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Record whether the weights on out-edges from a MBB are normalized.

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1. Create a utility function normalizeEdgeWeights() in MachineBranchProbabilityInfo that normalizes a list of edge weights so that the sum of then can fit in uint32_t.
2. Provide an interface in MachineBasicBlock to normalize its successors' weights.
3. Add a flag in MachineBasicBlock that tracks whether its successors' weights are normalized.
4. Provide an overload of getSumForBlock that accepts a non-const pointer to a MBB so that it can force normalizing this MBB's successors' weights.
5. Update several uses of getSumForBlock() by eliminating the once needed weight scale.

Differential Revision: http://reviews.llvm.org/D11442

llvm-svn: 244154
This commit is contained in:
Cong Hou
2015-08-05 22:01:20 +00:00
parent 758f3f542a
commit 36e7e52aa4
6 changed files with 106 additions and 42 deletions
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30
llvm/lib/CodeGen/MachineBasicBlock.cpp
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@@ -16,6 +16,7 @@
#include "llvm/ADT/SmallString.h"
#include "llvm/CodeGen/LiveIntervalAnalysis.h"
#include "llvm/CodeGen/LiveVariables.h"
#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
@@ -39,8 +40,9 @@ using namespace llvm;
#define DEBUG_TYPE "codegen"
MachineBasicBlock::MachineBasicBlock(MachineFunction &mf, const BasicBlock *bb)
: BB(bb), Number(-1), xParent(&mf), Alignment(0), IsLandingPad(false),
AddressTaken(false), CachedMCSymbol(nullptr) {
: BB(bb), Number(-1), AreSuccWeightsNormalized(false), xParent(&mf),
Alignment(0), IsLandingPad(false), AddressTaken(false),
CachedMCSymbol(nullptr) {
Insts.Parent = this;
}
@@ -481,8 +483,10 @@ void MachineBasicBlock::addSuccessor(MachineBasicBlock *succ, uint32_t weight) {
if (weight != 0 && Weights.empty())
Weights.resize(Successors.size());
if (weight != 0 || !Weights.empty())
if (weight != 0 || !Weights.empty()) {
Weights.push_back(weight);
AreSuccWeightsNormalized = false;
}
Successors.push_back(succ);
succ->addPredecessor(this);
@@ -1096,7 +1100,25 @@ uint32_t MachineBasicBlock::getSuccWeight(const_succ_iterator Succ) const {
void MachineBasicBlock::setSuccWeight(succ_iterator I, uint32_t weight) {
if (Weights.empty())
return;
*getWeightIterator(I) = weight;
auto WeightIter = getWeightIterator(I);
uint32_t OldWeight = *WeightIter;
*WeightIter = weight;
if (weight > OldWeight)
AreSuccWeightsNormalized = false;
}
/// Normalize all succesor weights so that the sum of them does not exceed
/// UINT32_MAX. Return true if the weights are modified and false otherwise.
/// Note that weights that are modified after calling this function are not
/// guaranteed to be normalized.
bool MachineBasicBlock::normalizeSuccWeights() {
if (!AreSuccWeightsNormalized) {
uint32_t Scale =
MachineBranchProbabilityInfo::normalizeEdgeWeights(Weights);
AreSuccWeightsNormalized = true;
return Scale != 1;
}
return false;
}
/// getWeightIterator - Return wight iterator corresonding to the I successor