Update 'Q' constraint documentation.

2020-01-06  Michael Meissner  <meissner@linux.ibm.com>

	* config/rs6000/constraints.md (Q constraint): Update
	documentation.
	* doc/md.texi (RS/6000 constraints): Update 'Q' cosntraint
	documentation.

From-SVN: r279939

gcc/config/rs6000/constraints.md

@@ -211,8 +211,7 @@ several times, or that might not access it at all."
        (match_test "GET_RTX_CLASS (GET_CODE (XEXP (op, 0))) != RTX_AUTOINC")))
 
 (define_memory_constraint "Q"
-  "Memory operand that is an offset from a register (it is usually better
-to use @samp{m} or @samp{es} in @code{asm} statements)"
+  "A memory operand addressed by just a base register."
   (and (match_code "mem")
        (match_test "REG_P (XEXP (op, 0))")))
 

gcc/doc/md.texi

@@ -3381,8 +3381,7 @@ allowed when @samp{<} or @samp{>} is used, @samp{es} is basically the same
 as @samp{m} without @samp{<} and @samp{>}.
 
 @item Q
-Memory operand that is an offset from a register (it is usually better
-to use @samp{m} or @samp{es} in @code{asm} statements)
+A memory operand addressed by just a base register.
 
 @item Z
 Memory operand that is an indexed or indirect from a register (it is