Add method to unify all exit nodes of a method

llvm-svn: 143

llvm/lib/Transforms/Utils/UnifyFunctionExitNodes.cpp

@@ -0,0 +1,69 @@
+//===- SimplifyCFG.cpp - CFG Simplification Routines -------------*- C++ -*--=//
+//
+// This file provides several routines that are useful for simplifying CFGs in
+// various ways...
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/SimplifyCFG.h"
+#include "llvm/BasicBlock.h"
+#include "llvm/Method.h"
+#include "llvm/iTerminators.h"
+#include "llvm/iOther.h"
+#include "llvm/Type.h"
+
+// 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.
+//
+BasicBlock *cfg::UnifyAllExitNodes(Method *M) {
+  vector<BasicBlock*> ReturningBlocks;
+
+  // Loop over all of the blocks in a method, tracking all of the blocks that
+  // return.
+  //
+  for(Method::iterator I = M->begin(), E = M->end(); I != E; ++I)
+    if ((*I)->getTerminator()->getInstType() == Instruction::Ret)
+      ReturningBlocks.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
+
+  // 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);
+
+  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);
+
+    // 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);
+
+    // Add a return instruction to return the result of the PHI node...
+    NewRetBlock->getInstList().push_back(new ReturnInst(PN));
+  } else {
+    // If it returns void, just add a return void instruction to the block
+    NewRetBlock->getInstList().push_back(new ReturnInst());
+  }
+
+  // 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));
+  }
+  return NewRetBlock;
+}