MIPS64: r6 compact branch optimization.

src/mips64/disasm-mips64.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // A Disassembler object is used to disassemble a block of code instruction by
 // instruction. The default implementation of the NameConverter object can be
 // overriden to modify register names or to do symbol lookup on addresses.
 //
 // The example below will disassemble a block of code and print it to stdout.
 //
@@ skipping 73 matching lines @@
   void PrintSecondaryField(Instruction* instr);
   void PrintUImm16(Instruction* instr);
   void PrintSImm16(Instruction* instr);
   void PrintXImm16(Instruction* instr);
   void PrintPCImm16(Instruction* instr, int delta_pc, int n_bits);
   void PrintXImm18(Instruction* instr);
   void PrintSImm18(Instruction* instr);
   void PrintXImm19(Instruction* instr);
   void PrintSImm19(Instruction* instr);
   void PrintXImm21(Instruction* instr);
-
+  void PrintSImm21(Instruction* instr);
   void PrintPCImm21(Instruction* instr, int delta_pc, int n_bits);
   void PrintXImm26(Instruction* instr);
   void PrintSImm26(Instruction* instr);
   void PrintPCImm26(Instruction* instr, int delta_pc, int n_bits);
   void PrintPCImm26(Instruction* instr);
   void PrintCode(Instruction* instr);   // For break and trap instructions.
   void PrintFormat(Instruction* instr);  // For floating format postfix.
   void PrintBp2(Instruction* instr);
   void PrintBp3(Instruction* instr);
   // Printing of instruction name.
@@ skipping 225 matching lines @@
 }
 
 
 // Print 21-bit immediate value.
 void Decoder::PrintXImm21(Instruction* instr) {
   uint32_t imm = instr->Imm21Value();
   out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_, "0x%x", imm);
 }
 
 
+// Print 21-bit signed immediate value.
+void Decoder::PrintSImm21(Instruction* instr) {
+  int32_t imm21 = instr->Imm21Value();
+  // set sign
+  imm21 <<= (32 - kImm21Bits);
+  imm21 >>= (32 - kImm21Bits);
+  out_buffer_pos_ += SNPrintF(out_buffer_ + out_buffer_pos_, "%d", imm21);
+}
+
+
 // Print absoulte address for 21-bit offset or immediate value.
 // The absolute address is calculated according following expression:
 //      PC + delta_pc + (offset << n_bits)
 void Decoder::PrintPCImm21(Instruction* instr, int delta_pc, int n_bits) {
   int32_t imm21 = instr->Imm21Value();
   // set sign
   imm21 <<= (32 - kImm21Bits);
   imm21 >>= (32 - kImm21Bits);
   out_buffer_pos_ +=
       SNPrintF(out_buffer_ + out_buffer_pos_, "%s",
@@ skipping 257 matching lines @@
             case 'x':
               DCHECK(STRING_STARTS_WITH(format, "imm19x"));
               PrintXImm19(instr);
               break;
           }
           return 6;
         }
       } else if (format[3] == '2' && format[4] == '1') {
         DCHECK(STRING_STARTS_WITH(format, "imm21"));
         switch (format[5]) {
+          case 's':
+            DCHECK(STRING_STARTS_WITH(format, "imm21s"));
+            PrintSImm21(instr);
+            break;
           case 'x':
             DCHECK(STRING_STARTS_WITH(format, "imm21x"));
             PrintXImm21(instr);
             break;
           case 'p': {  // The PC relative address.
             DCHECK(STRING_STARTS_WITH(format, "imm21p"));
             int delta_pc = 0;
             int n_bits = 0;
             switch (format[6]) {
               case '4': {
@@ skipping 971 matching lines @@
       Format(instr, "balc    'imm26s -> 'imm26p4s2");
       break;
     case BNE:
       Format(instr, "bne     'rs, 'rt, 'imm16u -> 'imm16p4s2");
       break;
     case BLEZ:
       if ((instr->RtValue() == 0) && (instr->RsValue() != 0)) {
         Format(instr, "blez    'rs, 'imm16u -> 'imm16p4s2");
       } else if ((instr->RtValue() != instr->RsValue()) &&
                  (instr->RsValue() != 0) && (instr->RtValue() != 0)) {
-        Format(instr, "bgeuc    'rs, 'rt, 'imm16u -> 'imm16p4s2");
+        Format(instr, "bgeuc   'rs, 'rt, 'imm16u -> 'imm16p4s2");
       } else if ((instr->RtValue() == instr->RsValue()) &&
                  (instr->RtValue() != 0)) {
-        Format(instr, "bgezalc  'rs, 'imm16u -> 'imm16p4s2");
+        Format(instr, "bgezalc 'rs, 'imm16u -> 'imm16p4s2");
       } else if ((instr->RsValue() == 0) && (instr->RtValue() != 0)) {
-        Format(instr, "blezalc  'rt, 'imm16u -> 'imm16p4s2");
+        Format(instr, "blezalc 'rt, 'imm16u -> 'imm16p4s2");
       } else {
         UNREACHABLE();
       }
       break;
     case BGTZ:
       if ((instr->RtValue() == 0) && (instr->RsValue() != 0)) {
         Format(instr, "bgtz    'rs, 'imm16u -> 'imm16p4s2");
       } else if ((instr->RtValue() != instr->RsValue()) &&
                  (instr->RsValue() != 0) && (instr->RtValue() != 0)) {
         Format(instr, "bltuc   'rs, 'rt, 'imm16u -> 'imm16p4s2");
@@ skipping 16 matching lines @@
         Format(instr, "blezc    'rt, 'imm16u -> 'imm16p4s2");
       } else {
         UNREACHABLE();
       }
       break;
     case BGTZL:
       if ((instr->RtValue() == instr->RsValue()) && (instr->RtValue() != 0)) {
         Format(instr, "bltzc    'rt, 'imm16u -> 'imm16p4s2");
       } else if ((instr->RtValue() != instr->RsValue()) &&
                  (instr->RsValue() != 0) && (instr->RtValue() != 0)) {
-        Format(instr, "bltc     'rs, 'rt, 'imm16u -> 'imm16p4s2");
+        Format(instr, "bltc    'rs, 'rt, 'imm16u -> 'imm16p4s2");
       } else if ((instr->RsValue() == 0) && (instr->RtValue() != 0)) {
         Format(instr, "bgtzc    'rt, 'imm16u -> 'imm16p4s2");
       } else {
         UNREACHABLE();
       }
       break;
     case POP66:
       if (instr->RsValue() == JIC) {
         Format(instr, "jic     'rt, 'imm16s");
       } else {
-        Format(instr, "beqzc   'rs, 'imm21x -> 'imm21p4s2");
+        Format(instr, "beqzc   'rs, 'imm21s -> 'imm21p4s2");
       }
       break;
     case POP76:
       if (instr->RsValue() == JIALC) {
-        Format(instr, "jialc   'rt, 'imm16x");
+        Format(instr, "jialc   'rt, 'imm16s");
       } else {
-        Format(instr, "bnezc   'rs, 'imm21x -> 'imm21p4s2");
+        Format(instr, "bnezc   'rs, 'imm21s -> 'imm21p4s2");
       }
       break;
     // ------------- Arithmetic instructions.
     case ADDI:
       if (kArchVariant != kMips64r6) {
         Format(instr, "addi    'rt, 'rs, 'imm16s");
       } else {
-        // Check if BOVC or BEQC instruction.
-        if (instr->RsValue() >= instr->RtValue()) {
+        int rs_reg = instr->RsValue();
+        int rt_reg = instr->RtValue();
+        // Check if BOVC, BEQZALC or BEQC instruction.
+        if (rs_reg >= rt_reg) {
           Format(instr, "bovc  'rs, 'rt, 'imm16s -> 'imm16p4s2");
-        } else if (instr->RsValue() < instr->RtValue()) {
-          Format(instr, "beqc  'rs, 'rt, 'imm16s -> 'imm16p4s2");
         } else {

