//
//===----------------------------------------------------------------------===//
-#include "llvm/Constants.h"
-#include "llvm/Function.h"
-#include "llvm/Instructions.h"
-#include "llvm/LLVMContext.h"
-#include "llvm/Metadata.h"
+#define DEBUG_TYPE "branch-prob"
#include "llvm/Analysis/BranchProbabilityInfo.h"
-#include "llvm/Analysis/LoopInfo.h"
#include "llvm/ADT/PostOrderIterator.h"
-#include "llvm/Support/CFG.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/IR/CFG.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Metadata.h"
#include "llvm/Support/Debug.h"
using namespace llvm;
/// easily subsume it.
static const uint32_t UR_NONTAKEN_WEIGHT = 1024*1024 - 1;
+/// \brief Weight for a branch taken going into a cold block.
+///
+/// This is the weight for a branch taken toward a block marked
+/// cold. A block is marked cold if it's postdominated by a
+/// block containing a call to a cold function. Cold functions
+/// are those marked with attribute 'cold'.
+static const uint32_t CC_TAKEN_WEIGHT = 4;
+
+/// \brief Weight for a branch not-taken into a cold block.
+///
+/// This is the weight for a branch not taken toward a block marked
+/// cold.
+static const uint32_t CC_NONTAKEN_WEIGHT = 64;
+
static const uint32_t PH_TAKEN_WEIGHT = 20;
static const uint32_t PH_NONTAKEN_WEIGHT = 12;
uint32_t UnreachableWeight =
std::max(UR_TAKEN_WEIGHT / (unsigned)UnreachableEdges.size(), MIN_WEIGHT);
- for (SmallVector<unsigned, 4>::iterator I = UnreachableEdges.begin(),
- E = UnreachableEdges.end();
+ for (SmallVectorImpl<unsigned>::iterator I = UnreachableEdges.begin(),
+ E = UnreachableEdges.end();
I != E; ++I)
setEdgeWeight(BB, *I, UnreachableWeight);
uint32_t ReachableWeight =
std::max(UR_NONTAKEN_WEIGHT / (unsigned)ReachableEdges.size(),
NORMAL_WEIGHT);
- for (SmallVector<unsigned, 4>::iterator I = ReachableEdges.begin(),
- E = ReachableEdges.end();
+ for (SmallVectorImpl<unsigned>::iterator I = ReachableEdges.begin(),
+ E = ReachableEdges.end();
I != E; ++I)
setEdgeWeight(BB, *I, ReachableWeight);
return true;
}
+/// \brief Calculate edge weights for edges leading to cold blocks.
+///
+/// A cold block is one post-dominated by a block with a call to a
+/// cold function. Those edges are unlikely to be taken, so we give
+/// them relatively low weight.
+///
+/// Return true if we could compute the weights for cold edges.
+/// Return false, otherwise.
+bool BranchProbabilityInfo::calcColdCallHeuristics(BasicBlock *BB) {
+ TerminatorInst *TI = BB->getTerminator();
+ if (TI->getNumSuccessors() == 0)
+ return false;
+
+ // Determine which successors are post-dominated by a cold block.
+ SmallVector<unsigned, 4> ColdEdges;
+ SmallVector<unsigned, 4> NormalEdges;
+ for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I)
+ if (PostDominatedByColdCall.count(*I))
+ ColdEdges.push_back(I.getSuccessorIndex());
+ else
+ NormalEdges.push_back(I.getSuccessorIndex());
+
+ // If all successors are in the set of blocks post-dominated by cold calls,
+ // this block is in the set post-dominated by cold calls.
+ if (ColdEdges.size() == TI->getNumSuccessors())
+ PostDominatedByColdCall.insert(BB);
+ else {
+ // Otherwise, if the block itself contains a cold function, add it to the
+ // set of blocks postdominated by a cold call.
+ assert(!PostDominatedByColdCall.count(BB));
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
+ if (CallInst *CI = dyn_cast<CallInst>(I))
+ if (CI->hasFnAttr(Attribute::Cold)) {
+ PostDominatedByColdCall.insert(BB);
+ break;
+ }
+ }
+
+ // Skip probabilities if this block has a single successor.
