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Fix a quadratic algorithm in MachineBranchProbabilityInfo.

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The getSumForBlock function was quadratic in the number of successors
because getSuccWeight would perform a linear search for an already known
iterator.

This patch was originally committed as r161460, but reverted again
because of assertion failures. Now that duplicate Machine CFG edges have
been eliminated, this works properly.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@162233 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Jakob Stoklund Olesen
2012-08-20 22:01:38 +00:00
parent e7fdef420d
commit 990ca5517f
4 changed files with 23 additions and 13 deletions
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lib/CodeGen/MachineBranchProbabilityInfo.cpp
+14 -6
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@@ -38,7 +38,7 @@ getSumForBlock(const MachineBasicBlock *MBB, uint32_t &Scale) const {
Scale = 1;
for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
E = MBB->succ_end(); I != E; ++I) {
uint32_t Weight = getEdgeWeight(MBB, *I);
uint32_t Weight = getEdgeWeight(MBB, I);
Sum += Weight;
}
@@ -53,22 +53,30 @@ getSumForBlock(const MachineBasicBlock *MBB, uint32_t &Scale) const {
Sum = 0;
for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
E = MBB->succ_end(); I != E; ++I) {
uint32_t Weight = getEdgeWeight(MBB, *I);
uint32_t Weight = getEdgeWeight(MBB, I);
Sum += Weight / Scale;
}
assert(Sum <= UINT32_MAX);
return Sum;
}
uint32_t
MachineBranchProbabilityInfo::getEdgeWeight(const MachineBasicBlock *Src,
const 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;
}
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));
}
bool MachineBranchProbabilityInfo::isEdgeHot(MachineBasicBlock *Src,
MachineBasicBlock *Dst) const {
// Hot probability is at least 4/5 = 80%
@@ -82,7 +90,7 @@ MachineBranchProbabilityInfo::getHotSucc(MachineBasicBlock *MBB) const {
MachineBasicBlock *MaxSucc = 0;
for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
E = MBB->succ_end(); I != E; ++I) {
uint32_t Weight = getEdgeWeight(MBB, *I);
uint32_t Weight = getEdgeWeight(MBB, I);
if (Weight > MaxWeight) {
MaxWeight = Weight;
MaxSucc = *I;