Implemented the Word64Clz TurboFan operator for x64, arm64, and mips64.

src/mips64/simulator-mips64.cc

 // Copyright 2011 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.
 
 #include <limits.h>
 #include <stdarg.h>
 #include <stdlib.h>
 #include <cmath>
 
 #if V8_TARGET_ARCH_MIPS64
@@ skipping 3346 matching lines @@
         DCHECK(sa() == 0);
         alu_out = get_register(HI);
       } else {
         // MIPS spec: If no bits were set in GPR rs(), the result written to
         // GPR rd() is 32.
         DCHECK(sa() == 1);
         alu_out = base::bits::CountLeadingZeros32(static_cast<int32_t>(rs_u()));
       }
       SetResult(rd_reg(), alu_out);
       break;
-    case MFLO:
-      SetResult(rd_reg(), get_register(LO));
+    case MFLO:  // MFLO == DCLZ on R6.
+      if (kArchVariant != kMips64r6) {
+        DCHECK(sa() == 0);
+        alu_out = get_register(LO);
+      } else {
+        // MIPS spec: If no bits were set in GPR rs(), the result written to
+        // GPR rd() is 64.
+        DCHECK(sa() == 1);
+        alu_out = base::bits::CountLeadingZeros64(static_cast<int64_t>(rs_u()));
+      }
+      SetResult(rd_reg(), alu_out);
       break;
     // Instructions using HI and LO registers.
     case MULT: {  // MULT == D_MUL_MUH.
       int32_t rs_lo = static_cast<int32_t>(rs());
       int32_t rt_lo = static_cast<int32_t>(rt());
       i64hilo = static_cast<int64_t>(rs_lo) * static_cast<int64_t>(rt_lo);
       if (kArchVariant != kMips64r6) {
         set_register(LO, static_cast<int32_t>(i64hilo & 0xffffffff));
         set_register(HI, static_cast<int32_t>(i64hilo >> 32));
       } else {
@@ skipping 279 matching lines @@
       alu_out = static_cast<int32_t>(rs_u()) * static_cast<int32_t>(rt_u());
       SetResult(rd_reg(), alu_out);
       // HI and LO are UNPREDICTABLE after the operation.
       set_register(LO, Unpredictable);
       set_register(HI, Unpredictable);
       break;
     case CLZ:
       // MIPS32 spec: If no bits were set in GPR rs(), the result written to
       // GPR rd is 32.
       alu_out = base::bits::CountLeadingZeros32(static_cast<uint32_t>(rs_u()));
-      set_register(rd_reg(), alu_out);
+      SetResult(rd_reg(), alu_out);
+      break;
+    case DCLZ:
+      // MIPS64 spec: If no bits were set in GPR rs(), the result written to
+      // GPR rd is 64.
+      alu_out = base::bits::CountLeadingZeros64(static_cast<uint64_t>(rs_u()));
+      SetResult(rd_reg(), alu_out);
       break;
     default:
       alu_out = 0x12345678;
       UNREACHABLE();
   }
 }
 
 
 void Simulator::DecodeTypeRegisterSPECIAL3() {
   int64_t alu_out;
@@ skipping 874 matching lines @@
 }
 
 
 #undef UNSUPPORTED
 }  // namespace internal
 }  // namespace v8
 
 #endif  // USE_SIMULATOR
 
 #endif  // V8_TARGET_ARCH_MIPS64