[llvm] [HashRecognize] Strip ValueEvolution (PR #148620)

[Piotr Fusik via llvm-commits]

================
@@ -73,202 +73,31 @@ using namespace SCEVPatternMatch;
 
 #define DEBUG_TYPE "hash-recognize"
 
-// KnownBits for a PHI node. There are at most two PHI nodes, corresponding to
-// the Simple Recurrence and Conditional Recurrence. The IndVar PHI is not
-// relevant.
-using KnownPhiMap = SmallDenseMap<const PHINode *, KnownBits, 2>;
-
-// A pair of a PHI node along with its incoming value from within a loop.
-using PhiStepPair = std::pair<const PHINode *, const Instruction *>;
-
-/// A much simpler version of ValueTracking, in that it computes KnownBits of
-/// values, except that it computes the evolution of KnownBits in a loop with a
-/// given trip count, and predication is specialized for a significant-bit
-/// check.
-class ValueEvolution {
-  const unsigned TripCount;
-  const bool ByteOrderSwapped;
-  APInt GenPoly;
-  StringRef ErrStr;
-
-  // Compute the KnownBits of a BinaryOperator.
-  KnownBits computeBinOp(const BinaryOperator *I);
-
-  // Compute the KnownBits of an Instruction.
-  KnownBits computeInstr(const Instruction *I);
-
-  // Compute the KnownBits of a Value.
-  KnownBits compute(const Value *V);
-
-public:
-  // ValueEvolution is meant to be constructed with the TripCount of the loop,
-  // and a boolean indicating whether the polynomial algorithm is big-endian
-  // (for the significant-bit check).
-  ValueEvolution(unsigned TripCount, bool ByteOrderSwapped);
-
-  // Given a list of PHI nodes along with their incoming value from within the
-  // loop, computeEvolutions computes the KnownBits of each of the PHI nodes on
-  // the final iteration. Returns true on success and false on error.
-  bool computeEvolutions(ArrayRef<PhiStepPair> PhiEvolutions);
-
-  // In case ValueEvolution encounters an error, this is meant to be used for a
-  // precise error message.
-  StringRef getError() const { return ErrStr; }
-
-  // A set of Instructions visited by ValueEvolution. The only unvisited
-  // instructions will be ones not on the use-def chain of the PHIs' evolutions.
+/// Checks that all instructions reachable from \p Roots on the use-def chain
+/// are contained within loop \p L, and that that are no stray instructions in
+/// the loop not visited by the use-def walk.
----------------
pfusik wrote:

```suggestion
/// Checks if there's a stray instruction in the loop \p L
/// outside of the use-def chains from \p Roots,
/// or we escape the loop during the use-def walk.
```
Either that, or flip the returned value.

https://github.com/llvm/llvm-project/pull/148620