Optimize the multiplication of two 32-bit unsigned integers.

runtime/vm/intermediate_language_arm.cc

 // Copyright (c) 2013, 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_ARM.
 #if defined(TARGET_ARCH_ARM)
 
 #include "vm/intermediate_language.h"
 
 #include "vm/cpu.h"
@@ skipping 6112 matching lines @@
         ASSERT(op_kind() == Token::kSUB);
         __ subs(out_lo, left_lo, Operand(right_lo));
         __ sbcs(out_hi, left_hi, Operand(right_hi));
       }
       if (can_overflow()) {
         // Deopt on overflow.
         __ b(deopt, VS);
       }
       break;
     }
-    default:
-      UNREACHABLE();
-    break;
+    case Token::kMUL: {
+      // We only support the multiplication of two positive 32-bit integers
+      // resulting in a positive 64-bit integer fitting in a mint.
+      // We deopt in all other cases.
+      // This guarantees that the multiplication of 16-bit unsigned integers,
+      // as used in bignum arithmetic, will always succeed.
+      if (TargetCPUFeatures::arm_version() == ARMv7) {
+        __ orrs(out_hi, left_hi, Operand(right_hi));
+        __ b(deopt, NE);
+        __ smull(out_lo, out_hi, left_lo, right_lo);
+        if (can_overflow()) {
+          __ TestImmediate(out_hi, 0xC0000000);
+          __ b(deopt, NE);
+        }
+      } else {
+        __ b(deopt);
+      }
+      break;
+    }
+    default: UNREACHABLE();
   }
   if (FLAG_throw_on_javascript_int_overflow) {
     EmitJavascriptIntOverflowCheck(compiler, deopt, out_lo, out_hi);
   }
 }
 
 
 LocationSummary* ShiftMintOpInstr::MakeLocationSummary(Isolate* isolate,
                                                        bool opt) const {
   const intptr_t kNumInputs = 2;
@@ skipping 670 matching lines @@
   compiler->GenerateCall(token_pos(), &label, stub_kind_, locs());
 #if defined(DEBUG)
   __ LoadImmediate(R4, kInvalidObjectPointer);
   __ LoadImmediate(R5, kInvalidObjectPointer);
 #endif
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM