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

[Karthika Devi C 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.
+///
+/// NOTE: This assumes independent blocks and breaks otherwise.
----------------
kartcq wrote:

In line 2704, we check for all the binary instructions using this UsedOutsideBlock function as well.

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