)
+{
+  return warn_strict_overflow >= (int) c;
+}
+
 #endif /* ! GCC_FLAGS_H */