doc: Document the 'q' constraint for LoongArch

The kernel developers have requested such a constraint to use csrxchg
in inline assembly.

gcc/ChangeLog:

	* doc/md.texi: Document the 'q' constraint for LoongArch.

diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi
index 1a1c1b730897c344fb274dec6337f2d49fe896ad..2a1f9919c5b2f3dab7ee487bf3d556fa50d18d04 100644 (file)
--- a/gcc/doc/md.texi
+++ b/gcc/doc/md.texi
@@ -2918,6 +2918,9 @@ A signed 16-bit constant.
 A memory operand whose address is formed by a base register and offset
 that is suitable for use in instructions with the same addressing mode
 as @code{st.w} and @code{ld.w}.
+@item q
+A general-purpose register except for $r0 and $r1 (for the csrxchg
+instruction)
 @item I
 A signed 12-bit constant (for arithmetic instructions).
 @item K