[WIP] Port dead store elimination pass from #3858

scripts/fuzz_opt.py

@@ -2430,6 +2430,7 @@ def write_commands(commands, filename):
     ("--remove-unused-names", "--heap2local",),
     ("--heap-store-optimization",),
     ("--generate-stack-ir",),
+    ("--ldse",),
     ("--licm",),
     ("--local-subtyping",),
     ("--memory-packing",),

src/ir/replacer.h

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2021 WebAssembly Community Group participants
+ *
+ * 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 wasm_ir_replacer_h
+#define wasm_ir_replacer_h
+
+#include <wasm-traversal.h>
+#include <wasm.h>
+
+namespace wasm {
+
+// A map of replacements to perform on expressions. After filling the map,
+// simply do a walk(..) and they will be replaced.
+//
+// This is useful for a general replacement of expressions. Some passes can
+// store pointers to expressions and update only those, but then there is the
+// nesting problem,
+//
+//  (foo
+//   (bar
+//    (baz
+//
+// If we replace bar with something then the pointer to baz may change. Doing
+// the replacements in the order of a walk, as is done here, is always safe.
+struct ExpressionReplacer
+  : PostWalker<ExpressionReplacer,
+               UnifiedExpressionVisitor<ExpressionReplacer>> {
+  std::unordered_map<Expression*, Expression*> replacements;
+
+  void visitExpression(Expression* curr) {
+    auto iter = replacements.find(curr);
+    if (iter != replacements.end()) {
+      replaceCurrent(iter->second);
+    }
+  }
+};
+
+} // namespace wasm
+
+#endif // wasm_ir_replacer_h

src/passes/CMakeLists.txt

@@ -30,6 +30,7 @@ set(passes_SOURCES
   DeadArgumentElimination.cpp
   DeadArgumentElimination2.cpp
   DeadCodeElimination.cpp
+  DeadStoreElimination.cpp
   DeAlign.cpp
   DebugLocationPropagation.cpp
   DeNaN.cpp