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

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- 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
This commit is contained in:
Michael Liao 2014-09-24 04:59:06 +00:00
parent bfb2b180bf
commit 35fdc092e0
2 changed files with 13 additions and 9 deletions
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5
include/llvm/Transforms/Scalar.h
View File

@ -206,9 +206,10 @@ FunctionPass *createReassociatePass();
//===----------------------------------------------------------------------===// //===----------------------------------------------------------------------===//
// //
// JumpThreading - Thread control through mult-pred/multi-succ blocks where some // 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);
//===----------------------------------------------------------------------===// //===----------------------------------------------------------------------===//
// //

17
lib/Transforms/Scalar/JumpThreading.cpp
View File

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