[polly] [Polly] Distribute the innermost point loop of tile over its statements (PR #225844)

[Michael Kruse via llvm-commits]

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@@ -548,6 +576,161 @@ ScheduleTreeOptimizer::applyTileBandOpt(isl::schedule_node Node) {
   return Node;
 }
 
+isl::schedule_node
+ScheduleTreeOptimizer::distributeInnermostLoop(isl::schedule_node Node,
+                                               const Dependences *D) {
+  // This runs within a quota of isl operations. Every isl result that is used
+  // in a condition, iterated over or dereferenced is checked for an error
+  // first; in that case the band is left as it is.
+  if (Node.is_null() || !isSimpleInnermostBand(Node))
+    return Node;
+
+  isl::union_set Domain = Node.get_domain();
+  if (Domain.is_null())
+    return Node;
+  isl::set_list DomainList = Domain.get_set_list();
+  if (DomainList.is_null())
+    return Node;
+  SmallVector<std::pair<ScopStmt *, isl::set>, 8> Stmts;
+  for (isl::set Set : DomainList) {
+    isl::id Id = Set.get_tuple_id();
+    if (Id.is_null())
+      return Node;
+    auto *Stmt = static_cast<ScopStmt *>(Id.get_user());
+    if (!Stmt)
+      return Node;
+    Stmts.push_back({Stmt, Set});
+  }
+  unsigned NumStmts = Stmts.size();
+  if (NumStmts < 2)
+    return Node;
+
+  // Number the statements in the order of Scop::Stmts, so that the result does
+  // not depend on the order in which isl lists them.
+  DenseMap<const ScopStmt *, unsigned> ScopOrder;
+  for (const ScopStmt &Stmt : *Stmts.front().first->getParent())
+    ScopOrder.insert({&Stmt, ScopOrder.size()});
+  llvm::sort(Stmts, [&](const auto &A, const auto &B) {
+    return ScopOrder.lookup(A.first) < ScopOrder.lookup(B.first);
+  });
+  DenseMap<const ScopStmt *, unsigned> StmtIndex;
+  for (auto [Idx, Stmt] : enumerate(Stmts))
+    StmtIndex[Stmt.first] = Idx;
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Meinersbur wrote:

Could you add a comment on why not using the `ScopOrder` Idx already available?

https://github.com/llvm/llvm-project/pull/225844