[mlir][Vector] Move vector.mask canonicalization to folders

This MR moves the canonicalization that elides empty `vector.mask` ops
to folders.

Author: dcaballe

mlir/include/mlir/Dialect/Vector/IR/VectorOps.td

@@ -2554,7 +2554,7 @@ def Vector_MaskOp : Vector_Op<"mask", [
                                  Location loc);
   }];
 
-  let hasCanonicalizer = 1;
+  let hasCanonicalizer = 0;
   let hasFolder = 1;
   let hasCustomAssemblyFormat = 1;
   let hasVerifier = 1;

mlir/lib/Dialect/Vector/IR/VectorOps.cpp

@@ -6631,13 +6631,42 @@ LogicalResult MaskOp::verify() {
   return success();
 }
 
-/// Folds vector.mask ops with an all-true mask.
+/// Folds empty `vector.mask` with no passthru operand and with or without
+/// return values. For example:
+///
+///   %0 = vector.mask %mask { vector.yield %a : vector<8xf32> } :
+///     vector<8xi1> -> vector<8xf32>
+///   %1 = user_op %0 : vector<8xf32>
+///
+/// becomes:
+///
+///   %0 = user_op %a : vector<8xf32>
+///
+/// `vector.mask` with a passthru is handled by the canonicalizer.
+///
+static LogicalResult foldEmptyMaskOp(MaskOp maskOp, MaskOp::FoldAdaptor adaptor,
+                                     SmallVectorImpl<OpFoldResult> &results) {
+  if (!maskOp.isEmpty() || maskOp.hasPassthru())
+    return failure();
+
+  Block *block = maskOp.getMaskBlock();
+  auto terminator = cast<vector::YieldOp>(block->front());
+  if (terminator.getNumOperands() == 0) {
+    // `vector.mask` has no results, just remove the `vector.mask`.
+    return success();
+  }
+
+  // `vector.mask` has results, propagate the results.
+  llvm::append_range(results, terminator.getOperands());
+  return success();
+}
+
 LogicalResult MaskOp::fold(FoldAdaptor adaptor,
                            SmallVectorImpl<OpFoldResult> &results) {
-  MaskFormat maskFormat = getMaskFormat(getMask());
-  if (isEmpty())
-    return failure();
+  if (succeeded(foldEmptyMaskOp(*this, adaptor, results)))
+    return success();
 
+  MaskFormat maskFormat = getMaskFormat(getMask());
   if (maskFormat != MaskFormat::AllTrue)
     return failure();
 
@@ -6650,37 +6679,6 @@ LogicalResult MaskOp::fold(FoldAdaptor adaptor,
   return success();
 }
 
-// Elides empty vector.mask operations with or without return values. Propagates
-// the yielded values by the vector.yield terminator, if any, or erases the op,
-// otherwise.
-class ElideEmptyMaskOp : public OpRewritePattern<MaskOp> {
-  using OpRewritePattern::OpRewritePattern;
-
-  LogicalResult matchAndRewrite(MaskOp maskOp,
-                                PatternRewriter &rewriter) const override {
-    auto maskingOp = cast<MaskingOpInterface>(maskOp.getOperation());
-    if (maskingOp.getMaskableOp())
-      return failure();
-
-    if (!maskOp.isEmpty())
-      return failure();
-
-    Block *block = maskOp.getMaskBlock();
-    auto terminator = cast<vector::YieldOp>(block->front());
-    if (terminator.getNumOperands() == 0)
-      rewriter.eraseOp(maskOp);
-    else
-      rewriter.replaceOp(maskOp, terminator.getOperands());
-
-    return success();
-  }
-};
-
-void MaskOp::getCanonicalizationPatterns(RewritePatternSet &results,
-                                         MLIRContext *context) {
-  results.add<ElideEmptyMaskOp>(context);
-}
-
 // MaskingOpInterface definitions.
 
 /// Returns the operation masked by this 'vector.mask'.

mlir/test/Conversion/GPUCommon/lower-vector.mlir

@@ -1,10 +1,12 @@
 // RUN: mlir-opt %s --gpu-to-llvm | FileCheck %s
 
 module {
+  // CHECK-LABEL: func @func
+  // CHECK-SAME: %[[IN:.*]]: vector<11xf32>
   func.func @func(%arg: vector<11xf32>) -> vector<11xf32> {
     %cst_41 = arith.constant dense<true> : vector<11xi1>
-    // CHECK: vector.mask
-    // CHECK-SAME: vector.yield %arg0
+    // CHECK-NOT: vector.mask
+    // CHECK: return %[[IN]] : vector<11xf32>
     %127 = vector.mask %cst_41 { vector.yield %arg : vector<11xf32> } : vector<11xi1> -> vector<11xf32>
     return %127 : vector<11xf32>
   }