* doc/extend.texi (Hints implementation): Document that GCC

	mostly ignores `register'.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@55890 138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 01fd54a..311566b 100644 (file)
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2002-07-30  Geoffrey Keating  <geoffk@redhat.com>
+
+       * doc/extend.texi (Hints implementation): Document that GCC
+       mostly ignores `register'.
+
 2002-07-30  Toon Moene  <toon@moene.indiv.nluug.nl>
 
        * flags.h: Declare flag_finite_math_only.

diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 6fdf7ff..0ddcb34 100644 (file)
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -248,6 +248,27 @@ of the same array (6.5.6).}
 @cite{The extent to which suggestions made by using the @code{register}
 storage-class specifier are effective (6.7.1).}
 
+The @code{register} specifier affects code generation only in these ways:
+
+@itemize @bullet
+@item
+When used as part of the register variable extension, see 
+@ref{Explicit Reg Vars}.
+
+@item
+When @option{-O0} is in use, the compiler allocates distinct stack
+memory for all variables that do not have the @code{register}
+storage-class specifier; if @code{register} is specified, the variable
+may have a shorter lifespan than the code would indicate and may never
+be placed in memory.
+
+@item
+On some rare x86 targets, @code{setjmp} doesn't save the registers in
+all circumstances.  In those cases, GCC doesn't allocate any variables
+in registers unless they are marked @code{register}.
+
+@end itemize
+
 @item
 @cite{The extent to which suggestions made by using the inline function
 specifier are effective (6.7.4).}