1 files changed, 89 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/Scalar/FlattenCFGPass.cpp b/llvm/lib/Transforms/Scalar/FlattenCFGPass.cpp
new file mode 100644
index 000000000000..e6abf1ceb026
--- /dev/null
+++ b/llvm/lib/Transforms/Scalar/FlattenCFGPass.cpp
@@ -0,0 +1,89 @@
+//===- FlattenCFGPass.cpp - CFG Flatten Pass ----------------------===//
+//
+// 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 flattening of CFG.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/IR/CFG.h"
+#include "llvm/IR/ValueHandle.h"
+#include "llvm/Pass.h"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/Local.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "flattencfg"
+
+namespace {
+struct FlattenCFGPass : public FunctionPass {
+  static char ID; // Pass identification, replacement for typeid
+public:
+  FlattenCFGPass() : FunctionPass(ID) {
+    initializeFlattenCFGPassPass(*PassRegistry::getPassRegistry());
+  }
+  bool runOnFunction(Function &F) override;
+
+  void getAnalysisUsage(AnalysisUsage &AU) const override {
+    AU.addRequired<AAResultsWrapperPass>();
+  }
+
+private:
+  AliasAnalysis *AA;
+};
+}
+
+char FlattenCFGPass::ID = 0;
+INITIALIZE_PASS_BEGIN(FlattenCFGPass, "flattencfg", "Flatten the CFG", false,
+                      false)
+INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
+INITIALIZE_PASS_END(FlattenCFGPass, "flattencfg", "Flatten the CFG", false,
+                    false)
+
+// Public interface to the FlattenCFG pass
+FunctionPass *llvm::createFlattenCFGPass() { return new FlattenCFGPass(); }
+
+/// iterativelyFlattenCFG - Call FlattenCFG on all the blocks in the function,
+/// iterating until no more changes are made.
+static bool iterativelyFlattenCFG(Function &F, AliasAnalysis *AA) {
+  bool Changed = false;
+  bool LocalChange = true;
+
+  // Use block handles instead of iterating over function blocks directly
+  // to avoid using iterators invalidated by erasing blocks.
+  std::vector<WeakVH> Blocks;
+  Blocks.reserve(F.size());
+  for (auto &BB : F)
+    Blocks.push_back(&BB);
+
+  while (LocalChange) {
+    LocalChange = false;
+
+    // Loop over all of the basic blocks and try to flatten them.
+    for (WeakVH &BlockHandle : Blocks) {
+      // Skip blocks erased by FlattenCFG.
+      if (auto *BB = cast_or_null<BasicBlock>(BlockHandle))
+        if (FlattenCFG(BB, AA))
+          LocalChange = true;
+    }
+    Changed |= LocalChange;
+  }
+  return Changed;
+}
+
+bool FlattenCFGPass::runOnFunction(Function &F) {
+  AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
+  bool EverChanged = false;
+  // iterativelyFlattenCFG can make some blocks dead.
+  while (iterativelyFlattenCFG(F, AA)) {
+    removeUnreachableBlocks(F);
+    EverChanged = true;
+  }
+  return EverChanged;
+}