6 files changed, 128 insertions, 0 deletions
diff --git a/src/asmjs/shared-constants.cpp b/src/asmjs/shared-constants.cpp
index d704c8009..02e80d36b 100644
--- a/src/asmjs/shared-constants.cpp
+++ b/src/asmjs/shared-constants.cpp
@@ -55,6 +55,7 @@ cashew::IString GLOBAL("global"),
                 USE_ASM("use asm"),
                 BUFFER("buffer"),
                 ENV("env"),
+                INSTRUMENT("instrument"),
                 MATH_IMUL("Math_imul"),
                 MATH_CLZ32("Math_clz32"),
                 MATH_CTZ32("Math_ctz32"),
diff --git a/src/asmjs/shared-constants.h b/src/asmjs/shared-constants.h
index 7b48c3df5..f13023778 100644
--- a/src/asmjs/shared-constants.h
+++ b/src/asmjs/shared-constants.h
@@ -58,6 +58,7 @@ extern cashew::IString GLOBAL,
                 USE_ASM,
                 BUFFER,
                 ENV,
+                INSTRUMENT,
                 MATH_IMUL,
                 MATH_CLZ32,
                 MATH_CTZ32,
diff --git a/src/passes/CMakeLists.txt b/src/passes/CMakeLists.txt
index 75e634c16..637f40d94 100644
--- a/src/passes/CMakeLists.txt
+++ b/src/passes/CMakeLists.txt
@@ -9,6 +9,7 @@ SET(passes_SOURCES
   LegalizeJSInterface.cpp
   LocalCSE.cpp
   LogExecution.cpp
+  InstrumentMemory.cpp
   MemoryPacking.cpp
   MergeBlocks.cpp
   Metrics.cpp
diff --git a/src/passes/InstrumentMemory.cpp b/src/passes/InstrumentMemory.cpp
new file mode 100644
index 000000000..536031064
--- /dev/null
+++ b/src/passes/InstrumentMemory.cpp
@@ -0,0 +1,123 @@
+/*
+ * Copyright 2017 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.
+ */
+
+//
+// Instruments the build with code to intercept all memory reads and writes.
+// This can be useful in building tools that analyze memory access behaviour.
+//
+// The instrumentation is performed by calling an FFI with an ID for each
+// memory access site. Load / store IDs share the same index space. The
+// instrumentation wraps the evaluation of the address operand, therefore
+// it executes before the load / store is executed. Note that Instrumentation
+// code must return tha address argument.
+//
+// Loads: load(id, bytes, offset, address) => address
+//
+//  Before:
+//   (i32.load8_s align=1 offset=2 (i32.const 3))
+//
+//  After:
+//   (i32.load8_s align=1 offset=2
+//    (call $load
+//     (i32.const n) // ID
+//     (i32.const 1) // bytes
+//     (i32.const 2) // offset
+//     (i32.const 3) // address
+//    )
+//   )
+//
+// Stores: store(id, bytes, offset, address) => address
+//
+//  Before:
+//   (i32.store8 align=1 offset=2 (i32.const 3) (i32.const 4))
+//
+//  After:
+//   (i32.store16 align=1 offset=2
+//    (call $store
+//     (i32.const n) // ID
+//     (i32.const 1) // bytes
+//     (i32.const 2) // offset
+//     (i32.const 3) // address
+//    )
+//    (i32.const 4)
+//   )
+
+#include <wasm.h>
+#include <wasm-builder.h>
+#include <pass.h>
+#include "shared-constants.h"
+#include "asmjs/shared-constants.h"
+#include "asm_v_wasm.h"
+
+namespace wasm {
+
+Name load("load");
+Name store("store");
+
+struct InstrumentMemory : public WalkerPass<PostWalker<InstrumentMemory>> {
+  void visitLoad(Load* curr) {
+    makeLoadCall(curr);
+  }
+  void visitStore(Store* curr) {
+    makeStoreCall(curr);
+  }
+  void addImport(Module *curr, Name name, std::string sig) {
+    auto import = new Import;
+    import->name = name;
+    import->module = INSTRUMENT;
+    import->base = name;
+    import->functionType = ensureFunctionType(sig, curr)->name;
+    import->kind = ExternalKind::Function;
+    curr->addImport(import);
+  }
+
+  void visitModule(Module *curr) {
+    addImport(curr, load,  "iiiii");
+    addImport(curr, store,  "iiiii");
+  }
+
+private:
+  std::atomic<Index> id;
+  Expression* makeLoadCall(Load* curr) {
+    Builder builder(*getModule());
+    curr->ptr = builder.makeCallImport(load,
+      { builder.makeConst(Literal(int32_t(id.fetch_add(1)))),
+        builder.makeConst(Literal(int32_t(curr->bytes))),
+        builder.makeConst(Literal(int32_t(curr->offset.addr))),
+        curr->ptr},
+      i32
+    );
+    return curr;
+  }
+
+  Expression* makeStoreCall(Store* curr) {
+    Builder builder(*getModule());
+    curr->ptr = builder.makeCallImport(store,
+      { builder.makeConst(Literal(int32_t(id.fetch_add(1)))),
+        builder.makeConst(Literal(int32_t(curr->bytes))),
+        builder.makeConst(Literal(int32_t(curr->offset.addr))),
+        curr->ptr },
+      i32
+    );
+    return curr;
+  }
+};
+
+Pass *createInstrumentMemoryPass() {
+  return new InstrumentMemory();
+}
+
+} // namespace wasm
diff --git a/src/passes/pass.cpp b/src/passes/pass.cpp
index 8da42f9cd..51e76cdf7 100644
--- a/src/passes/pass.cpp
+++ b/src/passes/pass.cpp
@@ -74,6 +74,7 @@ void PassRegistry::registerPasses() {
   registerPass("legalize-js-interface", "legalizes i64 types on the import/export boundary", createLegalizeJSInterfacePass);
   registerPass("local-cse", "common subexpression elimination inside basic blocks", createLocalCSEPass);
   registerPass("log-execution", "instrument the build with logging of where execution goes", createLogExecutionPass);
+  registerPass("instrument-memory", "instrument the build with code to intercept all loads and stores", createInstrumentMemoryPass);
   registerPass("memory-packing", "packs memory into separate segments, skipping zeros", createMemoryPackingPass);
   registerPass("merge-blocks", "merges blocks to their parents", createMergeBlocksPass);
   registerPass("metrics", "reports metrics", createMetricsPass);
diff --git a/src/passes/passes.h b/src/passes/passes.h
index f8156d4fe..709a903f1 100644
--- a/src/passes/passes.h
+++ b/src/passes/passes.h
@@ -33,6 +33,7 @@ Pass *createInliningPass();
 Pass *createLegalizeJSInterfacePass();
 Pass *createLocalCSEPass();
 Pass *createLogExecutionPass();
+Pass *createInstrumentMemoryPass();
 Pass *createMemoryPackingPass();
 Pass *createMergeBlocksPass();
 Pass *createMinifiedPrinterPass();