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taichi/analysis/gather_immutable_local_vars.cpp

@@ -5,6 +5,10 @@
 
 namespace taichi::lang {
 
+// The GatherImmutableLocalVars pass gathers all immutable local vars as input
+// to the EliminateImmutableLocalVars pass. An immutable local var is an alloca
+// which is stored only once (in the same block) and only loaded after that
+// store.
 class GatherImmutableLocalVars : public BasicStmtVisitor {
  private:
   using BasicStmtVisitor::visit;

taichi/transforms/eliminate_immutable_local_vars.cpp

@@ -6,12 +6,16 @@
 
 namespace taichi::lang {
 
+// The EliminateImmutableLocalVars pass eliminates all immutable local vars
+// calculated from the GatherImmutableLocalVars pass. An immutable local var
+// can be eliminated by forwarding the value of its only store to all loads
+// after that store. See https://github.com/taichi-dev/taichi/pull/6926 for the
+// background of this optimization.
 class EliminateImmutableLocalVars : public BasicStmtVisitor {
  private:
   using BasicStmtVisitor::visit;
 
   DelayedIRModifier modifier_;
-
   std::unordered_set<Stmt *> immutable_local_vars_;
   std::unordered_map<Stmt *, Stmt *> immutable_local_var_to_value_;