[RISCV] Add vendor-defined XTheadMemIdx (Indexed Memory Operations) extension

The vendor-defined XTHeadMemIdx (no comparable standard extension exists
at the time of writing) extension adds indexed load/store instructions
as well as load/store and update register instructions.

It is supported by the C9xx cores (e.g., found in the wild in the
Allwinner D1) by Alibaba T-Head.

The current (as of this commit) public documentation for this
extension is available at:
  https://github.com/T-head-Semi/thead-extension-spec/releases/download/2.2.2/xthead-2023-01-30-2.2.2.pdf

Support for these instructions has already landed in GNU Binutils:
  https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=27cfd142d0a7e378d19aa9a1278e2137f849b71b

Depends on D144002

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D144249

1 files changed, 7 insertions, 0 deletions

diff --git a/llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp b/llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp
index e278edc..807d1e9 100644
--- a/llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp
+++ b/llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp
@@ -534,6 +534,13 @@ DecodeStatus RISCVDisassembler::getInstruction(MCInst &MI, uint64_t &Size,
       if (Result != MCDisassembler::Fail)
         return Result;
     }
+    if (STI.hasFeature(RISCV::FeatureVendorXTHeadMemIdx)) {
+      LLVM_DEBUG(dbgs() << "Trying XTHeadMemIdx custom opcode table:\n");
+      Result = decodeInstruction(DecoderTableTHeadMemIdx32, MI, Insn, Address,
+                                 this, STI);
+      if (Result != MCDisassembler::Fail)
+        return Result;
+    }
     if (STI.hasFeature(RISCV::FeatureVendorXTHeadMemPair)) {
       LLVM_DEBUG(dbgs() << "Trying XTHeadMemPair custom opcode table:\n");
       Result = decodeInstruction(DecoderTableTHeadMemPair32, MI, Insn, Address,