Optimize the assembly code generated for Math.random()

src/x64/disasm-x64.cc

 // Copyright 2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 979 matching lines @@
 // We do not use any three-byte opcodes, which start with 0x0F38 or 0x0F3A.
 int DisassemblerX64::TwoByteOpcodeInstruction(byte* data) {
   byte opcode = *(data + 1);
   byte* current = data + 2;
   // At return, "current" points to the start of the next instruction.
   const char* mnemonic = TwoByteMnemonic(opcode);
   if (operand_size_ == 0x66) {
     // 0x66 0x0F prefix.
     int mod, regop, rm;
     get_modrm(*current, &mod, &regop, &rm);
-    const char* mnemonic = "?";
-    if (opcode == 0x57) {
-      mnemonic = "xorpd";
-    } else if (opcode == 0x2E) {
-      mnemonic = "comisd";
-    } else if (opcode == 0x2F) {
-      mnemonic = "ucomisd";
+    if (opcode == 0x6E) {
+      AppendToBuffer("movd %s,", NameOfXMMRegister(regop));
+      current += PrintRightOperand(current);
     } else {
-      UnimplementedInstruction();
+      const char* mnemonic = "?";
+      if (opcode == 0x57) {
+        mnemonic = "xorpd";
+      } else if (opcode == 0x2E) {
+        mnemonic = "comisd";
+      } else if (opcode == 0x2F) {
+        mnemonic = "ucomisd";
+      } else {
+        UnimplementedInstruction();
+      }
+      AppendToBuffer("%s %s,", mnemonic, NameOfXMMRegister(regop));
+      current += PrintRightXMMOperand(current);
     }
-    AppendToBuffer("%s %s,", mnemonic, NameOfXMMRegister(regop));
-    current += PrintRightXMMOperand(current);
   } else if (group_1_prefix_ == 0xF2) {
     // Beginning of instructions with prefix 0xF2.
 
     if (opcode == 0x11 || opcode == 0x10) {
       // MOVSD: Move scalar double-precision fp to/from/between XMM registers.
       AppendToBuffer("movsd ");
       int mod, regop, rm;
       get_modrm(*current, &mod, &regop, &rm);
       if (opcode == 0x11) {
         current += PrintRightOperand(current);
@@ skipping 10 matching lines @@
       current += PrintRightOperand(current);
     } else if ((opcode & 0xF8) == 0x58) {
       // XMM arithmetic. Mnemonic was retrieved at the start of this function.
       int mod, regop, rm;
       get_modrm(*current, &mod, &regop, &rm);
       AppendToBuffer("%s %s,", mnemonic, NameOfXMMRegister(regop));
       current += PrintRightXMMOperand(current);
     } else {
       UnimplementedInstruction();
     }
-  } else if (opcode == 0x2C && group_1_prefix_ == 0xF3) {
-    // Instruction with prefix 0xF3.
-
-    // CVTTSS2SI: Convert scalar single-precision FP to dword integer.
-    // Assert that mod is not 3, so source is memory, not an XMM register.
-    ASSERT_NE(0xC0, *current & 0xC0);
-    current += PrintOperands("cvttss2si", REG_OPER_OP_ORDER, current);
+  } else if (group_1_prefix_ == 0xF3) {
+    // Instructions with prefix 0xF3.
+    if (opcode == 0x2C) {
+      // CVTTSS2SI: Convert scalar single-precision FP to dword integer.
+      // Assert that mod is not 3, so source is memory, not an XMM register.
+      ASSERT_NE(0xC0, *current & 0xC0);
+      current += PrintOperands("cvttss2si", REG_OPER_OP_ORDER, current);
+    } else if (opcode == 0x5A) {
+      int mod, regop, rm;
+      get_modrm(*current, &mod, &regop, &rm);
+      AppendToBuffer("cvtss2sd %s,", NameOfXMMRegister(regop));
+      current += PrintRightXMMOperand(current);
+    } else {
+      UnimplementedInstruction();
+    }
   } else if (opcode == 0x1F) {
     // NOP
     int mod, regop, rm;
     get_modrm(*current, &mod, &regop, &rm);
     current++;
     if (regop == 4) {  // SIB byte present.
       current++;
     }
     if (mod == 1) {  // Byte displacement.
       current += 1;
@@ skipping 569 matching lines @@
       fprintf(f, "%02x", *bp);
     }
     for (int i = 6 - static_cast<int>(pc - prev_pc); i >= 0; i--) {
       fprintf(f, "  ");
     }
     fprintf(f, "  %s\n", buffer.start());
   }
 }
 
 }  // namespace disasm