Add the majority of machine-level critical edge breaking pass. Most of this was written by Fernando, cleanup and updating to TOT by me.

This still needs a bit of work, particularly to handle jump tables properly.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@43885 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/BreakCriticalMachineEdges.cpp

@@ -0,0 +1,131 @@
+//===----------- BreakCriticalMachineEdges - Break critical edges ---------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by Fernando Pereira and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===---------------------------------------------------------------------===//
+//
+// Break all of the critical edges in the CFG by inserting a dummy basic block. 
+// This pass may be "required" by passes that cannot deal with critical edges.
+// Notice that this pass invalidates the CFG, because the same BasicBlock is 
+// used as parameter for the src MachineBasicBlock and the new dummy
+// MachineBasicBlock.
+//
+//===---------------------------------------------------------------------===//
+
+#include "llvm/CodeGen/Passes.h"
+#include "llvm/CodeGen/MachineFunctionPass.h"
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/CodeGen/MachineJumpTableInfo.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Support/Compiler.h"
+
+using namespace llvm;
+
+namespace {
+  struct VISIBILITY_HIDDEN BreakCriticalMachineEdges :
+                           public MachineFunctionPass {
+    static char ID; // Pass identification
+    BreakCriticalMachineEdges() : MachineFunctionPass((intptr_t)&ID) {}
+    
+    bool runOnMachineFunction(MachineFunction& Fn);
+    void splitCriticalEdge(MachineBasicBlock* A, MachineBasicBlock* B);
+  };
+  
+  char BreakCriticalMachineEdges::ID = 0;
+  RegisterPass<BreakCriticalMachineEdges> X("critical-machine-edges",
+                                            "Break critical machine code edges");
+}
+
+//const PassInfo *llvm::BreakCriticalMachineEdgesID = X.getPassInfo();
+
+void BreakCriticalMachineEdges::splitCriticalEdge(MachineBasicBlock* src,
+                                                  MachineBasicBlock* dst) {
+  const BasicBlock* srcBB = src->getBasicBlock();
+
+  MachineBasicBlock* crit_mbb = new MachineBasicBlock(srcBB);
+
+  // modify the llvm control flow graph
+  src->removeSuccessor(dst);
+  src->addSuccessor(crit_mbb);
+  crit_mbb->addSuccessor(dst);
+
+  // insert the new block into the machine function.
+  src->getParent()->getBasicBlockList().insert(src->getParent()->end(),
+                                               crit_mbb);
+
+  // insert a unconditional branch linking the new block to dst
+  const TargetMachine& TM = src->getParent()->getTarget();
+  const TargetInstrInfo* TII = TM.getInstrInfo();
+  std::vector<MachineOperand> emptyConditions;
+  TII->InsertBranch(*crit_mbb, dst, (MachineBasicBlock*)0, emptyConditions);
+
+  // modify every branch in src that points to dst to point to the new
+  // machine basic block instead:
+  MachineBasicBlock::iterator mii = src->end();
+  bool found_branch = false;
+  while (mii != src->begin()) {
+    mii--;
+    // if there are no more branches, finish the loop
+    if (!TII->isTerminatorInstr(mii->getOpcode())) {
+      break;
+    }
+    
+    // Scan the operands of this branch, replacing any uses of dst with
+    // crit_mbb.
+    for (unsigned i = 0, e = mii->getNumOperands(); i != e; ++i) {
+      MachineOperand & mo = mii->getOperand(i);
+      if (mo.isMachineBasicBlock() &&
+          mo.getMachineBasicBlock() == dst) {
+        found_branch = true;
+        mo.setMachineBasicBlock(crit_mbb);
+      }
+    }
+  }
+
+  // TODO: This is tentative. It may be necessary to fix this code. Maybe
+  // I am inserting too many gotos, but I am trusting that the asm printer
+  // will optimize the unnecessary gotos.
+  if(!found_branch) {
+    TII->InsertBranch(*src, crit_mbb, (MachineBasicBlock*)0, emptyConditions);
+  }
+
+  /// Change all the phi functions in dst, so that the incoming block be
+  /// crit_mbb, instead of src
+  for(mii = dst->begin(); mii != dst->end(); mii++) {
+    /// the first instructions are always phi functions.
+    if(mii->getOpcode() != TargetInstrInfo::PHI)
+      break;
+    
+    for (unsigned u = 0; u != mii->getNumOperands(); ++u)
+      if (mii->getOperand(u).isMachineBasicBlock() &&
+          mii->getOperand(u).getMachineBasicBlock() == src)
+        mii->getOperand(u).setMachineBasicBlock(crit_mbb);
+  }
+}
+
+bool BreakCriticalMachineEdges::runOnMachineFunction(MachineFunction& F) {
+  std::vector<MachineBasicBlock *> SourceBlocks;
+  std::vector<MachineBasicBlock *> DestBlocks;
+
+  for(MachineFunction::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
+    for(MachineBasicBlock::succ_iterator SI = FI->succ_begin(),
+        SE = FI->succ_end(); SI != SE; ++SI) {
+      // predecessor with multiple successors, successor with multiple
+      // predecessors.
+      if (FI->succ_size() > 1 && (*SI)->pred_size() > 1) {
+        SourceBlocks.push_back(FI);
+        DestBlocks.push_back(*SI);
+      }
+    }
+  }
+
+  for(unsigned u = 0; u < SourceBlocks.size() > 0; u++)
+    splitCriticalEdge(SourceBlocks[u], DestBlocks[u]);
+
+  return false;
+}