[opt] Simplify replace_statements and improve demote_dense_struct_fors (

#2335)

* [opt] Simplify replace_statements and improve demote_dense_struct_fors

* Apply review

taichi/ir/transforms.h

@@ -75,25 +75,30 @@ bool constant_fold(IRNode *root,
                    const CompileConfig &config,
                    const ConstantFoldPass::Args &args);
 void offload(IRNode *root, const CompileConfig &config);
+bool transform_statements(
+    IRNode *root,
+    std::function<bool(Stmt *)> filter,
+    std::function<void(Stmt *, DelayedIRModifier *)> transformer);
 /**
  * @param root The IR root to be traversed.
  * @param filter A function which tells if a statement need to be replaced.
- * @param generator If a statement s need to be replaced, generate a new
- * statement s1 with the argument s, insert s1 to s's place, and replace all
- * usages of s with s1.
+ * @param generator If a statement |s| need to be replaced, generate a new
+ * statement |s1| with the argument |s|, insert |s1| to where |s| is defined,
+ * remove |s|'s definition, and replace all usages of |s| with |s1|.
+ * @return Whether the IR is modified.
  */
-void replace_statements_with(
+bool replace_and_insert_statements(
     IRNode *root,
     std::function<bool(Stmt *)> filter,
     std::function<std::unique_ptr<Stmt>(Stmt *)> generator);
 /**
- * @param generator If a statement s need to be replaced, find the existing
- * statement s1 with the argument s, and replace all usages of s with s1.
- * @return Whether the IR is modified.
+ * @param finder If a statement |s| need to be replaced, find the existing
+ * statement |s1| with the argument |s|, remove |s|'s definition, and replace
+ * all usages of |s| with |s1|.
  */
-bool replace_statements_with(IRNode *root,
-                             std::function<bool(Stmt *)> filter,
-                             std::function<Stmt *(Stmt *)> generator);
+bool replace_statements(IRNode *root,
+                        std::function<bool(Stmt *)> filter,
+                        std::function<Stmt *(Stmt *)> finder);
 void demote_dense_struct_fors(IRNode *root);
 bool demote_atomics(IRNode *root, const CompileConfig &config);
 void reverse_segments(IRNode *root);  // for autograd

taichi/transforms/demote_dense_struct_fors.cpp

@@ -86,21 +86,22 @@ void convert_to_range_for(OffloadedStmt *offloaded) {
     }
   }
 
-  for (int i = 0; i < num_loop_vars; i++) {
-    // TODO: Use only one (instead num_loop_vars) invocation(s) of
-    //  replace_statements_with
-    irpass::replace_statements_with(
-        body.get(),
-        [&](Stmt *s) {
-          if (auto loop_index = s->cast<LoopIndexStmt>()) {
-            return loop_index->loop == offloaded &&
-                   loop_index->index ==
-                       snodes.back()->physical_index_position[i];
-          }
+  irpass::replace_statements(
+      body.get(), /*filter=*/
+      [&](Stmt *s) {
+        if (auto loop_index = s->cast<LoopIndexStmt>()) {
+          return loop_index->loop == offloaded;
+        } else {
           return false;
-        },
-        [&](Stmt *) { return new_loop_vars[i]; });
-  }
+        }
+      },
+      /*finder=*/
+      [&](Stmt *s) {
+        auto index = std::find(physical_indices.begin(), physical_indices.end(),
+                               s->as<LoopIndexStmt>()->index);
+        TI_ASSERT(index != physical_indices.end());
+        return new_loop_vars[index - physical_indices.begin()];
+      });
 
