[mlir][Vector] Teach how to materialize UB constant to Vector (llvm#125596)

This PR adds support for UB constant materialization (i.e., generating
`ub::PoisonOp` to `VectorDialect::materializeConstant`. This was the
reason why the vector folders generating poison didn't work.

Author: dcaballe

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

@@ -437,6 +437,9 @@ void VectorDialect::initialize() {
 Operation *VectorDialect::materializeConstant(OpBuilder &builder,
                                               Attribute value, Type type,
                                               Location loc) {
+  if (isa<ub::PoisonAttrInterface>(value))
+    return value.getDialect().materializeConstant(builder, value, type, loc);
+
   return arith::ConstantOp::materialize(builder, value, type, loc);
 }
 
@@ -2273,20 +2276,6 @@ LogicalResult foldExtractFromFromElements(ExtractOp extractOp,
   return success();
 }
 
-/// Fold an insert or extract operation into an poison value when a poison index
-/// is found at any dimension of the static position.
-template <typename OpTy>
-LogicalResult
-canonicalizePoisonIndexInsertExtractOp(OpTy op, PatternRewriter &rewriter) {
-  if (auto poisonAttr = foldPoisonIndexInsertExtractOp(
-          op.getContext(), op.getStaticPosition(), OpTy::kPoisonIndex)) {
-    rewriter.replaceOpWithNewOp<ub::PoisonOp>(op, op.getType(), poisonAttr);
-    return success();
-  }
-
-  return failure();
-}
-
 } // namespace
 
 void ExtractOp::getCanonicalizationPatterns(RewritePatternSet &results,
@@ -2295,7 +2284,6 @@ void ExtractOp::getCanonicalizationPatterns(RewritePatternSet &results,
               ExtractOpFromBroadcast, ExtractOpFromCreateMask>(context);
   results.add(foldExtractFromShapeCastToShapeCast);
   results.add(foldExtractFromFromElements);
-  results.add(canonicalizePoisonIndexInsertExtractOp<ExtractOp>);
 }
 
 static void populateFromInt64AttrArray(ArrayAttr arrayAttr,
@@ -3068,7 +3056,6 @@ void InsertOp::getCanonicalizationPatterns(RewritePatternSet &results,
                                            MLIRContext *context) {
   results.add<InsertToBroadcast, BroadcastFolder, InsertSplatToSplat,
               InsertOpConstantFolder>(context);
-  results.add(canonicalizePoisonIndexInsertExtractOp<InsertOp>);
 }
 
 OpFoldResult vector::InsertOp::fold(FoldAdaptor adaptor) {

mlir/test/Conversion/VectorToLLVM/vector-to-llvm.mlir

@@ -1250,13 +1250,13 @@ func.func @extract_scalar_from_vec_1d_f32(%arg0: vector<16xf32>) -> f32 {
 
 // -----
 
-func.func @extract_poison_idx(%arg0: vector<16xf32>) -> f32 {
+func.func @extract_scalar_from_vec_1d_f32_poison_idx(%arg0: vector<16xf32>) -> f32 {
   %0 = vector.extract %arg0[-1]: f32 from vector<16xf32>
   return %0 : f32
 }
-// CHECK-LABEL: @extract_poison_idx
-//       CHECK:   %[[IDX:.*]] = llvm.mlir.constant(-1 : i64) : i64
-//       CHECK:   llvm.extractelement {{.*}}[%[[IDX]] : i64] : vector<16xf32>
+// CHECK-LABEL: @extract_scalar_from_vec_1d_f32_poison_idx
+//       CHECK:   %[[UB:.*]] = ub.poison : f32
+//       CHECK:   return %[[UB]] : f32
 
 // -----
 
@@ -1335,6 +1335,16 @@ func.func @extract_vec_2d_from_vec_3d_f32(%arg0: vector<4x3x16xf32>) -> vector<3
 
 // -----
 
+func.func @extract_vec_2d_from_vec_3d_f32_poison_idx(%arg0: vector<4x3x16xf32>) -> vector<3x16xf32> {
+  %0 = vector.extract %arg0[-1]: vector<3x16xf32> from vector<4x3x16xf32>
+  return %0 : vector<3x16xf32>
+}
+// CHECK-LABEL: @extract_vec_2d_from_vec_3d_f32_poison_idx
+//       CHECK:   %[[UB:.*]] = ub.poison : vector<3x16xf32>
+//       CHECK:   return %[[UB]] : vector<3x16xf32>
+
+// -----
+
 func.func @extract_vec_2d_from_vec_3d_f32_scalable(%arg0: vector<4x3x[16]xf32>) -> vector<3x[16]xf32> {
   %0 = vector.extract %arg0[0]: vector<3x[16]xf32> from vector<4x3x[16]xf32>
   return %0 : vector<3x[16]xf32>