Implement a branch optimization pass.

runtime/vm/intermediate_language.cc

Index: runtime/vm/intermediate_language.cc
diff --git a/runtime/vm/intermediate_language.cc b/runtime/vm/intermediate_language.cc
index 177ba92198e491affb6f187b8f59b3f729787e62..b8423951c07f6b68378be728f2426b6d7492f38d 100644
--- a/runtime/vm/intermediate_language.cc
+++ b/runtime/vm/intermediate_language.cc
@@ -497,6 +497,15 @@ void Value::RemoveFromUseList() {
 }
 
 
+bool Definition::HasOnlyUse(Value* use) const {
+  if (((input_use_list() == use) && (env_use_list() == NULL)) ||
+      ((input_use_list() == NULL) && (env_use_list() == use))) {
+    return (use->next_use() == NULL);
+  }
+  return false;
+}
+
+
 void Definition::ReplaceUsesWith(Definition* other) {
   ASSERT(other != NULL);
   ASSERT(this != other);
@@ -1163,6 +1172,11 @@ bool LoadFieldInstr::IsFixedLengthArrayCid(intptr_t cid) {
 }
 
 
+Definition* ConstantInstr::Canonicalize(FlowGraphOptimizer* optimizer) {
+  return HasUses() ? this : NULL;

[Vyacheslav Egorov (Google), 2013/03/06 16:44:22]

I'd really like to see a more generic dead code elimination pass.

[Kevin Millikin (Google), 2013/03/08 10:38:10]

Me too, but this doesn't really seem like an abuse of Canonicalize to me.

+}
+
+
 Definition* LoadFieldInstr::Canonicalize(FlowGraphOptimizer* optimizer) {
   if (!IsImmutableLengthLoad()) return this;