Start sketching out the optimizer

external/CMakeLists.txt

@@ -18,7 +18,7 @@ ExternalProject_Add(llvm
                     GIT_SHALLOW
                       1
                     GIT_TAG
-                      b1e6cc762cd729de01f1b4f3c0f6d9a493635ae0
+                      release_50
                     CMAKE_ARGS
                       -DCMAKE_BUILD_TYPE=RelWithDebInfo
                       -DBUILD_SHARED_LIBS=NO

include/glow/Optimizer/Optimizer.h

@@ -0,0 +1,12 @@
+#ifndef GLOW_OPTIMIZER_OPTIMIZER_H
+#define GLOW_OPTIMIZER_OPTIMIZER_H
+
+namespace glow {
+
+class Module;
+
+void optimize(Module &M);
+
+} // namespace glow
+
+#endif // GLOW_OPTIMIZER_OPTIMIZER_H

src/glow/CMakeLists.txt

@@ -1,8 +1,9 @@
 
+add_subdirectory(IR)
 add_subdirectory(Importer)
 add_subdirectory(Interpreter)
-add_subdirectory(IR)
 add_subdirectory(Models)
 add_subdirectory(Network)
+add_subdirectory(Optimizer)
 add_subdirectory(Support)
 

src/glow/Optimizer/CMakeLists.txt

@@ -0,0 +1,8 @@
+
+add_library(Optimizer
+            Optimizer.cpp)
+
+target_link_libraries(Optimizer
+                      PRIVATE
+                        IR)
+

src/glow/Optimizer/Optimizer.cpp

@@ -0,0 +1,54 @@
+#include "glow/Optimizer/Optimizer.h"
+#include "glow/IR/IR.h"
+#include "glow/IR/Instrs.h"
+#include "glow/Support/Casting.h"
+
+#include <unordered_map>
+
+using namespace glow;
+
+/// Hoists Dealloc instructions right after their last use.
+static void hoistDealloc(Module &M) {
+  using iterator = Module::InstListTy::iterator;
+  // Maps activation instructions to their last non-dealloc user.
+  std::unordered_map<AllocActivationInst *, iterator> lastUser;
+  auto &instrs = M.getInstrs();
+
+  // Record the last use of each dealloc.
+  for (auto it = instrs.begin(), e = instrs.end(); it != e; ++it) {
+    if (isa<DeallocActivationInst>(*it))
+      continue;
+
+    for (int i = 0, e = (*it)->getNumOperands(); i < e; i++) {
+      auto op = (*it)->getOperand(i).first;
+      if (auto alloc = dyn_cast<AllocActivationInst>(op)) {
+        lastUser[alloc] = it;
+      }
+    }
+  }
+
+  // Now that we've found the last user we can hoist the instruction.
+  for (auto it = instrs.begin(), e = instrs.end(); it != e; /* increment below */) {
+    iterator curr = it;
+    auto *da = dyn_cast<DeallocActivationInst>(*curr);
+    if (!da) {
+      ++it;
+      continue;
+    }
+
+    auto *alloc = cast<AllocActivationInst>(da->getOperand(0).first);
+
+    it = instrs.erase(curr);
+    auto &where = lastUser[alloc];
+    where++;
+    instrs.insert(where, da);
+  }
+}
+
+void glow::optimize(Module &M) {
+  M.verify();
+
+  hoistDealloc(M);
+
+  M.verify();
+}