1 files changed, 14 insertions, 13 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 2e0a07f105d..b7b644c981c 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -94,6 +94,12 @@ static cl::opt<unsigned> PHINodeFoldingThreshold(
     cl::desc(
         "Control the amount of phi node folding to perform (default = 2)"));
 
+static cl::opt<unsigned> TwoEntryPHINodeFoldingThreshold(
+    "two-entry-phi-node-folding-threshold", cl::Hidden, cl::init(4),
+    cl::desc("Control the maximal total instruction cost that we are willing "
+             "to speculatively execute to fold a 2-entry PHI node into a "
+             "select (default = 4)"));
+
 static cl::opt<bool> DupRet(
     "simplifycfg-dup-ret", cl::Hidden, cl::init(false),
     cl::desc("Duplicate return instructions into unconditional branches"));
@@ -332,7 +338,7 @@ static unsigned ComputeSpeculationCost(const User *I,
 /// CostRemaining, false is returned and CostRemaining is undefined.
 static bool DominatesMergePoint(Value *V, BasicBlock *BB,
                                 SmallPtrSetImpl<Instruction *> &AggressiveInsts,
-                                unsigned &CostRemaining,
+                                int &BudgetRemaining,
                                 const TargetTransformInfo &TTI,
                                 unsigned Depth = 0) {
   // It is possible to hit a zero-cost cycle (phi/gep instructions for example),
@@ -375,7 +381,7 @@ static bool DominatesMergePoint(Value *V, BasicBlock *BB,
   if (!isSafeToSpeculativelyExecute(I))
     return false;
 
-  unsigned Cost = ComputeSpeculationCost(I, TTI);
+  BudgetRemaining -= ComputeSpeculationCost(I, TTI);
 
   // Allow exactly one instruction to be speculated regardless of its cost
   // (as long as it is safe to do so).
@@ -383,17 +389,14 @@ static bool DominatesMergePoint(Value *V, BasicBlock *BB,
   // or other expensive operation. The speculation of an expensive instruction
   // is expected to be undone in CodeGenPrepare if the speculation has not
   // enabled further IR optimizations.
-  if (Cost > CostRemaining &&
+  if (BudgetRemaining < 0 &&
       (!SpeculateOneExpensiveInst || !AggressiveInsts.empty() || Depth > 0))
     return false;
 
-  // Avoid unsigned wrap.
-  CostRemaining = (Cost > CostRemaining) ? 0 : CostRemaining - Cost;
-
   // Okay, we can only really hoist these out if their operands do
   // not take us over the cost threshold.
   for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
-    if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining, TTI,
+    if (!DominatesMergePoint(*i, BB, AggressiveInsts, BudgetRemaining, TTI,
                              Depth + 1))
       return false;
   // Okay, it's safe to do this!  Remember this instruction.
@@ -2322,10 +2325,8 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
   // instructions.  While we are at it, keep track of the instructions
   // that need to be moved to the dominating block.
   SmallPtrSet<Instruction *, 4> AggressiveInsts;
-  unsigned MaxCostVal0 = PHINodeFoldingThreshold,
-           MaxCostVal1 = PHINodeFoldingThreshold;
-  MaxCostVal0 *= TargetTransformInfo::TCC_Basic;
-  MaxCostVal1 *= TargetTransformInfo::TCC_Basic;
+  int BudgetRemaining =
+      TwoEntryPHINodeFoldingThreshold * TargetTransformInfo::TCC_Basic;
 
   for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
     PHINode *PN = cast<PHINode>(II++);
@@ -2336,9 +2337,9 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
     }
 
     if (!DominatesMergePoint(PN->getIncomingValue(0), BB, AggressiveInsts,
-                             MaxCostVal0, TTI) ||
+                             BudgetRemaining, TTI) ||
         !DominatesMergePoint(PN->getIncomingValue(1), BB, AggressiveInsts,
-                             MaxCostVal1, TTI))
+                             BudgetRemaining, TTI))
       return false;
   }