Add syntactic sugar for strided memref parsing.

This CL implements the last remaining bit of the [strided memref proposal](https://groups.google.com/a/tensorflow.org/forum/#!topic/mlir/MaL8m2nXuio).

The syntax is a bit more explicit than what was originally proposed and resembles:
  `memref<?x?xf32, offset: 0 strides: [?, 1]>`

Nonnegative strides and offsets are currently supported. Future extensions will include negative strides.

This also gives a concrete example of syntactic sugar for the ([RFC] Proposed Changes to MemRef and Tensor MLIR Types)[https://groups.google.com/a/tensorflow.org/forum/#!topic/mlir/-wKHANzDNTg].

The underlying implementation still uses AffineMap layout.

PiperOrigin-RevId: 272717437

third_party/mlir/lib/IR/StandardTypes.cpp

@@ -492,7 +492,13 @@ static void extractStrides(AffineExpr e, MutableArrayRef<int64_t> strides,
     return;
   }
   if (bin.getKind() == AffineExprKind::Mul) {
-    auto dim = bin.getLHS().cast<AffineDimExpr>();
+    // LHS may be more complex than just a single dim (e.g. multiple syms and
+    // dims). Bail out for now and revisit when we have evidence this is needed.
+    auto dim = bin.getLHS().dyn_cast<AffineDimExpr>();
+    if (!dim) {
+      failed = true;
+      return;
+    }
     auto cst = bin.getRHS().dyn_cast<AffineConstantExpr>();
     if (!cst) {
       strides[dim.getPosition()] = MemRefType::kDynamicStrideOrOffset;

third_party/mlir/lib/Parser/Parser.cpp

@@ -38,7 +38,6 @@
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/StringSet.h"
 #include "llvm/ADT/bit.h"
-#include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/PrettyStackTrace.h"
 #include "llvm/Support/SMLoc.h"
 #include "llvm/Support/SourceMgr.h"
@@ -211,6 +210,14 @@ public:
                                        bool allowDynamic = true);
   ParseResult parseXInDimensionList();
 
+  /// Parse strided layout specification.
+  ParseResult parseStridedLayout(int64_t &offset,
+                                 SmallVectorImpl<int64_t> &strides);
+
+  // Parse a brace-delimiter list of comma-separated integers with `?` as an
+  // unknown marker.
+  ParseResult parseStrideList(SmallVectorImpl<int64_t> &dimensions);
+
   //===--------------------------------------------------------------------===//
   // Attribute Parsing
   //===--------------------------------------------------------------------===//
@@ -634,6 +641,40 @@ Type Parser::parseFunctionType() {
   return builder.getFunctionType(arguments, results);
 }
 
