-//===- SimplifyCFG.cpp - CFG Simplification Routines -------------*- C++ -*--=//
+//===- UnifyFunctionExitNodes.cpp - Make all functions have a single exit -===//
//
-// This file provides several routines that are useful for simplifying CFGs in
-// various ways...
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass is used to ensure that functions have at most one return
+// instruction in them. Additionally, it keeps track of which node is the new
+// exit node of the CFG. If there are no exit nodes in the CFG, the getExitNode
+// method will return a null pointer.
//
//===----------------------------------------------------------------------===//
-#include "llvm/Analysis/SimplifyCFG.h"
-#include "llvm/BasicBlock.h"
-#include "llvm/Method.h"
-#include "llvm/iTerminators.h"
-#include "llvm/iPHINode.h"
-#include "llvm/Type.h"
-using std::vector;
+#include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Type.h"
+#include "llvm/Transforms/Scalar.h"
+using namespace llvm;
+
+char UnifyFunctionExitNodes::ID = 0;
+INITIALIZE_PASS(UnifyFunctionExitNodes, "mergereturn",
+ "Unify function exit nodes", false, false)
+
+Pass *llvm::createUnifyFunctionExitNodesPass() {
+ return new UnifyFunctionExitNodes();
+}
+
+void UnifyFunctionExitNodes::getAnalysisUsage(AnalysisUsage &AU) const{
+ // We preserve the non-critical-edgeness property
+ AU.addPreservedID(BreakCriticalEdgesID);
+ // This is a cluster of orthogonal Transforms
+ AU.addPreservedID(LowerSwitchID);
+}
// UnifyAllExitNodes - Unify all exit nodes of the CFG by creating a new
// BasicBlock, and converting all returns to unconditional branches to this
// new basic block. The singular exit node is returned.
//
-// If there are no return stmts in the Method, a null pointer is returned.
+// If there are no return stmts in the Function, a null pointer is returned.
//
-BasicBlock *cfg::UnifyAllExitNodes(Method *M) {
- vector<BasicBlock*> ReturningBlocks;
-
- // Loop over all of the blocks in a method, tracking all of the blocks that
+bool UnifyFunctionExitNodes::runOnFunction(Function &F) {
+ // Loop over all of the blocks in a function, tracking all of the blocks that
// return.
//
- for(Method::iterator I = M->begin(), E = M->end(); I != E; ++I)
- if ((*I)->getTerminator()->getOpcode() == Instruction::Ret)
- ReturningBlocks.push_back(*I);
+ std::vector<BasicBlock*> ReturningBlocks;
+ std::vector<BasicBlock*> UnreachableBlocks;
+ for (BasicBlock &I : F)
+ if (isa<ReturnInst>(I.getTerminator()))
+ ReturningBlocks.push_back(&I);
+ else if (isa<UnreachableInst>(I.getTerminator()))
+ UnreachableBlocks.push_back(&I);
- if (ReturningBlocks.size() == 0)
- return 0; // No blocks return
- else if (ReturningBlocks.size() == 1)
- return ReturningBlocks.front(); // Already has a single return block
+ // Then unreachable blocks.
+ if (UnreachableBlocks.empty()) {
+ UnreachableBlock = nullptr;
+ } else if (UnreachableBlocks.size() == 1) {
+ UnreachableBlock = UnreachableBlocks.front();
+ } else {
+ UnreachableBlock = BasicBlock::Create(F.getContext(),
+ "UnifiedUnreachableBlock", &F);
+ new UnreachableInst(F.getContext(), UnreachableBlock);
- // Otherwise, we need to insert a new basic block into the method, add a PHI
- // node (if the function returns a value), and convert all of the return
- // instructions into unconditional branches.
- //
- BasicBlock *NewRetBlock = new BasicBlock("", M);
+ for (std::vector<BasicBlock*>::iterator I = UnreachableBlocks.begin(),
+ E = UnreachableBlocks.end(); I != E; ++I) {
+ BasicBlock *BB = *I;
+ BB->getInstList().pop_back(); // Remove the unreachable inst.
+ BranchInst::Create(UnreachableBlock, BB);
+ }
+ }
- if (M->getReturnType() != Type::VoidTy) {
- // If the method doesn't return void... add a PHI node to the block...
- PHINode *PN = new PHINode(M->getReturnType());
- NewRetBlock->getInstList().push_back(PN);
+ // Now handle return blocks.
+ if (ReturningBlocks.empty()) {
+ ReturnBlock = nullptr;
+ return false; // No blocks return
+ } else if (ReturningBlocks.size() == 1) {
+ ReturnBlock = ReturningBlocks.front(); // Already has a single return block
+ return false;
+ }
- // Add an incoming element to the PHI node for every return instruction that
- // is merging into this new block...
- for (vector<BasicBlock*>::iterator I = ReturningBlocks.begin(),
- E = ReturningBlocks.end(); I != E; ++I)
- PN->addIncoming((*I)->getTerminator()->getOperand(0), *I);
+ // Otherwise, we need to insert a new basic block into the function, add a PHI
+ // nodes (if the function returns values), and convert all of the return
+ // instructions into unconditional branches.
+ //
+ BasicBlock *NewRetBlock = BasicBlock::Create(F.getContext(),
+ "UnifiedReturnBlock", &F);
- // Add a return instruction to return the result of the PHI node...
- NewRetBlock->getInstList().push_back(new ReturnInst(PN));
+ PHINode *PN = nullptr;
+ if (F.getReturnType()->isVoidTy()) {
+ ReturnInst::Create(F.getContext(), nullptr, NewRetBlock);
} else {
- // If it returns void, just add a return void instruction to the block
- NewRetBlock->getInstList().push_back(new ReturnInst());
+ // If the function doesn't return void... add a PHI node to the block...
+ PN = PHINode::Create(F.getReturnType(), ReturningBlocks.size(),
+ "UnifiedRetVal");
+ NewRetBlock->getInstList().push_back(PN);
+ ReturnInst::Create(F.getContext(), PN, NewRetBlock);
}
// Loop over all of the blocks, replacing the return instruction with an
// unconditional branch.
//
- for (vector<BasicBlock*>::iterator I = ReturningBlocks.begin(),
- E = ReturningBlocks.end(); I != E; ++I) {
- delete (*I)->getInstList().pop_back(); // Remove the return insn
- (*I)->getInstList().push_back(new BranchInst(NewRetBlock));
+ for (std::vector<BasicBlock*>::iterator I = ReturningBlocks.begin(),
+ E = ReturningBlocks.end(); I != E; ++I) {
+ BasicBlock *BB = *I;
+
+ // Add an incoming element to the PHI node for every return instruction that
+ // is merging into this new block...
+ if (PN)
+ PN->addIncoming(BB->getTerminator()->getOperand(0), BB);
+
+ BB->getInstList().pop_back(); // Remove the return insn
+ BranchInst::Create(NewRetBlock, BB);
}
- return NewRetBlock;
+ ReturnBlock = NewRetBlock;
+ return true;
}
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