[mlir][vector] Update helpers in VectorEmulateNarrowType.cpp (nfc) (llvm#131527)

Refactors the following pairs of helper hooks:
  * `dynamicallyInsertSubVector` + `staticallyInsertSubVector`
  * `dynamicallyExtractSubVector` + `staticallyExtractSubVector`

These hooks are very similar, so I have unified the variable names and
various conditions to make the actual differences clearer.

Author: banach-space

mlir/lib/Dialect/Vector/Transforms/VectorEmulateNarrowType.cpp

@@ -198,85 +198,156 @@ static FailureOr<Operation *> getCompressedMaskOp(OpBuilder &rewriter,
   return *newMask;
 }
 
-/// Extracts 1-D subvector from a 1-D vector. It is a wrapper function for
-/// emitting `vector.extract_strided_slice`.
+/// Extracts 1-D subvector from a 1-D vector.
+///
+/// Given the input rank-1 source vector, extracts `numElemsToExtract` elements
+/// from `src`, starting at `offset`. The result is also a rank-1 vector:
+///
+///   vector<numElemsToExtract x !elemType>
+///
+/// (`!elType` is the element type of the source vector). As `offset` is a known
+/// _static_ value, this helper hook emits `vector.extract_strided_slice`.
+///
+/// EXAMPLE:
+///     %res = vector.extract_strided_slice %src
+///       { offsets = [offset], sizes = [numElemsToExtract], strides = [1] }
 static Value staticallyExtractSubvector(OpBuilder &rewriter, Location loc,
-                                        Value source, int64_t frontOffset,
-                                        int64_t subvecSize) {
-  auto vectorType = cast<VectorType>(source.getType());
-  assert(vectorType.getRank() == 1 && "expected 1-D source types");
-  assert(frontOffset + subvecSize <= vectorType.getNumElements() &&
+                                        Value src, int64_t offset,
+                                        int64_t numElemsToExtract) {
+  auto vectorType = cast<VectorType>(src.getType());
+  assert(vectorType.getRank() == 1 && "expected source to be rank-1-D vector ");
+  assert(offset + numElemsToExtract <= vectorType.getNumElements() &&
          "subvector out of bounds");
 
-  // do not need extraction if the subvector size is the same as the source
-  if (vectorType.getNumElements() == subvecSize)
-    return source;
+  // When extracting all available elements, just use the source vector as the
+  // result.
+  if (vectorType.getNumElements() == numElemsToExtract)
+    return src;
 
-  auto offsets = rewriter.getI64ArrayAttr({frontOffset});
-  auto sizes = rewriter.getI64ArrayAttr({subvecSize});
+  auto offsets = rewriter.getI64ArrayAttr({offset});
+  auto sizes = rewriter.getI64ArrayAttr({numElemsToExtract});
   auto strides = rewriter.getI64ArrayAttr({1});
 
   auto resultVectorType =
-      VectorType::get({subvecSize}, vectorType.getElementType());
+      VectorType::get({numElemsToExtract}, vectorType.getElementType());
   return rewriter
-      .create<vector::ExtractStridedSliceOp>(loc, resultVectorType, source,
+      .create<vector::ExtractStridedSliceOp>(loc, resultVectorType, src,
                                              offsets, sizes, strides)
       ->getResult(0);
 }
 
-/// Inserts 1-D subvector into a 1-D vector by overwriting the elements starting
-/// at `offset`. it is a wrapper function for emitting
+/// Inserts 1-D subvector into a 1-D vector.
+///
+/// Inserts the input rank-1 source vector into the destination vector starting
+/// at `offset`. As `offset` is a known _static_ value, this helper hook emits
 /// `vector.insert_strided_slice`.
+///
+/// EXAMPLE:
+///   %res = vector.insert_strided_slice %src, %dest
+///     {offsets = [%offset], strides [1]}
 static Value staticallyInsertSubvector(OpBuilder &rewriter, Location loc,
                                        Value src, Value dest, int64_t offset) {
-  [[maybe_unused]] auto srcType = cast<VectorType>(src.getType());
-  [[maybe_unused]] auto destType = cast<VectorType>(dest.getType());
-  assert(srcType.getRank() == 1 && destType.getRank() == 1 &&
-         "expected source and dest to be vector type");
+  auto srcVecTy = cast<VectorType>(src.getType());
+  auto destVecTy = cast<VectorType>(dest.getType());
+  assert(srcVecTy.getRank() == 1 && destVecTy.getRank() == 1 &&
+         "expected source and dest to be rank-1 vector types");
+
+  // If overwritting the destination vector, just return the source.
+  if (srcVecTy.getNumElements() == destVecTy.getNumElements() && offset == 0)
+    return src;
+
   auto offsets = rewriter.getI64ArrayAttr({offset});
   auto strides = rewriter.getI64ArrayAttr({1});
-  return rewriter.create<vector::InsertStridedSliceOp>(loc, dest.getType(), src,
+  return rewriter.create<vector::InsertStridedSliceOp>(loc, destVecTy, src,
                                                        dest, offsets, strides);
 }
 