   if (has_test) {
     // Create an If statement

taichi/transforms/inlining.cpp

@@ -24,12 +24,10 @@ class Inliner : public BasicStmtVisitor {
     TI_ASSERT(func->rets.size() <= 1);
     auto inlined_ir = irpass::analysis::clone(func->ir.get());
     if (!func->args.empty()) {
-      // TODO: Make sure that if stmt->args is an ArgLoadStmt,
-      //  it will not be replaced again here
-      irpass::replace_statements_with(
+      irpass::replace_statements(
           inlined_ir.get(),
           /*filter=*/[&](Stmt *s) { return s->is<ArgLoadStmt>(); },
-          /*generator=*/
+          /*finder=*/
           [&](Stmt *s) { return stmt->args[s->as<ArgLoadStmt>()->arg_id]; });
     }
     if (func->rets.empty()) {
@@ -46,7 +44,7 @@ class Inliner : public BasicStmtVisitor {
       // Use a local variable to store the return value
       auto *return_address = inlined_ir->as<Block>()->insert(
           Stmt::make<AllocaStmt>(func->rets[0].dt), /*location=*/0);
-      irpass::replace_statements_with(
+      irpass::replace_and_insert_statements(
           inlined_ir.get(),
           /*filter=*/[&](Stmt *s) { return s->is<KernelReturnStmt>(); },
           /*generator=*/

taichi/transforms/replace_statements.cpp

@@ -0,0 +1,30 @@
+#include "taichi/ir/transforms.h"
+
+TLANG_NAMESPACE_BEGIN
+
+namespace irpass {
+
+bool replace_and_insert_statements(
+    IRNode *root,
+    std::function<bool(Stmt *)> filter,
+    std::function<std::unique_ptr<Stmt>(Stmt *)> generator) {
+  return transform_statements(root, std::move(filter),
+                              [&](Stmt *stmt, DelayedIRModifier *modifier) {
+                                modifier->replace_with(stmt, generator(stmt));
+                              });
+}
+
+bool replace_statements(IRNode *root,
+                        std::function<bool(Stmt *)> filter,
+                        std::function<Stmt *(Stmt *)> finder) {
+  return transform_statements(
+      root, std::move(filter), [&](Stmt *stmt, DelayedIRModifier *modifier) {
+        auto existing_new_stmt = finder(stmt);
+        irpass::replace_all_usages_with(root, stmt, existing_new_stmt);
+        modifier->erase(stmt);
+      });
+}
+
+}  // namespace irpass
+
+TLANG_NAMESPACE_END

taichi/transforms/transform_statements.cpp

@@ -0,0 +1,61 @@
+#include "taichi/ir/ir.h"
+#include "taichi/ir/statements.h"
+#include "taichi/ir/transforms.h"
+#include "taichi/ir/visitors.h"
+
+TLANG_NAMESPACE_BEGIN
+
+// Transform each filtered statement
+class StatementsTransformer : public BasicStmtVisitor {
+ public:
+  using BasicStmtVisitor::visit;
+
+  StatementsTransformer(
+      std::function<bool(Stmt *)> filter,
+      std::function<void(Stmt *, DelayedIRModifier *)> transformer)
+      : filter_(std::move(filter)), transformer_(std::move(transformer)) {
+    allow_undefined_visitor = true;
+    invoke_default_visitor = true;
+  }
+
+  void maybe_transform(Stmt *stmt) {
+    if (filter_(stmt)) {
+      transformer_(stmt, &modifier_);
+    }
+  }
+
+  void preprocess_container_stmt(Stmt *stmt) override {
+    maybe_transform(stmt);
+  }
+
+  void visit(Stmt *stmt) override {
+    maybe_transform(stmt);
+  }
+
+  static bool run(IRNode *root,
+                  std::function<bool(Stmt *)> filter,
+                  std::function<void(Stmt *, DelayedIRModifier *)> replacer) {
+    StatementsTransformer transformer(std::move(filter), std::move(replacer));
+    root->accept(&transformer);
+    return transformer.modifier_.modify_ir();
+  }
+
+ private:
+  std::function<bool(Stmt *)> filter_;
+  std::function<void(Stmt *, DelayedIRModifier *)> transformer_;
+  DelayedIRModifier modifier_;
+};
+
+namespace irpass {
+
+bool transform_statements(
+    IRNode *root,
+    std::function<bool(Stmt *)> filter,
+    std::function<void(Stmt *, DelayedIRModifier *)> transformer) {
+  return StatementsTransformer::run(root, std::move(filter),
+                                    std::move(transformer));
+}
+
+}  // namespace irpass
+
+TLANG_NAMESPACE_END