+ if (TI->getNumSuccessors() == 1 || ColdEdges.empty())
+ return false;
+
+ uint32_t ColdWeight =
+ std::max(CC_TAKEN_WEIGHT / (unsigned) ColdEdges.size(), MIN_WEIGHT);
+ for (SmallVectorImpl<unsigned>::iterator I = ColdEdges.begin(),
+ E = ColdEdges.end();
+ I != E; ++I)
+ setEdgeWeight(BB, *I, ColdWeight);
+
+ if (NormalEdges.empty())
+ return true;
+ uint32_t NormalWeight = std::max(
+ CC_NONTAKEN_WEIGHT / (unsigned) NormalEdges.size(), NORMAL_WEIGHT);
+ for (SmallVectorImpl<unsigned>::iterator I = NormalEdges.begin(),
+ E = NormalEdges.end();
+ I != E; ++I)
+ setEdgeWeight(BB, *I, NormalWeight);
+
+ return true;
+}
+
// Calculate Edge Weights using "Pointer Heuristics". Predict a comparsion
// between two pointer or pointer and NULL will fail.
bool BranchProbabilityInfo::calcPointerHeuristics(BasicBlock *BB) {
if (backWeight < NORMAL_WEIGHT)
backWeight = NORMAL_WEIGHT;
- for (SmallVector<unsigned, 8>::iterator EI = BackEdges.begin(),
+ for (SmallVectorImpl<unsigned>::iterator EI = BackEdges.begin(),
EE = BackEdges.end(); EI != EE; ++EI) {
setEdgeWeight(BB, *EI, backWeight);
}
if (inWeight < NORMAL_WEIGHT)
inWeight = NORMAL_WEIGHT;
- for (SmallVector<unsigned, 8>::iterator EI = InEdges.begin(),
+ for (SmallVectorImpl<unsigned>::iterator EI = InEdges.begin(),
EE = InEdges.end(); EI != EE; ++EI) {
setEdgeWeight(BB, *EI, inWeight);
}
if (exitWeight < MIN_WEIGHT)
exitWeight = MIN_WEIGHT;
- for (SmallVector<unsigned, 8>::iterator EI = ExitingEdges.begin(),
+ for (SmallVectorImpl<unsigned>::iterator EI = ExitingEdges.begin(),
EE = ExitingEdges.end(); EI != EE; ++EI) {
setEdgeWeight(BB, *EI, exitWeight);
}
// InstCombine canonicalizes X <= 0 into X < 1.
// X <= 0 -> Unlikely
isProb = false;
- } else if (CV->isAllOnesValue() && CI->getPredicate() == CmpInst::ICMP_SGT) {
- // InstCombine canonicalizes X >= 0 into X > -1.
- // X >= 0 -> Likely
- isProb = true;
+ } else if (CV->isAllOnesValue()) {
+ switch (CI->getPredicate()) {
+ case CmpInst::ICMP_EQ:
+ // X == -1 -> Unlikely
+ isProb = false;
+ break;
+ case CmpInst::ICMP_NE:
+ // X != -1 -> Likely
+ isProb = true;
+ break;
+ case CmpInst::ICMP_SGT:
+ // InstCombine canonicalizes X >= 0 into X > -1.
+ // X >= 0 -> Likely
+ isProb = true;
+ break;
+ default:
+ return false;
+ }
} else {
return false;
}
}
bool BranchProbabilityInfo::runOnFunction(Function &F) {
+ DEBUG(dbgs() << "---- Branch Probability Info : " << F.getName()
+ << " ----\n\n");
LastF = &F; // Store the last function we ran on for printing.
LI = &getAnalysis<LoopInfo>();
assert(PostDominatedByUnreachable.empty());
+ assert(PostDominatedByColdCall.empty());
// Walk the basic blocks in post-order so that we can build up state about
// the successors of a block iteratively.
continue;
if (calcMetadataWeights(*I))
continue;
+ if (calcColdCallHeuristics(*I))
+ continue;
if (calcLoopBranchHeuristics(*I))
continue;
if (calcPointerHeuristics(*I))
}
PostDominatedByUnreachable.clear();
+ PostDominatedByColdCall.clear();
return false;
}
return DEFAULT_WEIGHT;
}
+uint32_t
+BranchProbabilityInfo::
+getEdgeWeight(const BasicBlock *Src, succ_const_iterator Dst) const {
+ size_t index = std::distance(succ_begin(Src), Dst);
+ return getEdgeWeight(Src, index);
+}
+
/// Get the raw edge weight calculated for the block pair. This returns the sum
/// of all raw edge weights from Src to Dst.
uint32_t BranchProbabilityInfo::
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