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Make IsValueFullyAvailableInBlock safe.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60588 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2008-12-05 07:49:08 +00:00
parent 7f50863e52
commit 72bc70d499
1 changed files with 60 additions and 14 deletions
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74
lib/Transforms/Scalar/GVN.cpp
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@ -1,4 +1,4 @@
//===- GVN.cpp - Eliminate redundant values and loads ------------===//
//===- GVN.cpp - Eliminate redundant values and loads ---------------------===//
//
// The LLVM Compiler Infrastructure
//
@ -47,7 +47,7 @@ STATISTIC(NumPRELoad, "Number of loads PRE'd");
static cl::opt<bool> EnablePRE("enable-pre",
cl::init(true), cl::Hidden);
cl::opt<bool> EnableLoadPRE("enable-load-pre");
cl::opt<bool> EnableLoadPRE("enable-load-pre"/*, cl::init(true)*/);
//===----------------------------------------------------------------------===//
// ValueTable Class
@ -867,34 +867,79 @@ Value *GVN::GetValueForBlock(BasicBlock *BB, LoadInst* orig,
/// IsValueFullyAvailableInBlock - Return true if we can prove that the value
/// we're analyzing is fully available in the specified block. As we go, keep
/// track of which blocks we know it is fully alive or not in
/// FullyAvailableBlocks.
/// track of which blocks we know are fully alive in FullyAvailableBlocks. This
/// map is actually a tri-state map with the following values:
/// 0) we know the block *is not* fully available.
/// 1) we know the block *is* fully available.
/// 2) we do not know whether the block is fully available or not, but we are
/// currently speculating that it will be.
/// 3) we are speculating for this block and have used that to speculate for
/// other blocks.
static bool IsValueFullyAvailableInBlock(BasicBlock *BB,
DenseMap<BasicBlock*, bool> &FullyAvailableBlocks) {
DenseMap<BasicBlock*, char> &FullyAvailableBlocks) {
// Optimistically assume that the block is fully available and check to see
// if we already know about this block in one lookup.
std::pair<DenseMap<BasicBlock*, bool>::iterator, bool> IV =
FullyAvailableBlocks.insert(std::make_pair(BB, true));
std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV =
FullyAvailableBlocks.insert(std::make_pair(BB, 2));
// If the entry already existed for this block, return the precomputed value.
if (!IV.second)
return IV.first->second;
if (!IV.second) {
// If this is a speculative "available" value, mark it as being used for
// speculation of other blocks.
if (IV.first->second == 2)
IV.first->second = 3;
return IV.first->second != 0;
}
// Otherwise, see if it is fully available in all predecessors.
pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
// If this block has no predecessors, it isn't live-in here.
if (PI == PE)
return FullyAvailableBlocks[BB] = false;
goto SpeculationFailure;
for (; PI != PE; ++PI)
// If the value isn't fully available in one of our predecessors, then it
// isn't fully available in this block either. Undo our previous
// optimistic assumption and bail out.
if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks))
return FullyAvailableBlocks[BB] = false;
goto SpeculationFailure;
return true;
// SpeculationFailure - If we get here, we found out that this is not, after
// all, a fully-available block. We have a problem if we speculated on this and
// used the speculation to mark other blocks as available.
SpeculationFailure:
char &BBVal = FullyAvailableBlocks[BB];
// If we didn't speculate on this, just return with it set to false.
if (BBVal == 2) {
BBVal = 0;
return false;
}
// If we did speculate on this value, we could have blocks set to 1 that are
// incorrect. Walk the (transitive) successors of this block and mark them as
// 0 if set to one.
SmallVector<BasicBlock*, 32> BBWorklist;
BBWorklist.push_back(BB);
while (!BBWorklist.empty()) {
BasicBlock *Entry = BBWorklist.pop_back_val();
// Note that this sets blocks to 0 (unavailable) if they happen to not
// already be in FullyAvailableBlocks. This is safe.
char &EntryVal = FullyAvailableBlocks[Entry];
if (EntryVal == 0) continue; // Already unavailable.
// Mark as unavailable.
EntryVal = 0;
for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I)
BBWorklist.push_back(*I);
}
return false;
}
/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are
@ -1047,7 +1092,7 @@ bool GVN::processNonLocalLoad(LoadInst *LI,
// that one block.
BasicBlock *UnavailablePred = 0;
DenseMap<BasicBlock*, bool> FullyAvailableBlocks;
DenseMap<BasicBlock*, char> FullyAvailableBlocks;
for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i)
FullyAvailableBlocks[ValuesPerBlock[i].first] = true;
for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i)
@ -1086,11 +1131,11 @@ bool GVN::processNonLocalLoad(LoadInst *LI,
<< UnavailablePred->getName() << "': " << *LI);
return false;
}
// Okay, we can eliminate this load by inserting a reload in the predecessor
// and using PHI construction to get the value in the other predecessors, do
// it.
DEBUG(cerr << "GVN REMOVING PRE LOAD: " << *LI);
/*DEBUG*/(cerr << "GVN REMOVING PRE LOAD: " << *LI);
Value *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false,
LI->getAlignment(),
@ -1103,6 +1148,7 @@ bool GVN::processNonLocalLoad(LoadInst *LI,
// Perform PHI construction.
Value* v = GetValueForBlock(LI->getParent(), LI, BlockReplValues, true);
LI->replaceAllUsesWith(v);
v->takeName(LI);
toErase.push_back(LI);
NumPRELoad++;
return true;