1 files changed, 120 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/Scalar/ConstantProp.cpp b/llvm/lib/Transforms/Scalar/ConstantProp.cpp
new file mode 100644
index 000000000000..e9e6afe3fdd4
--- /dev/null
+++ b/llvm/lib/Transforms/Scalar/ConstantProp.cpp
@@ -0,0 +1,120 @@
+//===- ConstantProp.cpp - Code to perform Simple Constant Propagation -----===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// 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 run a DIE pass sometime after running this pass.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/ConstantFolding.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/IR/Constant.h"
+#include "llvm/IR/InstIterator.h"
+#include "llvm/IR/Instruction.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/DebugCounter.h"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/Local.h"
+using namespace llvm;
+
+#define DEBUG_TYPE "constprop"
+
+STATISTIC(NumInstKilled, "Number of instructions killed");
+DEBUG_COUNTER(CPCounter, "constprop-transform",
+              "Controls which instructions are killed");
+
+namespace {
+  struct ConstantPropagation : public FunctionPass {
+    static char ID; // Pass identification, replacement for typeid
+    ConstantPropagation() : FunctionPass(ID) {
+      initializeConstantPropagationPass(*PassRegistry::getPassRegistry());
+    }
+
+    bool runOnFunction(Function &F) override;
+
+    void getAnalysisUsage(AnalysisUsage &AU) const override {
+      AU.setPreservesCFG();
+      AU.addRequired<TargetLibraryInfoWrapperPass>();
+    }
+  };
+}
+
+char ConstantPropagation::ID = 0;
+INITIALIZE_PASS_BEGIN(ConstantPropagation, "constprop",
+                "Simple constant propagation", false, false)
+INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
+INITIALIZE_PASS_END(ConstantPropagation, "constprop",
+                "Simple constant propagation", false, false)
+
+FunctionPass *llvm::createConstantPropagationPass() {
+  return new ConstantPropagation();
+}
+
+bool ConstantPropagation::runOnFunction(Function &F) {
+  if (skipFunction(F))
+    return false;
+
+  // Initialize the worklist to all of the instructions ready to process...
+  SmallPtrSet<Instruction *, 16> WorkList;
+  // The SmallVector of WorkList ensures that we do iteration at stable order.
+  // We use two containers rather than one SetVector, since remove is
+  // linear-time, and we don't care enough to remove from Vec.
+  SmallVector<Instruction *, 16> WorkListVec;
+  for (Instruction &I : instructions(&F)) {
+    WorkList.insert(&I);
+    WorkListVec.push_back(&I);
+  }
+
+  bool Changed = false;
+  const DataLayout &DL = F.getParent()->getDataLayout();
+  TargetLibraryInfo *TLI =
+      &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
+
+  while (!WorkList.empty()) {
+    SmallVector<Instruction*, 16> NewWorkListVec;
+    for (auto *I : WorkListVec) {
+      WorkList.erase(I); // Remove element from the worklist...
+
+      if (!I->use_empty()) // Don't muck with dead instructions...
+        if (Constant *C = ConstantFoldInstruction(I, DL, TLI)) {
+          if (!DebugCounter::shouldExecute(CPCounter))
+            continue;
+
+          // Add all of the users of this instruction to the worklist, they might
+          // be constant propagatable now...
+          for (User *U : I->users()) {
+            // If user not in the set, then add it to the vector.
+            if (WorkList.insert(cast<Instruction>(U)).second)
+              NewWorkListVec.push_back(cast<Instruction>(U));
+          }
+
+          // Replace all of the uses of a variable with uses of the constant.
+          I->replaceAllUsesWith(C);
+
+          if (isInstructionTriviallyDead(I, TLI)) {
+            I->eraseFromParent();
+            ++NumInstKilled;
+          }
+
+          // We made a change to the function...
+          Changed = true;
+        }
+    }
+    WorkListVec = std::move(NewWorkListVec);
+  }
+  return Changed;
+}