Avoid merging conditions across loop boundary

pkg/compiler/lib/src/ssa/codegen_helpers.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.
 
 import '../compiler.dart' show Compiler;
 import '../constants/values.dart';
 import '../elements/elements.dart';
 import '../js_backend/js_backend.dart';
 import '../types/types.dart';
 import '../universe/selector.dart' show Selector;
@@ skipping 663 matching lines @@
     if (user is HCreate) return true;
     // A [HForeign] instruction uses operators and if we generate [input] at use
     // site, the precedence or evaluation order might be wrong.
     if (user is HForeign) return false;
     // A [HCheck] instruction with control flow uses its input
     // multiple times, so we avoid generating it at use site.
     if (user is HCheck && user.isControlFlow()) return false;
     // A [HIs] instruction uses its input multiple times, so we
     // avoid generating it at use site.
     if (user is HIs) return false;
-    return true;
+    // Avoid code motion into a loop.
+    return user.hasSameLoopHeaderAs(input);
   }
 
   void visitBasicBlock(HBasicBlock block) {
     if (block.last is! HIf) return;
     HIf startIf = block.last;
     HBasicBlock end = startIf.joinBlock;
 
     // We check that the structure is the following:
     //         If
     //       /    \
@@ skipping 92 matching lines @@
     }
 
     // If [thenInput] is defined in the first predecessor, then it is only used
     // by [phi] and can be generated at use site.
     if (identical(thenInput.block, end.predecessors[0])) {
       assert(thenInput.usedBy.length == 1);
       markAsGenerateAtUseSite(thenInput);
     }
   }
 }