[ARM] Add an MVE execution domain.

[simon_tatham]

Summary

MVE architecturally specifies a 'beat' system in which a vector
instruction executed now will complete its actual operation over the
next four cycles, so it can overlap with the execution of the previous
and next MVE instruction.

This makes it generally an advantage to avoid moving values back and
forth between MVE registers and anywhere else, if there's any sensible
way to do the same processing in whatever register type the values
already occupied.

That's just what the 'execution domain' system is supposed to achieve.
So here we add a new execution domain which will contain all the MVE
vector instructions when they are added.

[SjoerdMeijer]

looks reasonable

llvm/lib/Target/ARM/ARMInstrFormats.td

class IndexMode<bits<2> val> {
   bits<2> Value = val;
 }
 def IndexModeNone : IndexMode<0>;
 def IndexModePre  : IndexMode<1>;
 def IndexModePost : IndexMode<2>;
 def IndexModeUpd  : IndexMode<3>;
 
 // Instruction execution domain.
-class Domain<bits<3> val> {
-  bits<3> Value = val;
+class Domain<bits<4> val> {
+  bits<4> Value = val;
 }
 def GenericDomain : Domain<0>;
 def VFPDomain     : Domain<1>; // Instructions in VFP domain only
 def NeonDomain    : Domain<2>; // Instructions in Neon domain only
 def VFPNeonDomain : Domain<3>; // Instructions in both VFP & Neon domains
 def VFPNeonA8Domain : Domain<5>; // Instructions in VFP & Neon under A8
+def MVEDomain : Domain<8>; // Instructions in MVE and ARMv8.1m
 
 //===----------------------------------------------------------------------===//
 // ARM special operands.
 //
 
 // ARM imod and iflag operands, used only by the CPS instruction.
 def imod_op : Operand<i32> {
   let PrintMethod = "printCPSIMod";
class InstTemplate<AddrMode am, int sz, IndexMode im,
   let isCodeGenOnly = !eq(!cast<string>(f), "Pseudo");
 
   // The layout of TSFlags should be kept in sync with ARMBaseInfo.h.
   let TSFlags{4-0}   = AM.Value;
   let TSFlags{6-5}   = IndexModeBits;
   let TSFlags{12-7} = Form;
   let TSFlags{13}    = isUnaryDataProc;
   let TSFlags{14}    = canXformTo16Bit;
-  let TSFlags{17-15} = D.Value;
-  let TSFlags{18}    = thumbArithFlagSetting;
+  let TSFlags{18-15} = D.Value;
+  let TSFlags{19}    = thumbArithFlagSetting;
 
   let Constraints = cstr;
   let Itinerary = itin;
 }
 
 class Encoding {
   field bits<32> Inst;
   // Mask of bits that cause an encoding to be UNPREDICTABLE.

llvm/lib/Target/ARM/MCTargetDesc/ARMBaseInfo.h

enum {
     // Xform16Bit - Indicates this Thumb2 instruction may be transformed into
     // a 16-bit Thumb instruction if certain conditions are met.
     Xform16Bit    = 1 << 14,
 
     // ThumbArithFlagSetting - The instruction is a 16-bit flag setting Thumb
     // instruction. Used by the parser to determine whether to require the 'S'
     // suffix on the mnemonic (when not in an IT block) or preclude it (when
     // in an IT block).
-    ThumbArithFlagSetting = 1 << 18,
+    ThumbArithFlagSetting = 1 << 19,
 
     //===------------------------------------------------------------------===//
     // Code domain.
     DomainShift   = 15,
-    DomainMask    = 7 << DomainShift,
+    DomainMask    = 15 << DomainShift,
     DomainGeneral = 0 << DomainShift,
     DomainVFP     = 1 << DomainShift,
     DomainNEON    = 2 << DomainShift,
     DomainNEONA8  = 4 << DomainShift,
+    DomainMVE     = 8 << DomainShift,
 
     //===------------------------------------------------------------------===//
     // Field shifts - such shifts are used to set field while generating
     // machine instructions.
     //
     // FIXME: This list will need adjusting/fixing as the MC code emitter
     // takes shape and the ARMCodeEmitter.cpp bits go away.
     ShiftTypeShift = 4,