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[Dominators] Simplify child lists and make them deterministic

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This fixes an extremely subtle non-determinism that can only be
triggered by an unfortunate alignment of passes. In my case:

- JumpThreading does large dominator tree updates
- CorrelatedValuePropagation preserves domtree now
- LICM codegen depends on the order of children on domtree nodes

The last part is non-deterministic if the update was stored in a set.
But it turns out that the set is completely unnecessary, updates are
deduplicated at an earlier stage so we can just use a vector, which is
both more efficient and doesn't destroy the input ordering.

I didn't manage to get the 240 MB IR file reduced enough, triggering
this bug requires a lot of jump threading, so landing this without a
test case.

Differential Revision: https://reviews.llvm.org/D48392

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@335176 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer 2018-06-20 21:12:59 +00:00
parent af6c3e6dec
commit b8b321ac76
1 changed files with 12 additions and 7 deletions
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19
include/llvm/Support/GenericDomTreeConstruction.h
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@ -82,8 +82,8 @@ struct SemiNCAInfo {
// Note that these children are from the future relative to what the
// DominatorTree knows about -- using them to gets us some snapshot of the
// CFG from the past (relative to the state of the CFG).
DenseMap<NodePtr, SmallDenseSet<NodePtrAndKind, 4>> FutureSuccessors;
DenseMap<NodePtr, SmallDenseSet<NodePtrAndKind, 4>> FuturePredecessors;
DenseMap<NodePtr, SmallVector<NodePtrAndKind, 4>> FutureSuccessors;
DenseMap<NodePtr, SmallVector<NodePtrAndKind, 4>> FuturePredecessors;
// Remembers if the whole tree was recalculated at some point during the
// current batch update.
bool IsRecalculated = false;
@ -1176,8 +1176,8 @@ struct SemiNCAInfo {
// predecessors. Note that these sets will only decrease size over time, as
// the next CFG snapshots slowly approach the actual (current) CFG.
for (UpdateT &U : BUI.Updates) {
BUI.FutureSuccessors[U.getFrom()].insert({U.getTo(), U.getKind()});
BUI.FuturePredecessors[U.getTo()].insert({U.getFrom(), U.getKind()});
BUI.FutureSuccessors[U.getFrom()].push_back({U.getTo(), U.getKind()});
BUI.FuturePredecessors[U.getTo()].push_back({U.getFrom(), U.getKind()});
}
LLVM_DEBUG(dbgs() << "About to apply " << NumLegalized << " updates\n");
@ -1265,13 +1265,18 @@ struct SemiNCAInfo {
LLVM_DEBUG(dbgs() << "Applying update: " << CurrentUpdate << "\n");
// Move to the next snapshot of the CFG by removing the reverse-applied
// current update.
// current update. Since updates are performed in the same order they are
// legalized it's sufficient to pop the last item here.
auto &FS = BUI.FutureSuccessors[CurrentUpdate.getFrom()];
FS.erase({CurrentUpdate.getTo(), CurrentUpdate.getKind()});
assert(FS.back().getPointer() == CurrentUpdate.getTo() &&
FS.back().getInt() == CurrentUpdate.getKind());
FS.pop_back();
if (FS.empty()) BUI.FutureSuccessors.erase(CurrentUpdate.getFrom());
auto &FP = BUI.FuturePredecessors[CurrentUpdate.getTo()];
FP.erase({CurrentUpdate.getFrom(), CurrentUpdate.getKind()});
assert(FP.back().getPointer() == CurrentUpdate.getFrom() &&
FP.back().getInt() == CurrentUpdate.getKind());
FP.pop_back();
if (FP.empty()) BUI.FuturePredecessors.erase(CurrentUpdate.getTo());
if (CurrentUpdate.getKind() == UpdateKind::Insert)