[ARM] Fix Asm/Disasm of TBB/TBH instructions

Summary:
This fixes Bugzilla #46616 in which it was reported
that "tbb  [pc, r0]" was marked as SoftFail
(aka unpredictable) incorrectly.

Expected behaviour is:
* ARMv8 is required to use sp as rn or rm
  (tbb/tbh only have a Thumb encoding so using Arm mode
  is not an option)
* If rm is the pc then the instruction is always
  unpredictable

Some of this was implemented already and this fixes the
rest. Added tests cover the new and pre-existing handling.

Reviewers: ostannard

Reviewed By: ostannard

Subscribers: kristof.beyls, hiraditya, danielkiss, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D84227

1 files changed, 3 insertions, 1 deletions

diff --git a/llvm/lib/Target/ARM/Disassembler/ARMDisassembler.cpp b/llvm/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
index 54ff0d9..ccef1ba 100644
--- a/llvm/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
+++ b/llvm/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
@@ -4529,12 +4529,14 @@ static DecodeStatus DecodeCoprocessor(MCInst &Inst, unsigned Val,
 static DecodeStatus
 DecodeThumbTableBranch(MCInst &Inst, unsigned Insn,
                        uint64_t Address, const void *Decoder) {
+  const FeatureBitset &FeatureBits =
+    ((const MCDisassembler*)Decoder)->getSubtargetInfo().getFeatureBits();
   DecodeStatus S = MCDisassembler::Success;
 
   unsigned Rn = fieldFromInstruction(Insn, 16, 4);
   unsigned Rm = fieldFromInstruction(Insn, 0, 4);
 
-  if (Rn == ARM::SP) S = MCDisassembler::SoftFail;
+  if (Rn == 13 && !FeatureBits[ARM::HasV8Ops]) S = MCDisassembler::SoftFail;
   if (!Check(S, DecodeGPRRegisterClass(Inst, Rn, Address, Decoder)))
     return MCDisassembler::Fail;
   if (!Check(S, DecoderGPRRegisterClass(Inst, Rm, Address, Decoder)))