Imported Upstream version 5.18.0.246

Former-commit-id: 0c7ce5b1a7851e13f22acfd379b7f9fb304e4833

external/llvm/lib/Transforms/Scalar/FlattenCFGPass.cpp

@@ -0,0 +1,80 @@
+//===- FlattenCFGPass.cpp - CFG Flatten Pass ----------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements flattening of CFG.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/IR/CFG.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;
+  while (LocalChange) {
+    LocalChange = false;
+
+    // Loop over all of the basic blocks and remove them if they are unneeded...
+    //
+    for (Function::iterator BBIt = F.begin(); BBIt != F.end();) {
+      if (FlattenCFG(&*BBIt++, 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;
+}