As Chris and Evan pointed out, BreakCriticalMachineEdges doesn't really need

to be a pass of its own.  Instead, move it out into a helper method.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@44002 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 94 insertions, 0 deletions

diff --git a/include/llvm/CodeGen/BreakCriticalMachineEdge.h b/include/llvm/CodeGen/BreakCriticalMachineEdge.h
new file mode 100644
index 0000000000..c02eaa784a
--- /dev/null
+++ b/include/llvm/CodeGen/BreakCriticalMachineEdge.h
@@ -0,0 +1,94 @@
+//===--------- BreakCriticalMachineEdges.h - 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.
+//
+//===---------------------------------------------------------------------===//
+//
+// Helper function to break a critical machine edge.
+//
+//===---------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_ASMPRINTER_H
+#define LLVM_CODEGEN_ASMPRINTER_H
+
+#include "llvm/CodeGen/MachineInstr.h"
+#include "llvm/CodeGen/MachineJumpTableInfo.h"
+#include "llvm/Target/TargetInstrInfo.h"
+#include "llvm/Target/TargetMachine.h"
+#include "llvm/Support/Compiler.h"
+
+namespace llvm {
+
+MachineBasicBlock* SplitCriticalMachineEdge(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);
+  }
+  
+  return crit_mbb;
+}
+
+}
+
+#endif