Allow ARM if-converter to be run after post allocation scheduling.

- This fixed a number of bugs in if-converter, tail merging, and post-allocation
  scheduler. If-converter now runs branch folding / tail merging first to
  maximize if-conversion opportunities.
- Also changed the t2IT instruction slightly. It now defines the ITSTATE
  register which is read by instructions in the IT block.
- Added Thumb2 specific hazard recognizer to ensure the scheduler doesn't
  change the instruction ordering in the IT block (since IT mask has been
  finalized). It also ensures no other instructions can be scheduled between
  instructions in the IT block.

This is not yet enabled.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@106344 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 2 insertions, 16 deletions

diff --git a/lib/CodeGen/BranchFolding.cpp b/lib/CodeGen/BranchFolding.cpp
index e440e40f05..e17e47a662 100644
--- a/lib/CodeGen/BranchFolding.cpp
+++ b/lib/CodeGen/BranchFolding.cpp
@@ -358,24 +358,10 @@ static unsigned ComputeCommonTailLength(MachineBasicBlock *MBB1,
 }
 
 /// ReplaceTailWithBranchTo - Delete the instruction OldInst and everything
-/// after it, replacing it with an unconditional branch to NewDest.  This
-/// returns true if OldInst's block is modified, false if NewDest is modified.
+/// after it, replacing it with an unconditional branch to NewDest.
 void BranchFolder::ReplaceTailWithBranchTo(MachineBasicBlock::iterator OldInst,
                                            MachineBasicBlock *NewDest) {
-  MachineBasicBlock *OldBB = OldInst->getParent();
-
-  // Remove all the old successors of OldBB from the CFG.
-  while (!OldBB->succ_empty())
-    OldBB->removeSuccessor(OldBB->succ_begin());
-
-  // Remove all the dead instructions from the end of OldBB.
-  OldBB->erase(OldInst, OldBB->end());
-
-  // If OldBB isn't immediately before OldBB, insert a branch to it.
-  if (++MachineFunction::iterator(OldBB) != MachineFunction::iterator(NewDest))
-    TII->InsertBranch(*OldBB, NewDest, 0, SmallVector<MachineOperand, 0>(),
-                      OldInst->getDebugLoc());
-  OldBB->addSuccessor(NewDest);
+  TII->ReplaceTailWithBranchTo(OldInst, NewDest);
   ++NumTailMerge;
 }