-/// Extracts a 1-D subvector from a 1-D `source` vector, with index at `offset`
-/// and size `numElementsToExtract`, and inserts into the `dest` vector. This
-/// function emits multiple `vector.extract` and `vector.insert` ops, so only
-/// use it when `offset` cannot be folded into a constant value.
+/// Extracts 1-D subvector from a 1-D vector.
+///
+/// Given the input rank-1 source vector, extracts `numElemsToExtact` elements
+/// from `src`, starting at `offset`. The result is also a rank-1 vector:
+///
+///   vector<numElemsToExtact x !elType>
+///
+/// (`!elType` is the element type of the source vector). As `offset` is assumed
+/// to be a _dynamic_ SSA value, this helper method generates a sequence of
+/// `vector.extract` + `vector.insert` pairs.
+///
+/// EXAMPLE:
+///     %v1 = vector.extract %src[%offset] : i2 from vector<8xi2>
+///     %r1 = vector.insert %v1, %dest[0] : i2 into vector<3xi2>
+///     %c1 = arith.constant 1 : index
+///     %idx2 = arith.addi %offset, %c1 : index
+///     %v2 = vector.extract %src[%idx2] : i2 from vector<8xi2>
+///     %r2 = vector.insert %v2, %r1 [1] : i2 into vector<3xi2>
+///     (...)
 static Value dynamicallyExtractSubVector(OpBuilder &rewriter, Location loc,
-                                         Value source, Value dest,
+                                         Value src, Value dest,
                                          OpFoldResult offset,
-                                         int64_t numElementsToExtract) {
-  assert(isa<VectorValue>(source) && "expected `source` to be a vector type");
-  for (int i = 0; i < numElementsToExtract; ++i) {
+                                         int64_t numElemsToExtract) {
+  auto srcVecTy = cast<VectorType>(src.getType());
+  assert(srcVecTy.getRank() == 1 && "expected source to be rank-1-D vector ");
+  // NOTE: We are unable to take the offset into account in the following
+  // assert, hence its still possible that the subvector is out-of-bounds even
+  // if the condition is true.
+  assert(numElemsToExtract <= srcVecTy.getNumElements() &&
+         "subvector out of bounds");
+
+  // When extracting all available elements, just use the source vector as the
+  // result.
+  if (srcVecTy.getNumElements() == numElemsToExtract)
+    return src;
+
+  for (int i = 0; i < numElemsToExtract; ++i) {
     Value extractLoc =
         (i == 0) ? offset.dyn_cast<Value>()
                  : rewriter.create<arith::AddIOp>(
                        loc, rewriter.getIndexType(), offset.dyn_cast<Value>(),
                        rewriter.create<arith::ConstantIndexOp>(loc, i));
-    auto extractOp =
-        rewriter.create<vector::ExtractOp>(loc, source, extractLoc);
+    auto extractOp = rewriter.create<vector::ExtractOp>(loc, src, extractLoc);
     dest = rewriter.create<vector::InsertOp>(loc, extractOp, dest, i);
   }
   return dest;
 }
 
-/// Inserts a 1-D subvector into a 1-D `dest` vector at index `destOffsetVar`.
+/// Inserts 1-D subvector into a 1-D vector.
+///
+/// Inserts the input rank-1 source vector into the destination vector starting
+/// at `offset`. As `offset` is assumed to be a _dynamic_ SSA value, this hook
+/// uses a sequence of `vector.extract` + `vector.insert` pairs.
+///
+/// EXAMPLE:
+///     %v1 = vector.extract %src[0] : i2 from vector<8xi2>
+///     %r1 = vector.insert %v1, %dest[%offset] : i2 into vector<3xi2>
+///     %c1 = arith.constant 1 : index
+///     %idx2 = arith.addi %offset, %c1 : index
+///     %v2 = vector.extract %src[1] : i2 from vector<8xi2>
+///     %r2 = vector.insert %v2, %r1 [%idx2] : i2 into vector<3xi2>
+///     (...)
 static Value dynamicallyInsertSubVector(RewriterBase &rewriter, Location loc,
-                                        Value source, Value dest,
-                                        OpFoldResult destOffsetVar,
-                                        size_t length) {
-  assert(isa<VectorValue>(source) && "expected `source` to be a vector type");
-  assert(length > 0 && "length must be greater than 0");
-  Value destOffsetVal =
-      getValueOrCreateConstantIndexOp(rewriter, loc, destOffsetVar);
-  for (size_t i = 0; i < length; ++i) {
+                                        Value src, Value dest,
+                                        OpFoldResult offset,
+                                        int64_t numElemsToInsert) {
+  auto srcVecTy = cast<VectorType>(src.getType());
+  auto destVecTy = cast<VectorType>(dest.getType());
+  assert(srcVecTy.getRank() == 1 && destVecTy.getRank() == 1 &&
+         "expected source and dest to be rank-1 vector types");
+  assert(numElemsToInsert > 0 &&
+         "the number of elements to insert must be greater than 0");
+  // NOTE: We are unable to take the offset into account in the following
+  // assert, hence its still possible that the subvector is out-of-bounds even
+  // if the condition is true.
+  assert(numElemsToInsert <= destVecTy.getNumElements() &&
+         "subvector out of bounds");
+
+  Value destOffsetVal = getValueOrCreateConstantIndexOp(rewriter, loc, offset);
+  for (int64_t i = 0; i < numElemsToInsert; ++i) {
     auto insertLoc = i == 0
                          ? destOffsetVal
                          : rewriter.create<arith::AddIOp>(
                                loc, rewriter.getIndexType(), destOffsetVal,
                                rewriter.create<arith::ConstantIndexOp>(loc, i));
-    auto extractOp = rewriter.create<vector::ExtractOp>(loc, source, i);
+    auto extractOp = rewriter.create<vector::ExtractOp>(loc, src, i);
     dest = rewriter.create<vector::InsertOp>(loc, extractOp, dest, insertLoc);
   }
   return dest;