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 */