Add transform::Simplify

Performs basic peephole optimizations on the AST.

Use in transform::Hlsl.

Required to have the DecomposeStorageAccess transform operate correctly with the output of InlinePointerLets transform, specifically when declaring `let` pointer expressions to storage buffers.

Fixed: tint:221
Fixed: tint:492
Fixed: tint:829
Change-Id: I536390921a6492378104e9c3c100d9e761294a27
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/51921
Commit-Queue: Ben Clayton <bclayton@chromium.org>
Reviewed-by: David Neto <dneto@google.com>

src/BUILD.gn

@@ -519,6 +519,8 @@ libtint_source_set("libtint_core_all_src") {
     "transform/manager.h",
     "transform/renamer.cc",
     "transform/renamer.h",
+    "transform/simplify.cc",
+    "transform/simplify.h",
     "transform/single_entry_point.cc",
     "transform/single_entry_point.h",
     "transform/transform.cc",

src/CMakeLists.txt

@@ -282,6 +282,8 @@ set(TINT_LIB_SRCS
   transform/manager.h
   transform/renamer.cc
   transform/renamer.h
+  transform/simplify.cc
+  transform/simplify.h
   transform/single_entry_point.cc
   transform/single_entry_point.h
   transform/transform.cc
@@ -810,7 +812,8 @@ if(${TINT_BUILD_TESTS})
       transform/first_index_offset_test.cc
       transform/inline_pointer_lets_test.cc
       transform/renamer_test.cc
-      transform/single_entry_point.cc
+      transform/simplify_test.cc
+      transform/single_entry_point_test.cc
       transform/test_helper.h
       transform/var_for_dynamic_index_test.cc
       transform/vertex_pulling_test.cc

src/transform/hlsl.cc

@@ -29,6 +29,7 @@
 #include "src/transform/external_texture_transform.h"
 #include "src/transform/inline_pointer_lets.h"
 #include "src/transform/manager.h"
+#include "src/transform/simplify.h"
 
 namespace tint {
 namespace transform {
@@ -39,10 +40,16 @@ Hlsl::~Hlsl() = default;
 Output Hlsl::Run(const Program* in, const DataMap& data) {
   Manager manager;
   manager.Add<CanonicalizeEntryPointIO>();
+  manager.Add<InlinePointerLets>();
+  // Simplify cleans up messy `*(&(expr))` expressions from InlinePointerLets.
+  manager.Add<Simplify>();
+  // DecomposeStorageAccess must come after InlinePointerLets as we cannot take
+  // the address of calls to DecomposeStorageAccess::Intrinsic. Must also come
+  // after Simplify, as we need to fold away the address-of and defers of
+  // `*(&(intrinsic_load()))` expressions.
   manager.Add<DecomposeStorageAccess>();
   manager.Add<CalculateArrayLength>();
   manager.Add<ExternalTextureTransform>();
-  manager.Add<InlinePointerLets>();
   auto out = manager.Run(in, data);
   if (!out.program.IsValid()) {
     return out;

src/transform/simplify.cc

@@ -0,0 +1,63 @@
+// Copyright 2021 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "src/transform/simplify.h"
+
+#include <memory>
+#include <unordered_map>
+#include <utility>
+
+#include "src/program_builder.h"
+#include "src/sem/block_statement.h"
+#include "src/sem/function.h"
+#include "src/sem/statement.h"
+#include "src/sem/variable.h"
+#include "src/utils/scoped_assignment.h"
+
+namespace tint {
+namespace transform {
+
+Simplify::Simplify() = default;
+
+Simplify::~Simplify() = default;
+
+Output Simplify::Run(const Program* in, const DataMap&) {
+  ProgramBuilder out;
+  CloneContext ctx(&out, in);
+
+  ctx.ReplaceAll([&](ast::Expression* expr) -> ast::Expression* {
+    if (auto* outer = expr->As<ast::UnaryOpExpression>()) {
+      if (auto* inner = outer->expr()->As<ast::UnaryOpExpression>()) {
+        if (outer->op() == ast::UnaryOp::kAddressOf &&
+            inner->op() == ast::UnaryOp::kIndirection) {
+          // &(*(expr)) => expr
+          return ctx.Clone(inner->expr());
+        }
+        if (outer->op() == ast::UnaryOp::kIndirection &&
+            inner->op() == ast::UnaryOp::kAddressOf) {
+          // *(&(expr)) => expr
+          return ctx.Clone(inner->expr());
+        }
+      }
+    }
+    return nullptr;
+  });
+
+  ctx.Clone();
+
+  return Output(Program(std::move(out)));
+}
+
+}  // namespace transform
+}  // namespace tint

