RISC-V: Add T-Head MemIdx vendor extension

T-Head has a range of vendor-specific instructions.
Therefore it makes sense to group them into smaller chunks
in form of vendor extensions.

This patch adds the XTheadMemIdx extension, a collection of T-Head specific
GPR memory access instructions.
The 'th' prefix and the "XTheadMemIdx" extension are documented in a PR
for the RISC-V toolchain conventions ([1]).

In total XTheadCmo introduces the following 44 instructions
(BU,HU,WU only for loads (zero-extend instead of sign-extend)):

* {L,S}{D,W,WU,H,HU,B,BU}{IA,IB} rd, rs1, imm5, imm2
* {L,S}R{D,W,WU,H,HU,B,BU} rd, rs1, rs2, imm2
* {L,S}UR{D,W,WU,H,HU,B,BU} rd, rs1, rs2, imm2

[1] https://github.com/riscv-non-isa/riscv-toolchain-conventions/pull/19

Co-developed-by: Lifang Xia <lifang_xia@linux.alibaba.com>
Signed-off-by: Christoph Müllner <christoph.muellner@vrull.eu>

1 files changed, 5 insertions, 0 deletions

diff --git a/gas/doc/c-riscv.texi b/gas/doc/c-riscv.texi
index 392be0e..ed3d989 100644
--- a/gas/doc/c-riscv.texi
+++ b/gas/doc/c-riscv.texi
@@ -739,6 +739,11 @@ The XTheadMac extension provides multiply-accumulate instructions.
 
 It is documented in @url{https://github.com/T-head-Semi/thead-extension-spec/releases/download/2.0.0/xthead-2022-09-05-2.0.0.pdf}.
 
+@item XTheadMemIdx
+The XTheadMemIdx extension provides GPR memory operations.
+
+It is documented in @url{https://github.com/T-head-Semi/thead-extension-spec/releases/download/2.0.0/xthead-2022-09-05-2.0.0.pdf}.
+
 @item XTheadSync
 The XTheadSync extension provides instructions for multi-processor synchronization.