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
diff --git a/lib/Transforms/Scalar/EarlyCSE.cpp b/lib/Transforms/Scalar/EarlyCSE.cpp
new file mode 100644
index 0000000..4445404
--- /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;
+}