===================================================================
@@ -266,9 +266,11 @@
immediately above the highest-value value bit. Signed @samp{>>} acts
on negative numbers by sign extension.
-GCC does not use the latitude given in C99 and C11 only to treat certain
-aspects of signed @samp{<<} as undefined, but this is subject to
-change.
+As an extension to the C language, GCC does not use the latitude given in
+C99 and C11 only to treat certain aspects of signed @samp{<<} as undefined.
+However, @option{-fsanitize=shift} (and @option{-fsanitize=undefined}) will
+diagnose such cases. They are also diagnosed where constant
+expressions are required.
@item
@cite{The sign of the remainder on integer division (C90 6.3.5).}
GCC's -fwrapv option does not affect code generation for shifts because currently GCC does not rely on the fact that certain signed shifts trigger undefined behavior. However, the definition of signed arithmetic overflow does extend to shifts; it is only code generation that is limited to addition, subtraction and multiplication. Make the documentation of -fwrapv consistent with the existing text under -fstrict-overflow ("Using '-fwrapv' means that integer signed overflow is fully defined: it wraps."). Ok for trunk, and for GCC 5 branch after 5.3 is released? Paolo * doc/implement-c.texi (Integers Implementation): Make GCC's promises about signed left shift stronger and clarify the cases when they're broken.