+/// Parse the offset and strides from a strided layout specification.
+///
+///   strided-layout ::= `offset:` dimension `,` `strides: ` stride-list
+///
+ParseResult Parser::parseStridedLayout(int64_t &offset,
+                                       SmallVectorImpl<int64_t> &strides) {
+  // Parse offset.
+  consumeToken(Token::kw_offset);
+  if (!consumeIf(Token::colon))
+    return emitError("expected colon after `offset` keyword");
+  auto maybeOffset = getToken().getUnsignedIntegerValue();
+  bool question = getToken().is(Token::question);
+  if (!maybeOffset && !question)
+    return emitError("invalid offset");
+  offset = maybeOffset ? static_cast<int64_t>(maybeOffset.getValue())
+                       : MemRefType::kDynamicStrideOrOffset;
+  consumeToken();
+
+  if (!consumeIf(Token::comma))
+    return emitError("expected comma after offset value");
+
+  // Parse stride list.
+  if (!consumeIf(Token::kw_strides))
+    return emitError("expected `strides` keyword after offset specification");
+  if (!consumeIf(Token::colon))
+    return emitError("expected colon after `strides` keyword");
+  if (failed(parseStrideList(strides)))
+    return emitError("invalid braces-enclosed stride list");
+  if (llvm::any_of(strides, [](int64_t st) { return st == 0; }))
+    return emitError("invalid memref stride");
+
+  return success();
+}
+
 /// Parse a memref type.
 ///
 ///   memref-type ::= `memref` `<` dimension-list-ranked type
@@ -675,18 +716,28 @@ Type Parser::parseMemRefType() {
       consumeToken(Token::integer);
       parsedMemorySpace = true;
     } else {
-      // Parse affine map.
       if (parsedMemorySpace)
-        return emitError("affine map after memory space in memref type");
-      auto affineMap = parseAttribute();
-      if (!affineMap)
-        return failure();
-
-      // Verify that the parsed attribute is an affine map.
-      if (auto affineMapAttr = affineMap.dyn_cast<AffineMapAttr>())
-        affineMapComposition.push_back(affineMapAttr.getValue());
-      else
-        return emitError("expected affine map in memref type");
+        return emitError("expected memory space to be last in memref type");
+      if (getToken().is(Token::kw_offset)) {
+        int64_t offset;
+        SmallVector<int64_t, 4> strides;
+        if (failed(parseStridedLayout(offset, strides)))
+          return failure();
+        // Construct strided affine map.
+        auto map = makeStridedLinearLayoutMap(strides, offset,
+                                              elementType.getContext());
+        affineMapComposition.push_back(map);
+      } else {
+        // Parse affine map.
+        auto affineMap = parseAttribute();
+        if (!affineMap)
+          return failure();
+        // Verify that the parsed attribute is an affine map.
+        if (auto affineMapAttr = affineMap.dyn_cast<AffineMapAttr>())
+          affineMapComposition.push_back(affineMapAttr.getValue());
+        else
+          return emitError("expected affine map in memref type");
+      }
     }
     return success();
   };
@@ -935,6 +986,38 @@ ParseResult Parser::parseXInDimensionList() {
   return success();
 }
 
+// Parse a comma-separated list of dimensions, possibly empty:
+//   stride-list ::= `[` (dimension (`,` dimension)*)? `]`
+ParseResult Parser::parseStrideList(SmallVectorImpl<int64_t> &dimensions) {
+  if (!consumeIf(Token::l_square))
+    return failure();
+  // Empty list early exit.
+  if (consumeIf(Token::r_square))
+    return success();
+  while (true) {
+    if (consumeIf(Token::question)) {
+      dimensions.push_back(MemRefType::kDynamicStrideOrOffset);
+    } else {
+      // This must be an integer value.
+      int64_t val;
+      if (getToken().getSpelling().getAsInteger(10, val))
+        return emitError("invalid integer value: ") << getToken().getSpelling();
+      // Make sure it is not the one value for `?`.
+      if (ShapedType::isDynamic(val))
+        return emitError("invalid integer value: ")
+               << getToken().getSpelling()
+               << ", use `?` to specify a dynamic dimension";
+      dimensions.push_back(val);
+      consumeToken(Token::integer);
+    }
+    if (!consumeIf(Token::comma))
+      break;
+  }
+  if (!consumeIf(Token::r_square))
+    return failure();
+  return success();
+}
+
 //===----------------------------------------------------------------------===//
 // Attribute parsing.
 //===----------------------------------------------------------------------===//

third_party/mlir/lib/Parser/TokenKinds.def

@@ -110,10 +110,12 @@ TOK_KEYWORD(memref)
 TOK_KEYWORD(min)
 TOK_KEYWORD(mod)
 TOK_KEYWORD(none)
+TOK_KEYWORD(offset)
 TOK_KEYWORD(opaque)
 TOK_KEYWORD(size)
 TOK_KEYWORD(sparse)
 TOK_KEYWORD(step)
+TOK_KEYWORD(strides)
 TOK_KEYWORD(symbol)
 TOK_KEYWORD(tensor)
 TOK_KEYWORD(to)