Enable more redundancy elimination for checked mode asserts.

runtime/vm/intermediate_language.cc

Index: runtime/vm/intermediate_language.cc
===================================================================
--- runtime/vm/intermediate_language.cc	(revision 13738)
+++ runtime/vm/intermediate_language.cc	(working copy)
@@ -86,6 +86,15 @@
 }
 
 
+bool AssertAssignableInstr::AttributesEqual(Instruction* other) const {
+  AssertAssignableInstr* other_assert = other->AsAssertAssignable();
+  ASSERT(other_assert != NULL);
+  // This predicate has to be commutative for DominatorBasedCSE to work.
+  // TODO(fschneider): Eliminate more asserts with subtype relation.
+  return dst_type().raw() == other_assert->dst_type().raw();
+}
+
+
 bool StrictCompareInstr::AttributesEqual(Instruction* other) const {
   StrictCompareInstr* other_op = other->AsStrictCompare();
   ASSERT(other_op != NULL);
@@ -1404,6 +1413,31 @@
 }
 
 
+Definition* AssertAssignableInstr::Canonicalize() {
+  // (1) Replace the assert with its input if the input has a known compatible
+  // class-id. The class-ids handled here are those that are known to be
+  // results of IL instructions.
+  intptr_t cid = value()->ResultCid();
+  bool is_redundant = false;
+  if (dst_type().IsIntType()) {
+    is_redundant = (cid == kSmiCid) || (cid == kMintCid);
+  } else if (dst_type().IsDoubleType()) {
+    is_redundant = (cid == kDoubleCid);
+  } else if (dst_type().IsBoolType()) {
+    is_redundant = (cid == kBoolCid);
+  }
+  if (is_redundant) return value()->definition();
+
+  // (2) Replace the assert with its input if the input is the result of a
+  // compatible assert itself.
+  AssertAssignableInstr* check = value()->definition()->AsAssertAssignable();
+  if ((check != NULL) && (check->dst_type().raw() == dst_type().raw())) {
+    // TODO(fschneider): Eliminate more asserts with subtype relation.
+    return check;
+  }
+  return this;
+}
+
 Definition* StrictCompareInstr::Canonicalize() {
   if (!right()->BindsToConstant()) return this;
   const Object& right_constant = right()->BoundConstant();