Update comment about BSR.

From-SVN: r13601

gcc/config/sh/sh.md

@@ -29,20 +29,16 @@
 
 ;; ??? Should check all DImode patterns for consistency and usefulness.
 
-;; ??? Should add support for using BSR for short function calls.
-
 ;; ??? The MAC.W and MAC.L instructions are not supported.  There is no
 ;; way to generate them.
 
-;; ??? The BSR instruction is not supported.  It might be possible to
-;; generate it by keeping track of function sizes (and hence relative
-;; addresses), and then using it only if the target is earlier in the same
-;; file, and is within range.  Better would be assembler/linker relaxing,
-;; but that is much harder.
-
 ;; ??? The cmp/str instruction is not supported.  Perhaps it can be used
 ;; for a str* inline function.
 
+;; BSR is not generated by the compiler proper, but when relaxing, it
+;; generates .uses pseudo-ops that allow linker relaxation to create
+;; BSR.  This is actually implemented in bfd/{coff,elf32}-sh.c
+
 ;; Special constraints for SH machine description:
 ;;
 ;;    t -- T