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

[Drew Kersnar via llvm-commits]

================
@@ -177,22 +203,164 @@ class StraightLineStrengthReduce {
     // Points to the immediate basis of this candidate, or nullptr if we cannot
     // find any basis for this candidate.
     Candidate *Basis = nullptr;
+
+    DKind DeltaKind = InvalidDelta;
+
+    // Store SCEV of Stride to compute delta from different strides
+    const SCEV *StrideSCEV = nullptr;
+
+    // Points to (Y - X) that will be used to rewrite this candidate.
+    Value *Delta = nullptr;
+
+    /// Cost model: Evaluate the computational efficiency of the candidate.
+    ///
+    /// Efficiency levels (higher is better):
+    ///   ZeroInst (5) - [Variable] or [Const]
+    ///   OneInstOneVar (4) - [Variable + Const] or [Variable * Const]
+    ///   OneInstTwoVar (3) - [Variable + Variable] or [Variable * Variable]
+    ///   TwoInstOneVar (2) - [Const + Const * Variable]
+    ///   TwoInstTwoVar (1) - [Variable + Const * Variable]
+    enum EfficiencyLevel : unsigned {
+      Unknown = 0,
+      TwoInstTwoVar = 1,
+      TwoInstOneVar = 2,
+      OneInstTwoVar = 3,
+      OneInstOneVar = 4,
+      ZeroInst = 5
+    };
+
+    static EfficiencyLevel
+    getComputationEfficiency(Kind CandidateKind, const ConstantInt *Index,
+                             const Value *Stride, const SCEV *Base = nullptr) {
+      bool IsConstantBase = false;
+      bool IsZeroBase = false;
+      // When evaluating the efficiency of a rewrite, if the Basis's SCEV is
----------------
dakersnar wrote:

```suggestion
      // When evaluating the efficiency of a rewrite, if the Base's SCEV is
```

Typo, right?

https://github.com/llvm/llvm-project/pull/162930