[x64] Improve key value sign-extension of dehoisted LoadKeyed/StoreKeyed

src/x64/lithium-gap-resolver-x64.cc

 // Copyright 2011 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 180 matching lines @@
       __ movp(dst, kScratchRegister);
     }
 
   } else if (source->IsConstantOperand()) {
     LConstantOperand* constant_source = LConstantOperand::cast(source);
     if (destination->IsRegister()) {
       Register dst = cgen_->ToRegister(destination);
       if (cgen_->IsSmiConstant(constant_source)) {
         __ Move(dst, cgen_->ToSmi(constant_source));
       } else if (cgen_->IsInteger32Constant(constant_source)) {
-        __ Set(dst, static_cast<uint32_t>(cgen_->ToInteger32(constant_source)));
+        int32_t constant = cgen_->ToInteger32(constant_source);
+        // Do sign extension only for constant used as de-hoisted array key.
+        // Others only need zero extension, which saves 2 bytes.
+        if (cgen_->IsDehoistedKeyConstant(constant_source)) {
+          __ Set(dst, constant);
+        } else {
+          __ Set(dst, static_cast<uint32_t>(constant));
+        }
       } else {
         __ Move(dst, cgen_->ToHandle(constant_source));
       }
     } else if (destination->IsDoubleRegister()) {
       double v = cgen_->ToDouble(constant_source);
       uint64_t int_val = BitCast<uint64_t, double>(v);
       XMMRegister dst = cgen_->ToDoubleRegister(destination);
       if (int_val == 0) {
         __ xorps(dst, dst);
       } else {
         __ Set(kScratchRegister, int_val);
         __ movq(dst, kScratchRegister);
       }
     } else {
       ASSERT(destination->IsStackSlot());
       Operand dst = cgen_->ToOperand(destination);
       if (cgen_->IsSmiConstant(constant_source)) {
         __ Move(dst, cgen_->ToSmi(constant_source));
       } else if (cgen_->IsInteger32Constant(constant_source)) {
-        // Zero top 32 bits of a 64 bit spill slot that holds a 32 bit untagged
-        // value.
+        // Do sign extension to 64 bits when stored into stack slot.
         __ movp(dst, Immediate(cgen_->ToInteger32(constant_source)));
       } else {
         __ Move(kScratchRegister, cgen_->ToHandle(constant_source));
         __ movp(dst, kScratchRegister);
       }
     }
 
   } else if (source->IsDoubleRegister()) {
     XMMRegister src = cgen_->ToDoubleRegister(source);
     if (destination->IsDoubleRegister()) {
@@ skipping 94 matching lines @@
       moves_[i].set_source(source);
     }
   }
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64