sketch out a new early cse pass. No functionality yet.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122713 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 63 insertions, 0 deletions

diff --git a/lib/Transforms/Scalar/EarlyCSE.cpp b/lib/Transforms/Scalar/EarlyCSE.cpp
new file mode 100644
index 0000000000..4445404f6c
--- /dev/null
+++ b/lib/Transforms/Scalar/EarlyCSE.cpp
@@ -0,0 +1,62 @@
+//===- EarlyCSE.cpp - Simple and fast CSE pass ----------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass performs a simple dominator tree walk that eliminates trivially
+// redundant instructions.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "early-cse"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Analysis/Dominators.h"
+#include "llvm/Pass.h"
+using namespace llvm;
+
+namespace {
+/// EarlyCSE - This pass does a simple depth-first walk over the dominator
+/// tree, eliminating trivially redundant instructions and using instsimplify
+/// to canonicalize things as it goes.  It is intended to be fast and catch
+/// obvious cases so that instcombine and other passes are more effective.  It
+/// is expected that a later pass of GVN will catch the interesting/hard
+/// cases.
+class EarlyCSE : public FunctionPass {
+public:
+  static char ID;
+  explicit EarlyCSE()
+      : FunctionPass(ID) {
+    initializeEarlyCSEPass(*PassRegistry::getPassRegistry());
+  }
+
+  bool runOnFunction(Function &F);
+
+private:
+  // This transformation requires dominator postdominator info
+  virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+    AU.addRequired<DominatorTree>();
+    AU.setPreservesCFG();
+  }
+};
+}
+
+char EarlyCSE::ID = 0;
+
+// createEarlyCSEPass - The public interface to this file.
+FunctionPass *llvm::createEarlyCSEPass() {
+  return new EarlyCSE();
+}
+
+INITIALIZE_PASS_BEGIN(EarlyCSE, "early-cse", "Early CSE", false, false)
+INITIALIZE_PASS_DEPENDENCY(DominatorTree)
+INITIALIZE_PASS_END(EarlyCSE, "early-cse", "Early CSE", false, false)
+
+bool EarlyCSE::runOnFunction(Function &F) {
+  DominatorTree &DT = getAnalysis<DominatorTree>();
+  (void)DT;
+  return false;
+}
diff --git a/lib/Transforms/Scalar/Scalar.cpp b/lib/Transforms/Scalar/Scalar.cpp
index 0eaf2895df..27c11186d6 100644
--- a/lib/Transforms/Scalar/Scalar.cpp
+++ b/lib/Transforms/Scalar/Scalar.cpp
@@ -36,6 +36,7 @@ void llvm::initializeScalarOpts(PassRegistry &Registry) {
   initializeDSEPass(Registry);
   initializeGEPSplitterPass(Registry);
   initializeGVNPass(Registry);
+  initializeEarlyCSEPass(Registry);
   initializeIndVarSimplifyPass(Registry);
   initializeJumpThreadingPass(Registry);
   initializeLICMPass(Registry);