1 files changed, 80 insertions, 0 deletions
diff --git a/src/passes/MemoryPacking.cpp b/src/passes/MemoryPacking.cpp
new file mode 100644
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--- /dev/null
+++ b/src/passes/MemoryPacking.cpp
@@ -0,0 +1,80 @@
+/*
+ * Copyright 2016 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.
+ */
+
+#include <wasm.h>
+#include <pass.h>
+#include <wasm-builder.h>
+
+namespace wasm {
+
+// Adding segments adds overhead, this is a rough estimate
+const Index OVERHEAD = 8;
+
+struct MemoryPacking : public Pass {
+  void run(PassRunner* runner, Module* module) override {
+    if (!module->memory.exists) return;
+    std::vector<Memory::Segment> packed;
+    for (auto& segment : module->memory.segments) {
+      // skip final zeros
+      while (segment.data.size() > 0 && segment.data.back() == 0) {
+        segment.data.pop_back();
+      }
+      // we can only handle a constant offset for splitting
+      if (auto* offset = segment.offset->dynCast<Const>()) {
+        // Find runs of zeros, and split
+        auto& data = segment.data;
+        auto base = offset->value.geti32();
+        Index start = 0;
+        // create new segments
+        while (start < data.size()) {
+          // skip initial zeros
+          while (start < data.size() && data[start] == 0) {
+            start++;
+          }
+          Index end = start; // end of data-containing part
+          Index next = end; // after zeros we can skip. preserves next >= end
+          while (next < data.size() && (next - end < OVERHEAD)) {
+            if (data[end] != 0) {
+              end++;
+              next = end; // we can try to skip zeros from here
+            } else {
+              // end is on a zero, we are looking to skip
+              if (data[next] != 0) {
+                end = next; // we must extend the segment, including some zeros
+              } else {
+                next++;
+              }
+            }
+          }
+          if (end != start) {
+            packed.emplace_back(Builder(*module).makeConst(Literal(int32_t(base + start))), &data[start], end - start);
+          }
+          start = next;
+        }
+      } else {
+        packed.push_back(segment);
+      }
+    }
+    module->memory.segments.swap(packed);
+  }
+};
+
+Pass *createMemoryPackingPass() {
+  return new MemoryPacking();
+}
+
+} // namespace wasm
+