Import LLVM, at r72732.

1 files changed, 108 insertions, 0 deletions

diff --git a/include/llvm/CodeGen/BreakCriticalMachineEdge.h b/include/llvm/CodeGen/BreakCriticalMachineEdge.h
new file mode 100644
index 0000000..4861297
--- /dev/null
+++ b/include/llvm/CodeGen/BreakCriticalMachineEdge.h
@@ -0,0 +1,108 @@
+//===--------- BreakCriticalMachineEdge.h - Break critical edges ---------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===---------------------------------------------------------------------===//
+//
+// Helper function to break a critical machine edge.
+//
+//===---------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_BREAKCRITICALMACHINEEDGE_H
+#define LLVM_CODEGEN_BREAKCRITICALMACHINEEDGE_H
+
+#include "llvm/CodeGen/MachineJumpTableInfo.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Target/TargetMachine.h"
+
+namespace llvm {
+
+MachineBasicBlock* SplitCriticalMachineEdge(MachineBasicBlock* src,
+                                            MachineBasicBlock* dst) {
+  MachineFunction &MF = *src->getParent();
+  const BasicBlock* srcBB = src->getBasicBlock();
+
+  MachineBasicBlock* crit_mbb = MF.CreateMachineBasicBlock(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.
+  MF.push_back(crit_mbb);
+
+  // insert a unconditional branch linking the new block to dst
+  const TargetMachine& TM = MF.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 (!mii->getDesc().isTerminator()) {
+      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.isMBB() && mo.getMBB() == dst) {
+        found_branch = true;
+        mo.setMBB(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;
+
+    // Find the operands corresponding to the source block
+    std::vector<unsigned> toRemove;
+    unsigned reg = 0;
+    for (unsigned u = 0; u != mii->getNumOperands(); ++u)
+      if (mii->getOperand(u).isMBB() &&
+          mii->getOperand(u).getMBB() == src) {
+        reg = mii->getOperand(u-1).getReg();
+        toRemove.push_back(u-1);
+      }
+    // Remove all uses of this MBB
+    for (std::vector<unsigned>::reverse_iterator I = toRemove.rbegin(),
+         E = toRemove.rend(); I != E; ++I) {
+      mii->RemoveOperand(*I+1);
+      mii->RemoveOperand(*I);
+    }
+
+    // Add a single use corresponding to the new MBB
+    mii->addOperand(MachineOperand::CreateReg(reg, false));
+    mii->addOperand(MachineOperand::CreateMBB(crit_mbb));
+  }
+
+  return crit_mbb;
+}
+
+}
+
+#endif