ARM64: Reland faster immediate check

src/arm64/macro-assembler-arm64.cc

 // Copyright 2013 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 "src/v8.h"
 
 #if V8_TARGET_ARCH_ARM64
 
 #include "src/bootstrapper.h"
 #include "src/codegen.h"
@@ skipping 46 matching lines @@
   UseScratchRegisterScope temps(this);
 
   if (operand.NeedsRelocation(this)) {
     Register temp = temps.AcquireX();
     Ldr(temp, operand.immediate());
     Logical(rd, rn, temp, op);
 
   } else if (operand.IsImmediate()) {
     int64_t immediate = operand.ImmediateValue();
     unsigned reg_size = rd.SizeInBits();
-    ASSERT(rd.Is64Bits() || is_uint32(immediate));
 
     // If the operation is NOT, invert the operation and immediate.
     if ((op & NOT) == NOT) {
       op = static_cast<LogicalOp>(op & ~NOT);
       immediate = ~immediate;
-      if (rd.Is32Bits()) {
-        immediate &= kWRegMask;
-      }
     }
 
+    // Ignore the top 32 bits of an immediate if we're moving to a W register.
+    if (rd.Is32Bits()) {
+      // Check that the top 32 bits are consistent.
+      ASSERT(((immediate >> kWRegSizeInBits) == 0) ||
+             ((immediate >> kWRegSizeInBits) == -1));
+      immediate &= kWRegMask;
+    }
+
+    ASSERT(rd.Is64Bits() || is_uint32(immediate));
+
     // Special cases for all set or all clear immediates.
     if (immediate == 0) {
       switch (op) {
         case AND:
           Mov(rd, 0);
           return;
         case ORR:  // Fall through.
         case EOR:
           Mov(rd, rn);
           return;
@@ skipping 5216 matching lines @@
   }
 }
 
 
 #undef __
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM64