Use sourceElement when eliminating Phis

pkg/compiler/lib/src/ssa/optimize.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 '../common/codegen.dart' show CodegenRegistry, CodegenWorkItem;
 import '../common/names.dart' show Selectors;
 import '../common/tasks.dart' show CompilerTask;
 import '../compiler.dart' show Compiler;
 import '../constants/constant_system.dart';
 import '../constants/values.dart';
@@ skipping 217 matching lines @@
           // If we can replace [instruction] with [replacement], then
           // [replacement]'s type can be narrowed.
           TypeMask newType = replacement.instructionType
               .intersection(instruction.instructionType, _closedWorld);
           replacement.instructionType = newType;
         }
 
         // If the replacement instruction does not know its
         // source element, use the source element of the
         // instruction.
-        if (replacement.sourceElement == null) {
-          replacement.sourceElement = instruction.sourceElement;
-        }
-        if (replacement.sourceInformation == null) {
-          replacement.sourceInformation = instruction.sourceInformation;
-        }
+        replacement.sourceElement ??= instruction.sourceElement;
+        replacement.sourceInformation ??= instruction.sourceInformation;
         if (!replacement.isInBasicBlock()) {
           // The constant folding can return an instruction that is already
           // part of the graph (like an input), so we only add the replacement
           // if necessary.
           block.addAfter(instruction, replacement);
           // Visit the replacement as the next instruction in case it
           // can also be constant folded away.
           next = replacement;
         }
         block.remove(instruction);
@@ skipping 1499 matching lines @@
       //
       // TODO(sra): If the input is directly in the only live predecessor, it
       // might be possible to move it into [block] (e.g. all its inputs are
       // dominating.)
       block.forEachPhi((HPhi phi) {
         HInstruction replacement =
             (indexOfLive >= 0) ? phi.inputs[indexOfLive] : zapInstruction;
         if (replacement.dominates(phi)) {
           block.rewrite(phi, replacement);
           block.removePhi(phi);
+          if (replacement.sourceElement == null &&
+              phi.sourceElement != null &&
+              replacement is! HThis) {
+            replacement.sourceElement = phi.sourceElement;
+          }
         }
       });
     }
   }
 
   void replaceInput(int i, HInstruction from, HInstruction by) {
     from.inputs[i].usedBy.remove(from);
     from.inputs[i] = by;
     by.usedBy.add(from);
   }
@@ skipping 185 matching lines @@
       if (candidate == null) continue;
 
       // Because we're updating the users of this phi, we may have new
       // phis candidate for elimination. Add phis that used this phi
       // to the worklist.
       for (final user in phi.usedBy) {
         if (user is HPhi) worklist.add(user);
       }
       phi.block.rewrite(phi, candidate);
       phi.block.removePhi(phi);
+      if (candidate.sourceElement == null &&
+          phi.sourceElement != null &&
+          candidate is! HThis) {
+        candidate.sourceElement = phi.sourceElement;
+      }
     }
   }
 }
 
 class GvnWorkItem {
   final HBasicBlock block;
   final ValueSet valueSet;
   GvnWorkItem(this.block, this.valueSet);
 }
 
@@ skipping 998 matching lines @@
 
     keyedValues.forEach((receiver, values) {
       result.keyedValues[receiver] =
           new Map<HInstruction, HInstruction>.from(values);
     });
 
     result.nonEscapingReceivers.addAll(nonEscapingReceivers);
     return result;
   }
 }