[mlir][linalg][bufferize] Rewrite conflict detection

For each memory read, follow SSA use-def chains to find the op that produces the data being read (i.e., the most recent write). A memory write to an alias is a conflict if it takes places after the "most recent write" but before the read.

This CL introduces two main changes:
* There is a concise definition of a conflict. Given a piece of IR with InPlaceSpec annotations and a computes alias set, it is easy to compute whether this program has a conflict. No need to consider multiple cases such as "read of operand after in-place write" etc.
* No need to check for clobbering.

Differential Revision: https://reviews.llvm.org/D111287

Author: matthias-springer

mlir/include/mlir/Dialect/Linalg/Transforms/ComprehensiveBufferize.h

@@ -71,44 +71,19 @@ class BufferizationAliasInfo {
   /// Set the inPlace bufferization spec to false.
   void bufferizeOutOfPlace(OpResult result);
 
-  /// Return true if it is possible to find an inplace write W among `usesWrite`
-  /// and a read R among `usesRead`, such that W and R interfere.
-  /// Such a (W, R) pair is an interference to the inplace bufferization of
-  /// opResult when:
-  ///   1. R is not known properly dominate W (i.e. the effects of the write may
-  ///      be visible from R).
-  ///   2. one cannot find an intermediate clobbering write `C` to W, such that
-  ///      C interleaved between W and R (i.e. W -> C -> R where -> denotes
-  ///      dominance).
-  bool wouldCreateReadAfterWriteInterference(
-      Operation *opToBufferize, DenseSet<OpOperand *> &usesRead,
-      DenseSet<OpOperand *> &usesWrite, const DominanceInfo &domInfo) const;
+  /// Return true if `value` has an ExtractSliceOp matching the given
+  /// InsertSliceOp in its reverse SSA use-def chain.
+  bool hasMatchingExtractSliceOp(Value value,
+                                 tensor::InsertSliceOp insertOp) const;
 
   /// Return true if bufferizing `opOperand` inplace with `opResult` would
   /// create a write to a non-writable buffer.
   bool wouldCreateWriteToNonWritableBuffer(OpOperand &opOperand,
                                            OpResult opResult) const;
 
   /// Assume that result bufferizes in-place with one of the operation's
-  /// operands. Return true if it is possible to find an inplace write W (resp.
-  /// a read R) among the uses of `aliasInfo[result]`, and a read R (resp. an
-  /// inplace write W) among the uses of
-  /// `aliasInfo[getAliasingOpOperand(result)]`, such that W and R interfere.
-  /// Interference detection is needed to determine which cases may bufferize
-  /// inplace without interferences. Such cases comprise:
-  ///
-  /// ```
-  ///  %0 = op_to_bufferize(%1)
-  ///  read(%1)
-  ///
-  ///  %0 = op_to_bufferize(%1)
-  ///  write(%0)
-  ///  read(%1)
-  ///
-  ///  %0 = op_to_bufferize(%1)
-  ///  write(%1)
-  ///  read(%0)
-  /// ```
+  /// operands. Return true if it is possible to find an inplace write W that
+  /// creates a conflict.
   bool
   wouldCreateReadAfterWriteInterference(OpOperand &operand, OpResult result,
                                         const DominanceInfo &domInfo) const;
@@ -171,54 +146,13 @@ class BufferizationAliasInfo {
   bool areEquivalentExtractSliceOps(tensor::ExtractSliceOp st,
                                     tensor::InsertSliceOp sti) const;
 
-  /// Return true if there is a `candidateOp` that would write to memory after
-  /// bufferization and such that:
-  ///   1. The written buffer is equivalent to either `aliasingRead` or
-  ///      `aliasingWrite` under the inPlace bufferization decisions taken
-  ///      so far.
-  ///   2. `aliasingWrite` properly dominates `candidateOp`.
-  ///   3. `candidateOp` properly dominates `aliasingReadOp`.
-  // TODO: richer clobbering analysis with container-containee relationship
-  // instead of equivalence.
-  bool existsInterleavedValueClobber(OpOperand &aliasingRead,
-                                     OpOperand &aliasingWrite,
+  /// Given sets of uses and writes, return true if there is a RaW conflict
+  /// under the assumption that all given reads/writes alias the same buffer and
+  /// that all given writes bufferize inplace.
+  bool hasReadAfterWriteInterference(const DenseSet<OpOperand *> &usesRead,
+                                     const DenseSet<OpOperand *> &usesWrite,
                                      const DominanceInfo &domInfo) const;
 
-  /// Return true if there is a write that:
-  ///   1. Properly dominates aliasingReadOp.
-  ///   2. Is properly dominated by aliasingWriteOp.
-  ///   3. Clobbers the write that would be interfering with the read.
-  ///
-  /// Case discussion:
-  /// ================
-  /// Case 1: opOperand is produced by opToBufferize,
-  /// Case 2: opResult is produced by opToBufferize,
-  /// Common case:
-  ///   - aliasingReadOp is a read to an alias of opOperand.
-  ///   - aliasingWriteOp is an inplace write to an alias of opResult.
-  ///   - aliasingWriteOp dominates aliasingReadOp.
-  ///
-  /// ```
-  ///    // Either case 1:
-  ///    %opOperand = opToBufferize(%opResult)
-  ///    aliasingWriteOp(%aliasingWrite = alias(%opResult)) // inplace
-  ///     aliasingReadOp( %aliasingRead = alias(%opOperand))
-  /// ```
-  ///
-  /// ```
-  ///    // Or case 2:
-  ///    %opResult = opToBufferize(%opOperand)
-  ///    aliasingWriteOp(%aliasingWrite = alias(%opResult)) // inplace
-  ///     aliasingReadOp( %aliasingRead = alias(%opOperand))
-  /// ```
-  ///
-  /// Capture possible cases where `aliasingWriteOp(alias(%opResult))` has no
-  /// visible effect on `aliasingReadOp(alias(%opOperand))`.
-  bool isClobberedWriteBeforeRead(Operation *opToBufferize,
-                                  OpOperand &aliasingRead,
-                                  OpOperand &aliasingWrite,
-                                  const DominanceInfo &domInfo) const;
-
   /// Set of tensors that are known to bufferize to writable memory.
   llvm::DenseSet<Value> bufferizeToWritableMemory;