When doing SSA type propagation, refine the receiver after a call.

sdk/lib/_internal/compiler/implementation/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.
 
 part of ssa;
 
 /**
+ * Remove [HTypeKnown] instructions from the graph, to make codegen
+ * analysis easier.
+ */
+class SsaTypeKnownRemover extends HBaseVisitor {
+
+  void visitGraph(HGraph graph) {
+    visitDominatorTree(graph);
+  }
+
+  void visitBasicBlock(HBasicBlock block) {
+    HInstruction instruction = block.first;
+    while (instruction != null) {
+      HInstruction next = instruction.next;
+      instruction.accept(this);
+      instruction = next;
+    }
+  }
+
+  void visitTypeKnown(HTypeKnown instruction) {
+    instruction.block.rewrite(instruction, instruction.checkedInput);
+    instruction.block.remove(instruction);
+  }
+}
+
+/**
  * Instead of emitting each SSA instruction with a temporary variable
  * mark instructions that can be emitted at their use-site.
  * For example, in:
  *   t0 = 4;
  *   t1 = 3;
  *   t2 = add(t0, t1);
  * t0 and t1 would be marked and the resulting code would then be:
  *   t2 = add(4, 3);
  */
 class SsaInstructionMerger extends HBaseVisitor {
@@ skipping 94 matching lines @@
         && !instruction.isReceiverTypeCheck) {
       assert(instruction.isCheckedModeCheck || instruction.isCastTypeCheck);
       // Checked mode checks and cast checks compile to code that
       // only use their input once, so we can safely visit them
       // and try to merge the input.
       visitInstruction(instruction);
     }
   }
 
   void visitTypeKnown(HTypeKnown instruction) {
-    markAsGenerateAtUseSite(instruction);
+    // [HTypeKnown] instructions are removed before code generation.
+    assert(false);
   }
 
   void tryGenerateAtUseSite(HInstruction instruction) {
     if (instruction.isControlFlow()) return;
     markAsGenerateAtUseSite(instruction);
   }
 
   bool isBlockSinglePredecessor(HBasicBlock block) {
     return block.successors.length == 1
         && block.successors[0].predecessors.length == 1;
@@ skipping 244 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);
     }
   }
 }