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UseListOrder: Fix undefined behaviour
This commit fixes undefined behaviour that caused the revert in r214249. The problem was two unsequenced operations on a `DenseMap<>`, giving different behaviour in GCC and Clang. This: DenseMap<T*, unsigned> DM; for (auto &X : ...) DM[&X] = DM.size() + 1; should have been: DenseMap<T*, unsigned> DM; for (auto &X : ...) { unsigned Size = DM.size(); DM[&X] = Size + 1; } Until r214242, this difference between compilers didn't matter. In r214242, `OrderMap::LastGlobalValueID` was introduced and compared against IDs, which in GCC were off-by-one my expectations. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214270 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -34,6 +34,11 @@ struct OrderMap {
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std::pair<unsigned, bool> lookup(const Value *V) const {
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return IDs.lookup(V);
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}
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void index(const Value *V) {
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// Explicitly sequence get-size and insert-value operations to avoid UB.
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unsigned ID = IDs.size() + 1;
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IDs[V].first = ID;
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}
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};
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}
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@ -48,8 +53,8 @@ static void orderValue(const Value *V, OrderMap &OM) {
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orderValue(Op, OM);
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// Note: we cannot cache this lookup above, since inserting into the map
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// changes the map's size, and thus affects the ID.
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OM[V].first = OM.size() + 1;
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// changes the map's size, and thus affects the other IDs.
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OM.index(V);
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}
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static OrderMap orderModule(const Module *M) {
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