[Ilija.Pavlovic1, 2015/12/18 11:38:22]

One of conditions is (rt_reg != 0):

if (rt_reg != 0) {
    if (rs_reg == 0) { ... }
    else { ... }
} else { // rt_reg == 0
    UNREACHABLE(); 
}

[balazs.kilvady, 2015/12/18 19:18:05]

One more thing to backport...

[ivica.bogosavljevic, 2015/12/22 10:22:40]

I'll add DCHECK(rt_reg > 0) before if (rs_reg == 0)

[ivica.bogosavljevic, 2015/12/22 10:22:40]

Acknowledged.

-          UNREACHABLE();
+          if (rs_reg == 0) {
+            Format(instr, "beqzalc 'rt, 'imm16s -> 'imm16p4s2");
+          } else {
+            Format(instr, "beqc    'rs, 'rt, 'imm16s -> 'imm16p4s2");
+          }
         }
       }
       break;
     case DADDI:
       if (kArchVariant != kMips64r6) {
         Format(instr, "daddi   'rt, 'rs, 'imm16s");
       } else {
-        // Check if BNVC or BNEC instruction.
-        if (instr->RsValue() >= instr->RtValue()) {
+        int rs_reg = instr->RsValue();
+        int rt_reg = instr->RtValue();
+        // Check if BNVC, BNEZALC or BNEC instruction.
+        if (rs_reg >= rt_reg) {
           Format(instr, "bnvc  'rs, 'rt, 'imm16s -> 'imm16p4s2");
-        } else if (instr->RsValue() < instr->RtValue()) {
-          Format(instr, "bnec  'rs, 'rt, 'imm16s -> 'imm16p4s2");
         } else {

[Ilija.Pavlovic1, 2015/12/18 11:38:22]

One of conditions is (rt_reg != 0):

if (rt_reg != 0) {
    if (rs_reg == 0) { ... }
    else { ... }
} else { // rt_reg == 0
    UNREACHABLE(); 
}

[ivica.bogosavljevic, 2015/12/22 10:22:40]

I'll add DCHECK(rt_reg > 0) before if (rs_reg == 0)

-          UNREACHABLE();
+          if (rs_reg == 0) {
+            Format(instr, "bnezalc 'rt, 'imm16s -> 'imm16p4s2");
+          } else {
+            Format(instr, "bnec  'rs, 'rt, 'imm16s -> 'imm16p4s2");
+          }
         }
       }
       break;
     case ADDIU:
       Format(instr, "addiu   'rt, 'rs, 'imm16s");
       break;
     case DADDIU:
       Format(instr, "daddiu  'rt, 'rs, 'imm16s");
       break;
     case SLTI:
@@ skipping 264 matching lines @@
         prev_pc, *reinterpret_cast<int32_t*>(prev_pc), buffer.start());
   }
 }
 
 
 #undef UNSUPPORTED
 
 }  // namespace disasm
 
 #endif  // V8_TARGET_ARCH_MIPS64