4 files changed, 18 insertions, 17 deletions

diff --git a/llvm/include/llvm/Target/TargetInstrInfo.h b/llvm/include/llvm/Target/TargetInstrInfo.h
index 72ebe3cafac..8070d458588 100644
--- a/llvm/include/llvm/Target/TargetInstrInfo.h
+++ b/llvm/include/llvm/Target/TargetInstrInfo.h
@@ -544,12 +544,9 @@ public:
   virtual unsigned getInlineAsmLength(const char *Str,
                                       const MCAsmInfo &MAI) const;
 
-  /// TailDuplicationLimit - Returns the limit on the number of instructions
-  /// in basic block MBB beyond which it will not be tail-duplicated.
-  virtual unsigned TailDuplicationLimit(const MachineBasicBlock &MBB,
-                                        unsigned DefaultLimit) const {
-    return DefaultLimit;
-  }
+  /// isProfitableToDuplicateIndirectBranch - Returns true if tail duplication
+  /// is especially profitable for indirect branches.
+  virtual bool isProfitableToDuplicateIndirectBranch() const { return false; }
 };
 
 /// TargetInstrInfoImpl - This is the default implementation of
diff --git a/llvm/lib/CodeGen/BranchFolding.cpp b/llvm/lib/CodeGen/BranchFolding.cpp
index f807e8fa261..0fd3c23085d 100644
--- a/llvm/lib/CodeGen/BranchFolding.cpp
+++ b/llvm/lib/CodeGen/BranchFolding.cpp
@@ -1043,9 +1043,18 @@ bool BranchFolder::TailDuplicate(MachineBasicBlock *TailBB,
   // of one less than the tail-merge threshold. When optimizing for size,
   // duplicate only one, because one branch instruction can be eliminated to
   // compensate for the duplication.
-  unsigned MaxDuplicateCount =
-    MF.getFunction()->hasFnAttr(Attribute::OptimizeForSize) ?
-    1 : TII->TailDuplicationLimit(*TailBB, TailMergeSize - 1);
+  unsigned MaxDuplicateCount;
+  if (MF.getFunction()->hasFnAttr(Attribute::OptimizeForSize))
+    MaxDuplicateCount = 1;
+  else if (TII->isProfitableToDuplicateIndirectBranch() &&
+           !TailBB->empty() && TailBB->back().getDesc().isIndirectBranch())
+    // If the target has hardware branch prediction that can handle indirect
+    // branches, duplicating them can often make them predictable when there
+    // are common paths through the code.  The limit needs to be high enough
+    // to allow undoing the effects of tail merging.
+    MaxDuplicateCount = 20;
+  else
+    MaxDuplicateCount = TailMergeSize - 1;
 
   // Check the instructions in the block to determine whether tail-duplication
   // is invalid or unlikely to be profitable.
diff --git a/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp b/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
index c92ec368a79..705f97097c1 100644
--- a/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
+++ b/llvm/lib/Target/ARM/ARMBaseInstrInfo.cpp
@@ -1027,14 +1027,10 @@ bool ARMBaseInstrInfo::isIdentical(const MachineInstr *MI0,
   return TargetInstrInfoImpl::isIdentical(MI0, MI1, MRI);
 }
 
-unsigned ARMBaseInstrInfo::TailDuplicationLimit(const MachineBasicBlock &MBB,
-                                                unsigned DefaultLimit) const {
+bool ARMBaseInstrInfo::isProfitableToDuplicateIndirectBranch() const {
   // If the target processor can predict indirect branches, it is highly
   // desirable to duplicate them, since it can often make them predictable.
-  if (!MBB.empty() && isIndirectBranchOpcode(MBB.back().getOpcode()) &&
-      getSubtarget().hasBranchTargetBuffer())
-    return DefaultLimit + 2;
-  return DefaultLimit;
+  return getSubtarget().hasBranchTargetBuffer();
 }
 
 /// getInstrPredicate - If instruction is predicated, returns its predicate
diff --git a/llvm/lib/Target/ARM/ARMBaseInstrInfo.h b/llvm/lib/Target/ARM/ARMBaseInstrInfo.h
index dbd4f63619d..7944f354b9b 100644
--- a/llvm/lib/Target/ARM/ARMBaseInstrInfo.h
+++ b/llvm/lib/Target/ARM/ARMBaseInstrInfo.h
@@ -291,8 +291,7 @@ public:
   virtual bool isIdentical(const MachineInstr *MI, const MachineInstr *Other,
                            const MachineRegisterInfo *MRI) const;
 
-  virtual unsigned TailDuplicationLimit(const MachineBasicBlock &MBB,
-                                        unsigned DefaultLimit) const;
+  virtual bool isProfitableToDuplicateIndirectBranch() const;
 };
 
 static inline