ARM ISB instruction assembly parsing.

The ISB instruction takes an optional operand, just like DMB/DSB. Typically
only 'sy' is meaningful.

llvm-svn: 135156
diff --git a/llvm/lib/Target/ARM/ARMInstrInfo.td b/llvm/lib/Target/ARM/ARMInstrInfo.td
index 5d646e7..7e5d136 100644
--- a/llvm/lib/Target/ARM/ARMInstrInfo.td
+++ b/llvm/lib/Target/ARM/ARMInstrInfo.td
@@ -3317,12 +3317,16 @@
 def : InstAlias<"dsb", (DSB 0xf)>, Requires<[IsARM, HasDB]>;
 
 // ISB has only full system option
-def ISB : AInoP<(outs), (ins), MiscFrm, NoItinerary, "isb", "", []>,
+def ISB : AInoP<(outs), (ins memb_opt:$opt), MiscFrm, NoItinerary,
+                "isb", "\t$opt", []>,
                 Requires<[IsARM, HasDB]> {
+  bits<4> opt;
   let Inst{31-4} = 0xf57ff06;
-  let Inst{3-0} = 0b1111;
+  let Inst{3-0} = opt;
 }
 
+def : InstAlias<"isb", (ISB 0xf)>, Requires<[IsARM, HasDB]>;
+
 let usesCustomInserter = 1 in {
   let Uses = [CPSR] in {
     def ATOMIC_LOAD_ADD_I8 : PseudoInst<