//
//===----------------------------------------------------------------------===//
-#include "llvm/Instructions.h"
#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
+#include "llvm/IR/Instructions.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
char MachineBranchProbabilityInfo::ID = 0;
-uint32_t MachineBranchProbabilityInfo::
-getSumForBlock(MachineBasicBlock *MBB) const {
- uint32_t Sum = 0;
+void MachineBranchProbabilityInfo::anchor() { }
+uint32_t MachineBranchProbabilityInfo::
+getSumForBlock(const MachineBasicBlock *MBB, uint32_t &Scale) const {
+ // First we compute the sum with 64-bits of precision, ensuring that cannot
+ // overflow by bounding the number of weights considered. Hopefully no one
+ // actually needs 2^32 successors.
+ assert(MBB->succ_size() < UINT32_MAX);
+ uint64_t Sum = 0;
+ Scale = 1;
for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
E = MBB->succ_end(); I != E; ++I) {
- MachineBasicBlock *Succ = *I;
- uint32_t Weight = getEdgeWeight(MBB, Succ);
- uint32_t PrevSum = Sum;
-
+ uint32_t Weight = getEdgeWeight(MBB, I);
Sum += Weight;
- assert(Sum > PrevSum); (void) PrevSum;
}
+ // If the computed sum fits in 32-bits, we're done.
+ if (Sum <= UINT32_MAX)
+ return Sum;
+
+ // Otherwise, compute the scale necessary to cause the weights to fit, and
+ // re-sum with that scale applied.
+ assert((Sum / UINT32_MAX) < UINT32_MAX);
+ Scale = (Sum / UINT32_MAX) + 1;
+ Sum = 0;
+ for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
+ E = MBB->succ_end(); I != E; ++I) {
+ uint32_t Weight = getEdgeWeight(MBB, I);
+ Sum += Weight / Scale;
+ }
+ assert(Sum <= UINT32_MAX);
return Sum;
}
-uint32_t
-MachineBranchProbabilityInfo::getEdgeWeight(MachineBasicBlock *Src,
- MachineBasicBlock *Dst) const {
+uint32_t MachineBranchProbabilityInfo::
+getEdgeWeight(const MachineBasicBlock *Src,
+ MachineBasicBlock::const_succ_iterator Dst) const {
uint32_t Weight = Src->getSuccWeight(Dst);
if (!Weight)
return DEFAULT_WEIGHT;
return Weight;
}
-bool MachineBranchProbabilityInfo::isEdgeHot(MachineBasicBlock *Src,
- MachineBasicBlock *Dst) const {
- // Hot probability is at least 4/5 = 80%
- uint32_t Weight = getEdgeWeight(Src, Dst);
- uint32_t Sum = getSumForBlock(Src);
+uint32_t MachineBranchProbabilityInfo::
+getEdgeWeight(const MachineBasicBlock *Src,
+ const MachineBasicBlock *Dst) const {
+ // This is a linear search. Try to use the const_succ_iterator version when
+ // possible.
+ return getEdgeWeight(Src, std::find(Src->succ_begin(), Src->succ_end(), Dst));
+}
- // FIXME: Implement BranchProbability::compare then change this code to
- // compare this BranchProbability against a static "hot" BranchProbability.
- return (uint64_t)Weight * 5 > (uint64_t)Sum * 4;
+bool
+MachineBranchProbabilityInfo::isEdgeHot(const MachineBasicBlock *Src,
+ const MachineBasicBlock *Dst) const {
+ // Hot probability is at least 4/5 = 80%
+ // FIXME: Compare against a static "hot" BranchProbability.
+ return getEdgeProbability(Src, Dst) > BranchProbability(4, 5);
}
MachineBasicBlock *
MachineBranchProbabilityInfo::getHotSucc(MachineBasicBlock *MBB) const {
- uint32_t Sum = 0;
uint32_t MaxWeight = 0;
- MachineBasicBlock *MaxSucc = 0;
-
+ MachineBasicBlock *MaxSucc = nullptr;
for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
E = MBB->succ_end(); I != E; ++I) {
- MachineBasicBlock *Succ = *I;
- uint32_t Weight = getEdgeWeight(MBB, Succ);
- uint32_t PrevSum = Sum;
-
- Sum += Weight;
- assert(Sum > PrevSum); (void) PrevSum;
-
+ uint32_t Weight = getEdgeWeight(MBB, I);
if (Weight > MaxWeight) {
MaxWeight = Weight;
- MaxSucc = Succ;
+ MaxSucc = *I;
}
}
- // FIXME: Use BranchProbability::compare.
- if ((uint64_t)MaxWeight * 5 >= (uint64_t)Sum * 4)
+ if (getEdgeProbability(MBB, MaxSucc) >= BranchProbability(4, 5))
return MaxSucc;
- return 0;
+ return nullptr;
}
-BranchProbability
-MachineBranchProbabilityInfo::getEdgeProbability(MachineBasicBlock *Src,
- MachineBasicBlock *Dst) const {
- uint32_t N = getEdgeWeight(Src, Dst);
- uint32_t D = getSumForBlock(Src);
+BranchProbability MachineBranchProbabilityInfo::getEdgeProbability(
+ const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const {
+ uint32_t Scale = 1;
+ uint32_t D = getSumForBlock(Src, Scale);
+ uint32_t N = getEdgeWeight(Src, Dst) / Scale;
return BranchProbability(N, D);
}
-raw_ostream &MachineBranchProbabilityInfo::
-printEdgeProbability(raw_ostream &OS, MachineBasicBlock *Src,
- MachineBasicBlock *Dst) const {
+raw_ostream &MachineBranchProbabilityInfo::printEdgeProbability(
+ raw_ostream &OS, const MachineBasicBlock *Src,
+ const MachineBasicBlock *Dst) const {
const BranchProbability Prob = getEdgeProbability(Src, Dst);
OS << "edge MBB#" << Src->getNumber() << " -> MBB#" << Dst->getNumber()
- << " probability is " << Prob
+ << " probability is " << Prob
<< (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n");
return OS;