Codegen: Factor out canTailDuplicate

canTailDuplicate accepts two blocks and returns true if the first can be
duplicated into the second successfully. Use this function to
encapsulate the heuristic.

llvm-svn: 276062

1 files changed, 19 insertions, 9 deletions

diff --git a/llvm/lib/CodeGen/TailDuplicator.cpp b/llvm/lib/CodeGen/TailDuplicator.cpp
index 847a09349a5..f2349f28243 100644
--- a/llvm/lib/CodeGen/TailDuplicator.cpp
+++ b/llvm/lib/CodeGen/TailDuplicator.cpp
@@ -717,6 +717,21 @@ bool TailDuplicator::duplicateSimpleBB(
   return Changed;
 }
 
+bool TailDuplicator::canTailDuplicate(MachineBasicBlock *TailBB,
+                                      MachineBasicBlock *PredBB) {
+  // EH edges are ignored by AnalyzeBranch.
+  if (PredBB->succ_size() > 1)
+    return false;
+
+  MachineBasicBlock *PredTBB, *PredFBB;
+  SmallVector<MachineOperand, 4> PredCond;
+  if (TII->analyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true))
+    return false;
+  if (!PredCond.empty())
+    return false;
+  return true;
+}
+
 /// If it is profitable, duplicate TailBB's contents in each
 /// of its predecessors.
 bool TailDuplicator::tailDuplicate(MachineFunction &MF, bool IsSimple,
@@ -741,19 +756,12 @@ bool TailDuplicator::tailDuplicate(MachineFunction &MF, bool IsSimple,
                                                         PE = Preds.end();
        PI != PE; ++PI) {
     MachineBasicBlock *PredBB = *PI;
-
     assert(TailBB != PredBB &&
            "Single-block loop should have been rejected earlier!");
-    // EH edges are ignored by AnalyzeBranch.
-    if (PredBB->succ_size() > 1)
-      continue;
 
-    MachineBasicBlock *PredTBB, *PredFBB;
-    SmallVector<MachineOperand, 4> PredCond;
-    if (TII->analyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true))
-      continue;
-    if (!PredCond.empty())
+    if (!canTailDuplicate(TailBB, PredBB))
       continue;
+
     // Don't duplicate into a fall-through predecessor (at least for now).
     if (PredBB->isLayoutSuccessor(TailBB) && PredBB->canFallThrough())
       continue;
@@ -788,6 +796,8 @@ bool TailDuplicator::tailDuplicate(MachineFunction &MF, bool IsSimple,
     appendCopies(PredBB, CopyInfos, Copies);
 
     // Simplify
+    MachineBasicBlock *PredTBB, *PredFBB;
+    SmallVector<MachineOperand, 4> PredCond;
     TII->analyzeBranch(*PredBB, PredTBB, PredFBB, PredCond, true);
 
     NumTailDupAdded += TailBB->size() - 1; // subtract one for removed branch