s390: introduce DUMY opcode for special use.

BUG=

R=joransiu@ca.ibm.com, michael_dawson@ca.ibm.com, bjaideep@ca.ibm.com

Review-Url: https://codereview.chromium.org/2522283003
Cr-Commit-Position: refs/heads/master@{#41238}

src/s390/assembler-s390.cc

@@ -3012,6 +3012,21 @@ bool Assembler::IsNop(SixByteInstr instr, int type) {
   return ((instr & 0xffff) == 0x1800);  // lr r0,r0
 }
 
+// dummy instruction reserved for special use.
+void Assembler::dumy(int r1, int x2, int b2, int d2) {
+#if defined(USE_SIMULATOR)
+  int op = 0xE353;
+  uint64_t code = (static_cast<uint64_t>(op & 0xFF00)) * B32 |
+                  (static_cast<uint64_t>(r1) & 0xF) * B36 |
+                  (static_cast<uint64_t>(x2) & 0xF) * B32 |
+                  (static_cast<uint64_t>(b2) & 0xF) * B28 |
+                  (static_cast<uint64_t>(d2 & 0x0FFF)) * B16 |
+                  (static_cast<uint64_t>(d2 & 0x0FF000)) >> 4 |
+                  (static_cast<uint64_t>(op & 0x00FF));
+  emit6bytes(code);
+#endif
+}
+
 void Assembler::GrowBuffer(int needed) {
   if (!own_buffer_) FATAL("external code buffer is too small");
 

src/s390/assembler-s390.h

@@ -1224,6 +1224,8 @@ class Assembler : public AssemblerBase {
 
   void nop(int type = 0);  // 0 is the default non-marking type.
 
+  void dumy(int r1, int x2, int b2, int d2);
+
   // Check the code size generated from label to here.
   int SizeOfCodeGeneratedSince(Label* label) {
     return pc_offset() - label->pos();

src/s390/constants-s390.h

@@ -915,7 +915,8 @@ enum Opcode {
   XSCH = 0xB276,      // Cancel Subchannel
   XY = 0xE357,        // Exclusive Or (32)
   ZAP = 0xF8,         // Zero And Add
-  BKPT = 0x0001       // GDB Software Breakpoint
+  BKPT = 0x0001,      // GDB Software Breakpoint
+  DUMY = 0xE353       // Special dummy opcode
 };
 
 // Instruction encoding bits and masks.

src/s390/disasm-s390.cc

@@ -1052,6 +1052,9 @@ bool Decoder::DecodeSixByte(Instruction* instr) {
 
   Opcode opcode = instr->S390OpcodeValue();
   switch (opcode) {
+    case DUMY:
+      Format(instr, "dumy\t'r1, 'd2 ( 'r2d, 'r3 )");
+      break;
     case LLILF:
       Format(instr, "llilf\t'r1,'i7");
       break;

src/s390/simulator-s390.cc

@@ -743,6 +743,7 @@ void Simulator::EvalTableInit() {
     EvalTable[i] = &Simulator::Evaluate_Unknown;
   }
 
+  EvalTable[DUMY] = &Simulator::Evaluate_DUMY;
   EvalTable[BKPT] = &Simulator::Evaluate_BKPT;
   EvalTable[SPM] = &Simulator::Evaluate_SPM;
   EvalTable[BALR] = &Simulator::Evaluate_BALR;
@@ -6058,6 +6059,12 @@ int Simulator::Evaluate_Unknown(Instruction* instr) {
   return 0;
 }
 
+EVALUATE(DUMY) {
+  DCHECK_OPCODE(DUMY);
+  // dummy instruction does nothing.
+  return 6;
+}
+
 EVALUATE(CLR) {
   DCHECK_OPCODE(CLR);
   DECODE_RR_INSTRUCTION(r1, r2);

src/s390/simulator-s390.h

@@ -522,6 +522,7 @@ class Simulator {
   static void EvalTableInit();
 
 #define EVALUATE(name) int Evaluate_##name(Instruction* instr)
+  EVALUATE(DUMY);
   EVALUATE(BKPT);
   EVALUATE(SPM);
   EVALUATE(BALR);