[mips][microMIPS] Implement LWXS instruction

[jkolek]

Summary

Implement 32-bit microMIPS instruction LWXS.

[sstankovic]

LGTM

[jkolek]

Closed by commit rL222348 (authored by @jkolek).

lib/Target/Mips/MicroMipsInstrFormats.td

   let Inst{15-6}  = op;
   let Inst{5-0}   = 0x3c;
 }
+
+class LWXS_FM_MM<bits<10> funct> {
+  bits<5> rd;
+  bits<5> base;
+  bits<5> index;
+
+  bits<32> Inst;
+
+  let Inst{31-26} = 0x0;
+  let Inst{25-21} = index;
+  let Inst{20-16} = base;
+  let Inst{15-11} = rd;
+  let Inst{10}    = 0;
+  let Inst{9-0}   = funct;
+}

lib/Target/Mips/MicroMipsInstrInfo.td

            !strconcat(opstr, "\t$rs, $offset"), [], IIBranch, FrmI, opstr>;
 }
 
+class LoadWordIndexedScaledMM<string opstr, RegisterOperand RO,
+                              InstrItinClass Itin = NoItinerary,
+                              SDPatternOperator OpNode = null_frag> :
+  InstSE<(outs RO:$rd), (ins PtrRC:$base, PtrRC:$index),
+         !strconcat(opstr, "\t$rd, ${index}(${base})"), [], Itin, FrmFI>;
+
 def ADDU16_MM : ArithRMM16<"addu16", GPRMM16Opnd, 1, II_ADDU, add>,
                 ARITH_FM_MM16<0>;
 def SUBU16_MM : ArithRMM16<"subu16", GPRMM16Opnd, 0, II_SUBU, sub>,

     def SW_MM  : Store<"sw", GPR32Opnd>, MMRel, LW_FM_MM<0x3e>;
   }
 
+  def LWXS_MM : LoadWordIndexedScaledMM<"lwxs", GPR32Opnd>, LWXS_FM_MM<0x118>;
+
   def LWU_MM : LoadMM<"lwu", GPR32Opnd, zextloadi32, II_LWU>, LL_FM_MM<0xe>;
 
   /// Load and Store Instructions - unaligned

test/MC/Mips/micromips-loadstore-instructions.s

 # CHECK-EL: ll     $2, 8($4)      # encoding: [0x44,0x60,0x08,0x30]
 # CHECK-EL: sc     $2, 8($4)      # encoding: [0x44,0x60,0x08,0xb0]
 # CHECK-EL: lwu    $2, 8($4)      # encoding: [0x44,0x60,0x08,0xe0]
+# CHECK-EL: lwxs   $2, $3($4)     # encoding: [0x64,0x00,0x18,0x11]
 #------------------------------------------------------------------------------
 # Big endian
 #------------------------------------------------------------------------------

 # CHECK-EB: ll     $2, 8($4)      # encoding: [0x60,0x44,0x30,0x08]
 # CHECK-EB: sc     $2, 8($4)      # encoding: [0x60,0x44,0xb0,0x08]
 # CHECK-EB: lwu    $2, 8($4)      # encoding: [0x60,0x44,0xe0,0x08]
+# CHECK-EB: lwxs   $2, $3($4)     # encoding: [0x00,0x64,0x11,0x18]
      lb     $5, 8($4)
      lbu    $6, 8($4)
      lh     $2, 8($4)

      ll     $2, 8($4)
      sc     $2, 8($4)
      lwu    $2, 8($4)
+     lwxs   $2, $3($4)