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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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2
include/llvm/CodeGen/MachineBasicBlock.h
View File

@ -574,7 +574,7 @@ 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

@ -942,12 +942,11 @@ 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;