src/transform/simplify.h

@@ -0,0 +1,49 @@
+// Copyright 2021 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef SRC_TRANSFORM_SIMPLIFY_H_
+#define SRC_TRANSFORM_SIMPLIFY_H_
+
+#include <string>
+#include <unordered_map>
+
+#include "src/transform/transform.h"
+
+namespace tint {
+namespace transform {
+
+/// Simplify is a peephole optimizer Transform that simplifies ASTs by removing
+/// unnecessary operations.
+/// Simplify currently optimizes the following:
+/// `&(*(expr))` => `expr`
+/// `*(&(expr))` => `expr`
+class Simplify : public Transform {
+ public:
+  /// Constructor
+  Simplify();
+
+  /// Destructor
+  ~Simplify() override;
+
+  /// Runs the transform on `program`, returning the transformation result.
+  /// @param program the source program to transform
+  /// @param data optional extra transform-specific input data
+  /// @returns the transformation result
+  Output Run(const Program* program, const DataMap& data = {}) override;
+};
+
+}  // namespace transform
+}  // namespace tint
+
+#endif  // SRC_TRANSFORM_SIMPLIFY_H_

src/transform/simplify_test.cc

@@ -0,0 +1,112 @@
+// Copyright 2021 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "src/transform/simplify.h"
+
+#include <memory>
+#include <utility>
+#include <vector>
+
+#include "src/transform/test_helper.h"
+
+namespace tint {
+namespace transform {
+namespace {
+
+using SimplifyTest = TransformTest;
+
+TEST_F(SimplifyTest, EmptyModule) {
+  auto* src = "";
+  auto* expect = "";
+
+  auto got = Run<Simplify>(src);
+
+  EXPECT_EQ(expect, str(got));
+}
+
+TEST_F(SimplifyTest, AddressOfDeref) {
+  auto* src = R"(
+fn f() {
+  var v : i32;
+  let p : ptr<function, i32> = &(v);
+  let x : ptr<function, i32> = &(*(p));
+  let y : ptr<function, i32> = &(*(&(*(p))));
+  let z : ptr<function, i32> = &(*(&(*(&(*(&(*(p))))))));
+}
+)";
+
+  auto* expect = R"(
+fn f() {
+  var v : i32;
+  let p : ptr<function, i32> = &(v);
+  let x : ptr<function, i32> = p;
+  let y : ptr<function, i32> = p;
+  let z : ptr<function, i32> = p;
+}
+)";
+
+  auto got = Run<Simplify>(src);
+
+  EXPECT_EQ(expect, str(got));
+}
+
+TEST_F(SimplifyTest, DerefAddressOf) {
+  auto* src = R"(
+fn f() {
+  var v : i32;
+  let x : i32 = *(&(v));
+  let y : i32 = *(&(*(&(v))));
+  let z : i32 = *(&(*(&(*(&(*(&(v))))))));
+}
+)";
+
+  auto* expect = R"(
+fn f() {
+  var v : i32;
+  let x : i32 = v;
+  let y : i32 = v;
+  let z : i32 = v;
+}
+)";
+
+  auto got = Run<Simplify>(src);
+
+  EXPECT_EQ(expect, str(got));
+}
+
+TEST_F(SimplifyTest, NoChange) {
+  auto* src = R"(
+fn f() {
+  var v : i32;
+  let p : ptr<function, i32> = &(v);
+  let x : i32 = *(p);
+}
+)";
+
+  auto* expect = R"(
+fn f() {
+  var v : i32;
+  let p : ptr<function, i32> = &(v);
+  let x : i32 = *(p);
+}
+)";
+
+  auto got = Run<Simplify>(src);
+
+  EXPECT_EQ(expect, str(got));
+}
+
+}  // namespace
+}  // namespace transform
+}  // namespace tint