Allow BB duplication threshold to be adjusted through JumpThreading's ctor

- BB duplication may not be desired on targets where there is no or small
  branch penalty and code duplication needs restrict control.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218375 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/Transforms/Scalar.h b/include/llvm/Transforms/Scalar.h
index 7a561ee5b24afd31879208a8f4d693d318dcbee4..52170fac29cc700cf9950647f94fd2b0a836da22 100644 (file)
--- a/include/llvm/Transforms/Scalar.h
+++ b/include/llvm/Transforms/Scalar.h
@@ -206,9 +206,10 @@ FunctionPass *createReassociatePass();
 //===----------------------------------------------------------------------===//
 //
 // JumpThreading - Thread control through mult-pred/multi-succ blocks where some
-// preds always go to some succ.
+// preds always go to some succ. Thresholds other than minus one override the
+// internal BB duplication default threshold.
 //
-FunctionPass *createJumpThreadingPass();
+FunctionPass *createJumpThreadingPass(int Threshold = -1);
 
 //===----------------------------------------------------------------------===//
 //

diff --git a/lib/Transforms/Scalar/JumpThreading.cpp b/lib/Transforms/Scalar/JumpThreading.cpp
index bd8c0e8e6995cf720401487e10c9edd43a27dc59..924d4e146776109b6127a5275289431dada49adb 100644 (file)
--- a/lib/Transforms/Scalar/JumpThreading.cpp
+++ b/lib/Transforms/Scalar/JumpThreading.cpp
@@ -45,7 +45,7 @@ STATISTIC(NumFolds,   "Number of terminators folded");
 STATISTIC(NumDupes,   "Number of branch blocks duplicated to eliminate phi");
 
 static cl::opt<unsigned>
-Threshold("jump-threading-threshold",
+BBDuplicateThreshold("jump-threading-threshold",
           cl::desc("Max block size to duplicate for jump threading"),
           cl::init(6), cl::Hidden);
 
@@ -88,6 +88,8 @@ namespace {
 #endif
     DenseSet<std::pair<Value*, BasicBlock*> > RecursionSet;
 
+    unsigned BBDupThreshold;
+
     // RAII helper for updating the recursion stack.
     struct RecursionSetRemover {
       DenseSet<std::pair<Value*, BasicBlock*> > &TheSet;
@@ -103,7 +105,8 @@ namespace {
     };
   public:
     static char ID; // Pass identification
-    JumpThreading() : FunctionPass(ID) {
+    JumpThreading(int T = -1) : FunctionPass(ID) {
+      BBDupThreshold = (T == -1) ? BBDuplicateThreshold : unsigned(T);
       initializeJumpThreadingPass(*PassRegistry::getPassRegistry());
     }
 
@@ -147,7 +150,7 @@ INITIALIZE_PASS_END(JumpThreading, "jump-threading",
                 "Jump Threading", false, false)
 
 // Public interface to the Jump Threading pass
-FunctionPass *llvm::createJumpThreadingPass() { return new JumpThreading(); }
+FunctionPass *llvm::createJumpThreadingPass(int Threshold) { return new JumpThreading(Threshold); }
 
 /// runOnFunction - Top level algorithm.
 ///
@@ -1389,8 +1392,8 @@ bool JumpThreading::ThreadEdge(BasicBlock *BB,
     return false;
   }
 
-  unsigned JumpThreadCost = getJumpThreadDuplicationCost(BB, Threshold);
-  if (JumpThreadCost > Threshold) {
+  unsigned JumpThreadCost = getJumpThreadDuplicationCost(BB, BBDupThreshold);
+  if (JumpThreadCost > BBDupThreshold) {
     DEBUG(dbgs() << "  Not threading BB '" << BB->getName()
           << "' - Cost is too high: " << JumpThreadCost << "\n");
     return false;
@@ -1532,8 +1535,8 @@ bool JumpThreading::DuplicateCondBranchOnPHIIntoPred(BasicBlock *BB,
     return false;
   }
 
-  unsigned DuplicationCost = getJumpThreadDuplicationCost(BB, Threshold);
-  if (DuplicationCost > Threshold) {
+  unsigned DuplicationCost = getJumpThreadDuplicationCost(BB, BBDupThreshold);
+  if (DuplicationCost > BBDupThreshold) {
     DEBUG(dbgs() << "  Not duplicating BB '" << BB->getName()
           << "' - Cost is too high: " << DuplicationCost << "\n");
     return false;