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Add two thresholds lvi-overdefined-BB-threshold and lvi-overdefined-threshold 

for LVI algorithm. For a specific value to be lowered, when the number of basic
blocks being checked for overdefined lattice value is larger than
lvi-overdefined-BB-threshold, or the times of encountering overdefined value
for a single basic block is larger than lvi-overdefined-threshold, the LVI
algorithm will stop further lowering the lattice value.

llvm-svn: 218231
This commit is contained in:
Jiangning Liu 2014-09-22 02:23:05 +00:00
parent 31097581aa
commit cd1d79e77c
1 changed files with 31 additions and 1 deletions
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32
llvm/lib/Analysis/LazyValueInfo.cpp
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@ -27,6 +27,7 @@
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetLibraryInfo.h"
@ -37,6 +38,20 @@ using namespace PatternMatch;
#define DEBUG_TYPE "lazy-value-info"
// Experimentally derived threshold for the number of basic blocks lowered for
// lattice value overdefined.
static cl::opt<unsigned>
OverdefinedBBThreshold("lvi-overdefined-BB-threshold",
cl::init(1500), cl::Hidden,
cl::desc("Threshold of the number of basic blocks lowered for lattice value"
"'overdefined'."));
// Experimentally derived threshold for additional lowering lattice values
// overdefined per block.
static cl::opt<unsigned>
OverdefinedThreshold("lvi-overdefined-threshold", cl::init(10), cl::Hidden,
cl::desc("Threshold of lowering lattice value 'overdefined'."));
char LazyValueInfo::ID = 0;
INITIALIZE_PASS_BEGIN(LazyValueInfo, "lazy-value-info",
"Lazy Value Information Analysis", false, true)
@ -348,6 +363,9 @@ namespace {
const DataLayout *DL;
/// An optional DT pointer.
DominatorTree *DT;
/// A counter to record how many times Overdefined has been tried to be
/// lowered.
DenseMap<BasicBlock *, unsigned> LoweringOverdefinedTimes;
friend struct LVIValueHandle;
@ -480,6 +498,9 @@ void LazyValueInfoCache::eraseBlock(BasicBlock *BB) {
}
void LazyValueInfoCache::solve() {
// Reset the counter of lowering overdefined value.
LoweringOverdefinedTimes.clear();
while (!BlockValueStack.empty()) {
std::pair<BasicBlock*, Value*> &e = BlockValueStack.top();
if (solveBlockValue(e.second, e.first)) {
@ -539,8 +560,16 @@ bool LazyValueInfoCache::solveBlockValue(Value *Val, BasicBlock *BB) {
// BB2. So we should have to follow data flow propagation algorithm to get the
// value on edge BB1->BB2 propagated to BB2, and finally %v on BB2 has a
// constant range describing a negative value.
//
// In the mean time, limit the number of additional lowering lattice value to
// avoid unjustified memory grows.
if (!BBLV.isUndefined() && !BBLV.isOverdefined()) {
if (LoweringOverdefinedTimes.count(BB) == 0)
LoweringOverdefinedTimes.insert(std::make_pair(BB, 0));
if ((!BBLV.isUndefined() && !BBLV.isOverdefined()) ||
(BBLV.isOverdefined() &&
(LoweringOverdefinedTimes[BB] > OverdefinedThreshold ||
LoweringOverdefinedTimes.size() > OverdefinedBBThreshold))) {
DEBUG(dbgs() << " reuse BB '" << BB->getName() << "' val=" << BBLV <<'\n');
// Since we're reusing a cached value here, we don't need to update the
@ -554,6 +583,7 @@ bool LazyValueInfoCache::solveBlockValue(Value *Val, BasicBlock *BB) {
// lattice value to overdefined, so that cycles will terminate and be
// conservatively correct.
BBLV.markOverdefined();
++LoweringOverdefinedTimes[BB];
Instruction *BBI = dyn_cast<Instruction>(Val);
if (!BBI || BBI->getParent() != BB) {