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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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@161460 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Jakob Stoklund Olesen 2012-08-08 00:20:37 +00:00
parent 9d1747c3cd
commit 5e63d43e48
4 changed files with 23 additions and 13 deletions
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2
include/llvm/CodeGen/MachineBasicBlock.h
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@ -572,7 +572,7 @@ private:
/// getSuccWeight - Return weight of the edge from this block to MBB. This
/// method should NOT be called directly, but by using getEdgeWeight method
/// from MachineBranchProbabilityInfo class.
uint32_t getSuccWeight(const MachineBasicBlock *succ) const;
uint32_t getSuccWeight(const_succ_iterator Succ) const;
// Methods used to maintain doubly linked list of blocks...

9
include/llvm/CodeGen/MachineBranchProbabilityInfo.h
View File

@ -16,14 +16,12 @@
#define LLVM_CODEGEN_MACHINEBRANCHPROBABILITYINFO_H
#include "llvm/Pass.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/Support/BranchProbability.h"
#include <climits>
namespace llvm {
class raw_ostream;
class MachineBasicBlock;
class MachineBranchProbabilityInfo : public ImmutablePass {
virtual void anchor();
@ -52,6 +50,11 @@ public:
uint32_t getEdgeWeight(const MachineBasicBlock *Src,
const MachineBasicBlock *Dst) const;
// Same thing, but using a const_succ_iterator from Src. This is faster when
// the iterator is already available.
uint32_t getEdgeWeight(const MachineBasicBlock *Src,
MachineBasicBlock::const_succ_iterator Dst) const;
// Get sum of the block successors' weights, potentially scaling them to fit
// within 32-bits. If scaling is required, sets Scale based on the necessary
// adjustment. Any edge weights used with the sum should be divided by Scale.

5
lib/CodeGen/MachineBasicBlock.cpp
View File

@ -912,12 +912,11 @@ MachineBasicBlock::findDebugLoc(instr_iterator MBBI) {
/// getSuccWeight - Return weight of the edge from this block to MBB.
///
uint32_t MachineBasicBlock::getSuccWeight(const MachineBasicBlock *succ) const {
uint32_t MachineBasicBlock::getSuccWeight(const_succ_iterator Succ) const {
if (Weights.empty())
return 0;
const_succ_iterator I = std::find(Successors.begin(), Successors.end(), succ);
return *getWeightIterator(I);
return *getWeightIterator(Succ);
}
/// getWeightIterator - Return wight iterator corresonding to the I successor

20
lib/CodeGen/MachineBranchProbabilityInfo.cpp
View File

@ -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;