Insert type guards for loads from arrays in nested loops.

lib/compiler/implementation/ssa/bailout.dart

 // 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.
 
 class BailoutInfo {
   int instructionId;
   int bailoutId;
   BailoutInfo(this.instructionId, this.bailoutId);
 }
 
@@ skipping 89 matching lines @@
       instruction = instruction.next;
     }
   }
 
   // Primitive types that are not null are valuable. These include
   // indexable arrays.
   bool typeValuable(HType type) {
     return type.isPrimitive() && !type.isNull();
   }
 
+  bool get hasTypeGuards() => work.guards.length != 0;
+
   bool typeGuardWouldBeValuable(HInstruction instruction,
                                 HType speculativeType) {
     // If the type itself is not valuable, do not generate a guard for it.
     if (!typeValuable(speculativeType)) return false;
 
     // Do not insert a type guard if the instruction has a type
     // annotation that disagrees with the speculated type.
     Element source = instruction.sourceElement;
     if (source !== null) {
       Type sourceType = source.computeType(compiler);
@@ skipping 18 matching lines @@
       return false;
     }
 
     // If the instruction is not in a loop then the header will be null.
     HBasicBlock currentLoopHeader = instruction.block.enclosingLoopHeader;
     for (HInstruction user in instruction.usedBy) {
       HBasicBlock userLoopHeader = user.block.enclosingLoopHeader;
       if (isNested(userLoopHeader, currentLoopHeader)) return true;
     }
 
+    // To speed up computations on values loaded from arrays, we
+    // insert type guards for builtin array indexing operations in
+    // nested loops. Since this can blow up code size quite
+    // significantly, we only do it if type guards have already been
+    // inserted for this method. The code size price for an additional
+    // type guard is much smaller than the first one that causes the
+    // generation of a bailout method.
+    if (instruction is HIndex && instruction.builtin && hasTypeGuards) {
+      HBasicBlock loopHeader = instruction.block.enclosingLoopHeader;
+      if (loopHeader != null && loopHeader.parentLoopHeader != null) {
+        return true;
+      }
+    }
+
     // Insert type guards if the method is likely to be called in a
     // loop.
     return calledInLoop || highTypeLikelyhood;
   }
 
   bool shouldInsertTypeGuard(HInstruction instruction) {
     HType speculativeType = instruction.propagatedType;
     HType computedType = instruction.computeTypeFromInputTypes();
     // Start by reverting the propagated type. If we add a type guard then the
     // guard will expose the speculative type. If we don't add a type guard
@@ skipping 362 matching lines @@
         hasComplexTypeGuards = true;
       }
     } else {
       hasComplexTypeGuards = true;
       blocks.forEach((HBasicBlock block) {
         block.guards.add(guard);
       });
     }
   }
 }