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Fix handling of unreachable blocks in the SSAUpdater. The previous code only

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handled cases where a block had zero predecessors, but failed to detect other
cases like loops with no entries.  The SSAUpdater is already doing a forward
traversal through the blocks, so it is not hard to identify the blocks that
were never reached on that traversal.  This fixes the crash for ppc on the
stepanov_vector test.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@103184 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bob Wilson 2010-05-06 16:24:11 +00:00
parent 429009b0f1
commit c52edc7d30
1 changed files with 29 additions and 23 deletions
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52
include/llvm/Transforms/Utils/SSAUpdaterImpl.h
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@ -69,7 +69,7 @@ public:
/// where needed.
ValT GetValue(BlkT *BB) {
SmallVector<BBInfo*, 100> BlockList;
BuildBlockList(BB, &BlockList);
BBInfo *PseudoEntry = BuildBlockList(BB, &BlockList);
// Special case: bail out if BB is unreachable.
if (BlockList.size() == 0) {
@ -78,7 +78,7 @@ public:
return V;
}
FindDominators(&BlockList);
FindDominators(&BlockList, PseudoEntry);
FindPHIPlacement(&BlockList);
FindAvailableVals(&BlockList);
@ -89,7 +89,7 @@ public:
/// through its predecessors until reaching blocks with known values.
/// Create BBInfo structures for the blocks and append them to the block
/// list.
void BuildBlockList(BlkT *BB, BlockListTy *BlockList) {
BBInfo *BuildBlockList(BlkT *BB, BlockListTy *BlockList) {
SmallVector<BBInfo*, 10> RootList;
SmallVector<BBInfo*, 64> WorkList;
@ -106,17 +106,12 @@ public:
Preds.clear();
Traits::FindPredecessorBlocks(Info->BB, &Preds);
Info->NumPreds = Preds.size();
Info->Preds = static_cast<BBInfo**>
(Allocator.Allocate(Info->NumPreds * sizeof(BBInfo*),
AlignOf<BBInfo*>::Alignment));
// Treat an unreachable predecessor as a definition with 'undef'.
if (Info->NumPreds == 0) {
Info->AvailableVal = Traits::GetUndefVal(Info->BB, Updater);
Info->DefBB = Info;
RootList.push_back(Info);
continue;
}
if (Info->NumPreds == 0)
Info->Preds = 0;
else
Info->Preds = static_cast<BBInfo**>
(Allocator.Allocate(Info->NumPreds * sizeof(BBInfo*),
AlignOf<BBInfo*>::Alignment));
for (unsigned p = 0; p != Info->NumPreds; ++p) {
BlkT *Pred = Preds[p];
@ -187,6 +182,7 @@ public:
}
}
PseudoEntry->BlkNum = BlkNum;
return PseudoEntry;
}
/// IntersectDominators - This is the dataflow lattice "meet" operation for
@ -219,7 +215,7 @@ public:
/// of root nodes for blocks that define the value. The dominators for this
/// subset CFG are not the standard dominators but they are adequate for
/// placing PHIs within the subset CFG.
void FindDominators(BlockListTy *BlockList) {
void FindDominators(BlockListTy *BlockList, BBInfo *PseudoEntry) {
bool Changed;
do {
Changed = false;
@ -227,19 +223,29 @@ public:
for (typename BlockListTy::reverse_iterator I = BlockList->rbegin(),
E = BlockList->rend(); I != E; ++I) {
BBInfo *Info = *I;
BBInfo *NewIDom = 0;
// Start with the first predecessor.
assert(Info->NumPreds > 0 && "unreachable block");
BBInfo *NewIDom = Info->Preds[0];
// Iterate through the block's other predecessors.
for (unsigned p = 1; p != Info->NumPreds; ++p) {
// Iterate through the block's predecessors.
for (unsigned p = 0; p != Info->NumPreds; ++p) {
BBInfo *Pred = Info->Preds[p];
NewIDom = IntersectDominators(NewIDom, Pred);
// Treat an unreachable predecessor as a definition with 'undef'.
if (Pred->BlkNum == 0) {
Pred->AvailableVal = Traits::GetUndefVal(Pred->BB, Updater);
(*AvailableVals)[Pred->BB] = Pred->AvailableVal;
Pred->DefBB = Pred;
Pred->BlkNum = PseudoEntry->BlkNum;
PseudoEntry->BlkNum++;
}
if (!NewIDom)
NewIDom = Pred;
else
NewIDom = IntersectDominators(NewIDom, Pred);
}
// Check if the IDom value has changed.
if (NewIDom != Info->IDom) {
if (NewIDom && NewIDom != Info->IDom) {
Info->IDom = NewIDom;
Changed = true;
}