Improve SHR by using range information for the shift count.

runtime/vm/intermediate_language_x64.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_X64.
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/intermediate_language.h"
 
 #include "lib/error.h"
@@ skipping 1742 matching lines @@
       __ cqo();  // Sign extend RAX -> RDX:RAX.
       __ idivq(right_temp);  //  RAX: quotient, RDX: remainder.
       // Check the corner case of dividing the 'MIN_SMI' with -1, in which
       // case we cannot tag the result.
       __ cmpq(result, Immediate(0x4000000000000000));
       __ j(EQUAL, deopt);
       __ SmiTag(result);
       break;
     }
     case Token::kSHR: {
+      if (CanDeoptimize()) {
+        __ cmpq(right, Immediate(0));
+        __ j(LESS, deopt);
+      }
+      __ SmiUntag(right);
       // sarq operation masks the count to 6 bits.
-      const Immediate kCountLimit = Immediate(0x3F);
-      __ cmpq(right, Immediate(0));
-      __ j(LESS, deopt);
-      __ SmiUntag(right);
-      __ cmpq(right, kCountLimit);
-      Label count_ok;
-      __ j(LESS, &count_ok, Assembler::kNearJump);
-      __ movq(right, kCountLimit);
-      __ Bind(&count_ok);
+      const intptr_t kCountLimit = 0x3F;
+      Range* right_range = this->right()->definition()->range();
+      if ((right_range == NULL) ||
+          !right_range->IsWithin(RangeBoundary::kMinusInfinity, kCountLimit)) {
+        __ cmpq(right, Immediate(kCountLimit));
+        Label count_ok;
+        __ j(LESS, &count_ok, Assembler::kNearJump);
+        __ movq(right, Immediate(kCountLimit));
+        __ Bind(&count_ok);
+      }
       ASSERT(right == RCX);  // Count must be in RCX
       __ SmiUntag(left);
       __ sarq(left, right);
       __ SmiTag(left);
       break;
     }
     case Token::kSHL: {
       Register temp = locs()->temp(0).reg();
       // Check if count too large for handling it inlined.
       __ movq(temp, left);
@@ skipping 550 matching lines @@
 
 void ShiftMintOpInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
   UNIMPLEMENTED();
 }
 
 }  // namespace dart
 
 #undef __
 
 #endif  // defined TARGET_ARCH_X64