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[DFAJumpThreading] make update order deterministic 

We tracked down some non-determinism in compilation output to the
DFAJumpThreading pass. These changes fixed our issue:

* Make the DefMap type a MapVector to make its iteration order depend on
  insertion order.
* Sort the values to be inserted into NewDefs by instruction order to
  make the insertion order deterministic. Since these values come from
  iterating over a ValueMap, which doesn't have deterministic iteration
  order, I couldn't fix this at its source.

Reviewed By: alexey.zhikhar

Differential Revision: https://reviews.llvm.org/D118590
This commit is contained in:
Olle Fredriksson 2022-02-01 11:01:15 -05:00 committed by Alex Zhikhartsev
parent 22d3bbdf4e
commit 9d555b4a83
1 changed files with 15 additions and 5 deletions
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20
llvm/lib/Transforms/Scalar/DFAJumpThreading.cpp
View File

@ -357,7 +357,7 @@ typedef DenseMap<BasicBlock *, CloneList> DuplicateBlockMap;
// This map keeps track of all the new definitions for an instruction. This
// information is needed when restoring SSA form after cloning blocks.
typedef DenseMap<Instruction *, std::vector<Instruction *>> DefMap;
typedef MapVector<Instruction *, std::vector<Instruction *>> DefMap;
inline raw_ostream &operator<<(raw_ostream &OS, const PathType &Path) {
OS << "< ";
@ -1126,6 +1126,9 @@ private:
/// Add new value mappings to the DefMap to keep track of all new definitions
/// for a particular instruction. These will be used while updating SSA form.
void updateDefMap(DefMap &NewDefs, ValueToValueMapTy &VMap) {
SmallVector<std::pair<Instruction *, Instruction *>> NewDefsVector;
NewDefsVector.reserve(VMap.size());
for (auto Entry : VMap) {
Instruction *Inst =
dyn_cast<Instruction>(const_cast<Value *>(Entry.first));
@ -1138,11 +1141,18 @@ private:
if (!Cloned)
continue;
if (NewDefs.find(Inst) == NewDefs.end())
NewDefs[Inst] = {Cloned};
else
NewDefs[Inst].push_back(Cloned);
NewDefsVector.push_back({Inst, Cloned});
}
// Sort the defs to get deterministic insertion order into NewDefs.
sort(NewDefsVector, [](const auto &LHS, const auto &RHS) {
if (LHS.first == RHS.first)
return LHS.second->comesBefore(RHS.second);
return LHS.first->comesBefore(RHS.first);
});
for (const auto &KV : NewDefsVector)
NewDefs[KV.first].push_back(KV.second);
}
/// Update the last branch of a particular cloned path to point to the correct