[llvm] Reland "Redesign Straight-Line Strength Reduction (SLSR) (#162930)" (PR #169614)

[Artem Belevich via llvm-commits]

================
@@ -677,61 +688,37 @@ void StraightLineStrengthReduce::setBasisAndDeltaFor(Candidate &C) {
     return false;
   };
 
-  // Priority:
-  // Constant Delta from Index > Constant Delta from Base >
-  // Constant Delta from Stride > Variable Delta from Base or Stride
-  // TODO: Change the priority to align with the cost model.
-
-  // First, look for a constant index-diff basis
-  if (const auto *IndexDeltaCandidates =
-          CandidateDict.getCandidatesWithDeltaKind(C, Candidate::IndexDelta)) {
-    bool FoundConstDelta =
-        SearchFrom(*IndexDeltaCandidates, [&DT = DT, &C](Candidate *Basis) {
-          if (isSimilar(C, *Basis, Candidate::IndexDelta)) {
-            assert(DT->dominates(Basis->Ins, C.Ins));
-            auto *Delta = getIndexDelta(C, *Basis);
-            if (!C.isProfitableRewrite(Delta, Candidate::IndexDelta))
-              return false;
-            C.Basis = Basis;
-            C.DeltaKind = Candidate::IndexDelta;
-            C.Delta = Delta;
-            LLVM_DEBUG(dbgs() << "Found delta from Index " << *C.Delta << "\n");
-            return true;
-          }
-          return false;
-        });
-    if (FoundConstDelta)
-      return;
-  }
-
-  // No constant-index-diff basis found. look for the best possible base-diff
-  // or stride-diff basis
-  // Base/Stride diffs not supported for form (B + i) * S
-  if (C.CandidateKind == Candidate::Mul)
-    return;
-
   auto For = [this, &C](Candidate::DKind K) {
     // return true if find a Basis with constant delta and stop searching,
     // return false if did not find a Basis or the delta is not a constant
     // and continue searching for a Basis with constant delta
----------------
Artem-B wrote:

Nit: Outside of the returned lambda, the comment misses "return a lambda predicate that...". 

Alternatively, moving the comments inside of the inner lambda would work, too.

https://github.com/llvm/llvm-project/pull/169614