rename SimplifyCFG.cpp -> SimplifyCFGPass.cpp
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51130 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/SimplifyCFGPass.cpp b/lib/Transforms/Scalar/SimplifyCFGPass.cpp
new file mode 100644
index 0000000..2368328
--- /dev/null
+++ b/lib/Transforms/Scalar/SimplifyCFGPass.cpp
@@ -0,0 +1,231 @@
+//===- SimplifyCFGPass.cpp - CFG Simplification 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 dead code elimination and basic block merging, along
+// with a collection of other peephole control flow optimizations. For example:
+//
+// * Removes basic blocks with no predecessors.
+// * Merges a basic block into its predecessor if there is only one and the
+// predecessor only has one successor.
+// * Eliminates PHI nodes for basic blocks with a single predecessor.
+// * Eliminates a basic block that only contains an unconditional branch.
+// * Changes invoke instructions to nounwind functions to be calls.
+// * Change things like "if (x) if (y)" into "if (x&y)".
+// * etc..
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "simplifycfg"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Constants.h"
+#include "llvm/Instructions.h"
+#include "llvm/Module.h"
+#include "llvm/ParameterAttributes.h"
+#include "llvm/Support/CFG.h"
+#include "llvm/Support/Compiler.h"
+#include "llvm/Pass.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/Statistic.h"
+using namespace llvm;
+
+STATISTIC(NumSimpl, "Number of blocks simplified");
+
+namespace {
+ struct VISIBILITY_HIDDEN CFGSimplifyPass : public FunctionPass {
+ static char ID; // Pass identification, replacement for typeid
+ CFGSimplifyPass() : FunctionPass((intptr_t)&ID) {}
+
+ virtual bool runOnFunction(Function &F);
+ };
+}
+
+char CFGSimplifyPass::ID = 0;
+static RegisterPass<CFGSimplifyPass> X("simplifycfg", "Simplify the CFG");
+
+// Public interface to the CFGSimplification pass
+FunctionPass *llvm::createCFGSimplificationPass() {
+ return new CFGSimplifyPass();
+}
+
+/// ChangeToUnreachable - Insert an unreachable instruction before the specified
+/// instruction, making it and the rest of the code in the block dead.
+static void ChangeToUnreachable(Instruction *I) {
+ BasicBlock *BB = I->getParent();
+ // Loop over all of the successors, removing BB's entry from any PHI
+ // nodes.
+ for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
+ (*SI)->removePredecessor(BB);
+
+ new UnreachableInst(I);
+
+ // All instructions after this are dead.
+ BasicBlock::iterator BBI = I, BBE = BB->end();
+ while (BBI != BBE) {
+ if (!BBI->use_empty())
+ BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
+ BB->getInstList().erase(BBI++);
+ }
+}
+
+/// ChangeToCall - Convert the specified invoke into a normal call.
+static void ChangeToCall(InvokeInst *II) {
+ BasicBlock *BB = II->getParent();
+ SmallVector<Value*, 8> Args(II->op_begin()+3, II->op_end());
+ CallInst *NewCall = CallInst::Create(II->getCalledValue(), Args.begin(),
+ Args.end(), "", II);
+ NewCall->takeName(II);
+ NewCall->setCallingConv(II->getCallingConv());
+ NewCall->setParamAttrs(II->getParamAttrs());
+ II->replaceAllUsesWith(NewCall);
+
+ // Follow the call by a branch to the normal destination.
+ BranchInst::Create(II->getNormalDest(), II);
+
+ // Update PHI nodes in the unwind destination
+ II->getUnwindDest()->removePredecessor(BB);
+ BB->getInstList().erase(II);
+}
+
+static bool MarkAliveBlocks(BasicBlock *BB,
+ SmallPtrSet<BasicBlock*, 128> &Reachable) {
+
+ SmallVector<BasicBlock*, 128> Worklist;
+ Worklist.push_back(BB);
+ bool Changed = false;
+ while (!Worklist.empty()) {
+ BB = Worklist.back();
+ Worklist.pop_back();
+
+ if (!Reachable.insert(BB))
+ continue;
+
+ // Do a quick scan of the basic block, turning any obviously unreachable
+ // instructions into LLVM unreachable insts. The instruction combining pass
+ // canonicalizes unreachable insts into stores to null or undef.
