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[PM] Use PoisoningVH correctly when merely deleting entries in a map

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with it.

This code was dereferencing the PoisoningVH which isn't allowed once it
is poisoned. But the code itself really doesn't need to access the
pointer, it is just doing the safe stuff of clearing out data structures
keyed on the pointer value.

Change the code to use iterators to erase directly from a DenseMap. This
is also substantially more efficient as it avoids lots of hashing and
lookups to do the erasure. DenseMap supports iterating behind the
iteration which is fairly easy to implement.

Sadly, I don't have a test case here. I'm not even close and I don't
know that I ever will be. The issue is that several of the tricky
aspects of fixing this only show up when you cause the stack's
SmallVector to be in *EXACTLY* the right location. I only ever got
a reproduction for those with Clang, and only with *exactly* the right
command line flags. Any adjustment, even to seemingly unrelated flags,
would make partial and half-way solutions magically start to "work". In
good news, all of this was caught with the LLVM test suite. Also, there
is no *specific* code here that is untested, just that the old pattern
of code won't immediately fail on any test case I've managed to
contrive.

llvm-svn: 293160
This commit is contained in:
Chandler Carruth 2017-01-26 08:31:54 +00:00
parent a86dd54b5e
commit 579549a336
1 changed files with 6 additions and 6 deletions
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12
lib/Analysis/LazyValueInfo.cpp
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@ -459,15 +459,15 @@ namespace {
}
void LazyValueInfoCache::eraseValue(Value *V) {
SmallVector<AssertingVH<BasicBlock>, 4> ToErase;
for (auto &I : OverDefinedCache) {
SmallPtrSetImpl<Value *> &ValueSet = I.second;
for (auto I = OverDefinedCache.begin(), E = OverDefinedCache.end(); I != E;) {
// Copy and increment the iterator immediately so we can erase behind
// ourselves.
auto Iter = I++;
SmallPtrSetImpl<Value *> &ValueSet = Iter->second;
ValueSet.erase(V);
if (ValueSet.empty())
ToErase.push_back(&*I.first);
OverDefinedCache.erase(Iter);
}
for (auto &BB : ToErase)
OverDefinedCache.erase(&*BB);
ValueCache.erase(V);
}