Fix the handling of edge cases in ARM shifted operands.

This patch fixes load/store instructions to handle less common cases
like "asr #32", "rrx" properly throughout the MC layer.

Patch by Chris Lidbury.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164455 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/ARM/Disassembler/ARMDisassembler.cpp b/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
index 57642e1..bf0dabb 100644
--- a/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
+++ b/lib/Target/ARM/Disassembler/ARMDisassembler.cpp
@@ -1523,6 +1523,8 @@
         return MCDisassembler::Fail;
     }
     unsigned amt = fieldFromInstruction(Insn, 7, 5);
+    if (Opc == ARM_AM::ror && amt == 0)
+      Opc = ARM_AM::rrx;
     unsigned imm = ARM_AM::getAM2Opc(Op, amt, Opc, idx_mode);
 
     Inst.addOperand(MCOperand::CreateImm(imm));
@@ -1564,6 +1566,9 @@
       break;
   }
 
+  if (ShOp == ARM_AM::ror && imm == 0)
+    ShOp = ARM_AM::rrx;
+
   if (!Check(S, DecodeGPRRegisterClass(Inst, Rn, Address, Decoder)))
     return MCDisassembler::Fail;
   if (!Check(S, DecodeGPRRegisterClass(Inst, Rm, Address, Decoder)))