1 files changed, 83 insertions, 0 deletions
diff --git a/lib/Transforms/Scalar/ConstantProp.cpp b/lib/Transforms/Scalar/ConstantProp.cpp
new file mode 100644
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+++ b/lib/Transforms/Scalar/ConstantProp.cpp
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+//===- ConstantProp.cpp - Code to perform Simple Constant Propagation -----===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by the LLVM research group and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements constant propagation and merging:
+//
+// Specifically, this:
+//   * Converts instructions like "add int 1, 2" into 3
+//
+// Notice that:
+//   * This pass has a habit of making definitions be dead.  It is a good idea
+//     to to run a DIE pass sometime after running this pass.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Constant.h"
+#include "llvm/Instruction.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/InstIterator.h"
+#include "llvm/ADT/Statistic.h"
+#include <set>
+using namespace llvm;
+
+namespace {
+  Statistic<> NumInstKilled("constprop", "Number of instructions killed");
+
+  struct ConstantPropagation : public FunctionPass {
+    bool runOnFunction(Function &F);
+
+    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+      AU.setPreservesCFG();
+    }
+  };
+
+  RegisterOpt<ConstantPropagation> X("constprop","Simple constant propagation");
+}
+
+FunctionPass *llvm::createConstantPropagationPass() {
+  return new ConstantPropagation();
+}
+
+
+bool ConstantPropagation::runOnFunction(Function &F) {
+  // Initialize the worklist to all of the instructions ready to process...
+  std::set<Instruction*> WorkList;
+  for(inst_iterator i = inst_begin(F), e = inst_end(F); i != e; ++i) {
+      WorkList.insert(&*i);
+  }
+  bool Changed = false;
+
+  while (!WorkList.empty()) {
+    Instruction *I = *WorkList.begin();
+    WorkList.erase(WorkList.begin());    // Get an element from the worklist...
+
+    if (!I->use_empty())                 // Don't muck with dead instructions...
+      if (Constant *C = ConstantFoldInstruction(I)) {
+        // Add all of the users of this instruction to the worklist, they might
+        // be constant propagatable now...
+        for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
+             UI != UE; ++UI)
+          WorkList.insert(cast<Instruction>(*UI));
+
+        // Replace all of the uses of a variable with uses of the constant.
+        I->replaceAllUsesWith(C);
+
+        // Remove the dead instruction.
+        WorkList.erase(I);
+        I->getParent()->getInstList().erase(I);
+
+        // We made a change to the function...
+        Changed = true;
+        ++NumInstKilled;
+      }
+  }
+  return Changed;
+}