[polly] [Polly] Data flow reduction detection to cover more cases (PR #84901)

[Michael Kruse via llvm-commits]

================
@@ -2568,49 +2579,196 @@ bool checkCandidatePairAccesses(MemoryAccess *LoadMA, MemoryAccess *StoreMA,
     // Finally, check if they are no other instructions accessing this memory
     isl::map AllAccsRel = LoadAccs.unite(StoreAccs);
     AllAccsRel = AllAccsRel.intersect_domain(Domain);
+
     isl::set AllAccs = AllAccsRel.range();
+
     Valid = !hasIntersectingAccesses(AllAccs, LoadMA, StoreMA, Domain, MemAccs);
 
     LLVM_DEBUG(dbgs() << " == The accessed memory is " << (Valid ? "not " : "")
                       << "accessed by other instructions!\n");
   }
+
   return Valid;
 }
 
-void ScopBuilder::checkForReductions(ScopStmt &Stmt) {
-  SmallVector<MemoryAccess *, 2> Loads;
-  SmallVector<std::pair<MemoryAccess *, MemoryAccess *>, 4> Candidates;
+/// Perform a data flow analysis on the current basic block to propagate the
+/// uses of loaded values. Then check and mark the memory accesses which are
+/// part of reduction like chains.
----------------
Meinersbur wrote:

`checkForReductions` already has a Doxygen comment (`///`) in the header. If this is meant to document what the result of the method call is, then the header comment should be updated. If this is meant to describe the algorithm how it is implemented, it should go as a standard comment (`//`) into the body.

https://github.com/llvm/llvm-project/pull/84901