SMALL_REGISTER_CLASSES doc fix

[Bernd Schmidt <crux at pool dot informatik dot rwth-aachen dot de>]

The documentation for SMALL_REGISTER_CLASSES no longer matches reality.
(Does a fix like this require a ChangeLog entry?  The GNU coding standards
say no, but the current practice seems to be different).

Bernd

	* tm.texi (SMALL_REGISTER_CLASSES): Make description match reality.

Index: tm.texi
===================================================================
RCS file: /usr/local/cvs/gcs/gcc/tm.texi,v
retrieving revision 1.1.1.36
diff -u -r1.1.1.36 tm.texi
--- tm.texi	1998/11/28 10:28:38	1.1.1.36
+++ tm.texi	1998/11/28 18:50:27
@@ -2022,17 +2022,15 @@
 
 @findex SMALL_REGISTER_CLASSES
 @item SMALL_REGISTER_CLASSES
-Normally the compiler avoids choosing registers that have been
-explicitly mentioned in the rtl as spill registers (these registers are
-normally those used to pass parameters and return values).  However,
-some machines have so few registers of certain classes that there
-would not be enough registers to use as spill registers if this were
-done.
+On some machines, it is risky to let hard registers live across arbitrary
+insns.  Typically, these machines have instructions that require values
+to be in specific registers (like an accumulator), and reload will fail
+if the required hard register is used for another purpose across such an
+insn.
 
 Define @code{SMALL_REGISTER_CLASSES} to be an expression with a non-zero
 value on these machines.  When this macro has a non-zero value, the
-compiler allows registers explicitly used in the rtl to be used as spill
-registers but avoids extending the lifetime of these registers.
+compiler will try to minimize the lifetime of hard registers.
 
 It is always safe to define this macro with a non-zero value, but if you
 unnecessarily define it, you will reduce the amount of optimizations