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Somehow I was getting reasonable results for the test cases I was interested 

in despite not ever incrementing any path costs, so that the only nonzero costs
arose from the all-left path in the first column.  Anyway.  Perform the diff
starting from the beginning of the block to avoid capturing (say) loads of
allocas.

Vastly improves diff results on code that hasn't been mem2reg'ed.

llvm-svn: 109741
This commit is contained in:
John McCall 2010-07-29 08:53:59 +00:00
parent 10c91bfa66
commit d293c4e6e0
1 changed files with 38 additions and 14 deletions
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52
llvm/tools/llvm-diff/DifferenceEngine.cpp
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@ -124,7 +124,7 @@ class FunctionDifferenceEngine {
/// The current mapping from old blocks to new blocks.
DenseMap<BasicBlock*, BasicBlock*> Blocks;
DenseSet<std::pair<Value*, Value*> > TentativeValuePairs;
DenseSet<std::pair<Value*, Value*> > TentativeValues;
unsigned getUnprocPredCount(BasicBlock *Block) const {
unsigned Count = 0;
@ -186,22 +186,32 @@ class FunctionDifferenceEngine {
BasicBlock::iterator LI = L->begin(), LE = L->end();
BasicBlock::iterator RI = R->begin(), RE = R->end();
llvm::SmallVector<std::pair<Instruction*,Instruction*>, 20> TentativePairs;
do {
assert(LI != LE && RI != RE);
Instruction *LeftI = &*LI, *RightI = &*RI;
// If the instructions differ, start the more sophisticated diff
// algorithm here.
if (diff(LeftI, RightI, false, true))
return runBlockDiff(LI, RI);
// algorithm at the start of the block.
if (diff(LeftI, RightI, false, true)) {
TentativeValues.clear();
return runBlockDiff(L->begin(), R->begin());
}
// Otherwise, unify them.
// Otherwise, tentatively unify them.
if (!LeftI->use_empty())
Values[LeftI] = RightI;
TentativeValues.insert(std::make_pair(LeftI, RightI));
++LI, ++RI;
} while (LI != LE); // This is sufficient: we can't get equality of
// terminators if there are residual instructions.
// Make all the tentative pairs solid.
for (llvm::DenseSet<std::pair<Value*,Value*> >::iterator
I = TentativeValues.begin(), E = TentativeValues.end(); I != E; ++I)
Values[I->first] = I->second;
TentativeValues.clear();
}
bool matchForBlockDiff(Instruction *L, Instruction *R);
@ -417,7 +427,7 @@ class FunctionDifferenceEngine {
return equivalentAsOperands(cast<Constant>(L), cast<Constant>(R));
if (isa<Instruction>(L))
return Values[L] == R || TentativeValuePairs.count(std::make_pair(L, R));
return Values[L] == R || TentativeValues.count(std::make_pair(L, R));
if (isa<Argument>(L))
return Values[L] == R;
@ -477,11 +487,15 @@ void FunctionDifferenceEngine::runBlockDiff(BasicBlock::iterator LStart,
DiffEntry *Cur = Paths1.data();
DiffEntry *Next = Paths2.data();
assert(TentativeValuePairs.empty());
const unsigned LeftCost = 2;
const unsigned RightCost = 2;
const unsigned MatchCost = 0;
assert(TentativeValues.empty());
// Initialize the first column.
for (unsigned I = 0; I != NL+1; ++I) {
Cur[I].Cost = I;
Cur[I].Cost = I * LeftCost;
for (unsigned J = 0; J != I; ++J)
Cur[I].Path.push_back(DifferenceEngine::DC_left);
}
@ -489,19 +503,23 @@ void FunctionDifferenceEngine::runBlockDiff(BasicBlock::iterator LStart,
for (BasicBlock::iterator RI = RStart; RI != RE; ++RI) {
// Initialize the first row.
Next[0] = Cur[0];
Next[0].Cost += RightCost;
Next[0].Path.push_back(DifferenceEngine::DC_right);
unsigned Index = 1;
for (BasicBlock::iterator LI = LStart; LI != LE; ++LI, ++Index) {
if (matchForBlockDiff(&*LI, &*RI)) {
Next[Index] = Cur[Index-1];
Next[Index].Cost += MatchCost;
Next[Index].Path.push_back(DifferenceEngine::DC_match);
TentativeValuePairs.insert(std::make_pair(&*LI, &*RI));
TentativeValues.insert(std::make_pair(&*LI, &*RI));
} else if (Next[Index-1].Cost <= Cur[Index].Cost) {
Next[Index] = Next[Index-1];
Next[Index].Cost += LeftCost;
Next[Index].Path.push_back(DifferenceEngine::DC_left);
} else {
Next[Index] = Cur[Index];
Next[Index].Cost += RightCost;
Next[Index].Path.push_back(DifferenceEngine::DC_right);
}
}
@ -518,15 +536,21 @@ void FunctionDifferenceEngine::runBlockDiff(BasicBlock::iterator LStart,
while (Path.back() == DifferenceEngine::DC_match)
Path.pop_back();
for (SmallVectorImpl<char>::iterator
PI = Path.begin(), PE = Path.end(); PI != PE; ++PI) {
// Skip leading matches.
SmallVectorImpl<char>::iterator
PI = Path.begin(), PE = Path.end();
while (PI != PE && *PI == DifferenceEngine::DC_match)
++PI, ++LI, ++RI;
for (; PI != PE; ++PI) {
switch (static_cast<DifferenceEngine::DiffChange>(*PI)) {
case DifferenceEngine::DC_match:
assert(LI != LE && RI != RE);
{
Instruction *L = &*LI, *R = &*RI;
DifferenceEngine::Context C(Engine, L, R);
diff(L, R, false, true);
diff(L, R, false, true); // unify successors
Values[L] = R; // make non-tentative
Diff.addMatch(L, R);
}
++LI; ++RI;
@ -546,7 +570,7 @@ void FunctionDifferenceEngine::runBlockDiff(BasicBlock::iterator LStart,
}
}
TentativeValuePairs.clear();
TentativeValues.clear();
}
}