+ for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E;++BBI){
+ if (CallInst *CI = dyn_cast<CallInst>(BBI)) {
+ if (CI->doesNotReturn()) {
+ // If we found a call to a no-return function, insert an unreachable
+ // instruction after it. Make sure there isn't *already* one there
+ // though.
+ ++BBI;
+ if (!isa<UnreachableInst>(BBI)) {
+ ChangeToUnreachable(BBI);
+ Changed = true;
+ }
+ break;
+ }
+ }
+
+ if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
+ if (isa<ConstantPointerNull>(SI->getOperand(1)) ||
+ isa<UndefValue>(SI->getOperand(1))) {
+ ChangeToUnreachable(SI);
+ Changed = true;
+ break;
+ }
+ }
+
+ // Turn invokes that call 'nounwind' functions into ordinary calls.
+ if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator()))
+ if (II->doesNotThrow()) {
+ ChangeToCall(II);
+ Changed = true;
+ }
+
+ Changed |= ConstantFoldTerminator(BB);
+ for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
+ Worklist.push_back(*SI);
+ }
+ return Changed;
+}
+
+/// RemoveUnreachableBlocks - Remove blocks that are not reachable, even if they
+/// are in a dead cycle. Return true if a change was made, false otherwise.
+static bool RemoveUnreachableBlocks(Function &F) {
+ SmallPtrSet<BasicBlock*, 128> Reachable;
+ bool Changed = MarkAliveBlocks(F.begin(), Reachable);
+
+ // If there are unreachable blocks in the CFG...
+ if (Reachable.size() == F.size())
+ return Changed;
+
+ assert(Reachable.size() < F.size());
+ NumSimpl += F.size()-Reachable.size();
+
+ // Loop over all of the basic blocks that are not reachable, dropping all of
+ // their internal references...
+ for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB) {
+ if (Reachable.count(BB))
+ continue;
+
+ for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
+ if (Reachable.count(*SI))
+ (*SI)->removePredecessor(BB);
+ BB->dropAllReferences();
+ }
+
+ for (Function::iterator I = ++F.begin(); I != F.end();)
+ if (!Reachable.count(I))
+ I = F.getBasicBlockList().erase(I);
+ else
+ ++I;
+
+ return true;
+}
+
+/// IterativeSimplifyCFG - Call SimplifyCFG on all the blocks in the function,
+/// iterating until no more changes are made.
+static bool IterativeSimplifyCFG(Function &F) {
+ bool Changed = false;
+ bool LocalChange = true;
+ while (LocalChange) {
+ LocalChange = false;
+
+ // Loop over all of the basic blocks (except the first one) and remove them
+ // if they are unneeded...
+ //
+ for (Function::iterator BBIt = ++F.begin(); BBIt != F.end(); ) {
+ if (SimplifyCFG(BBIt++)) {
+ LocalChange = true;
+ ++NumSimpl;
+ }
+ }
+ Changed |= LocalChange;
+ }
+ return Changed;
+}
+
+// It is possible that we may require multiple passes over the code to fully
+// simplify the CFG.
+//
+bool CFGSimplifyPass::runOnFunction(Function &F) {
+ bool EverChanged = RemoveUnreachableBlocks(F);
+ EverChanged |= IterativeSimplifyCFG(F);
+
+ // If neither pass changed anything, we're done.
+ if (!EverChanged) return false;
+
+ // IterativeSimplifyCFG can (rarely) make some loops dead. If this happens,
+ // RemoveUnreachableBlocks is needed to nuke them, which means we should
+ // iterate between the two optimizations. We structure the code like this to
+ // avoid reruning IterativeSimplifyCFG if the second pass of
+ // RemoveUnreachableBlocks doesn't do anything.
+ if (!RemoveUnreachableBlocks(F))
+ return true;
+
+ do {
+ EverChanged = IterativeSimplifyCFG(F);
+ EverChanged |= RemoveUnreachableBlocks(F);
+ } while (EverChanged);
+
+ return true;
+}