[mlir][affine] allow iter args as valid dims

that is effectivevely a revert of
7aabf47 for
mlir/lib/Dialect/Affine/IR/AffineOps.cpp

As iter args can be used as a dims is some
situations. For example in

[heir PolynomialToModArith](https://github.com/google/heir/blob/main/lib/Dialect/Polynomial/Conversions/PolynomialToModArith/PolynomialToModArith.cpp#L1036)

`rootExp`` and `batchSize`` are iter args that are
being used as dims and from the point of internal
loops they are fixed.

Author: metaflow

mlir/lib/Dialect/Affine/IR/AffineOps.cpp

@@ -294,12 +294,10 @@ bool mlir::affine::isValidDim(Value value) {
     return isValidDim(value, getAffineScope(defOp));
 
   // This value has to be a block argument for an op that has the
-  // `AffineScope` trait or an induction var of an affine.for or
-  // affine.parallel.
-  if (isAffineInductionVar(value))
-    return true;
+  // `AffineScope` trait or for an affine.for or affine.parallel.
   auto *parentOp = llvm::cast<BlockArgument>(value).getOwner()->getParentOp();
-  return parentOp && parentOp->hasTrait<OpTrait::AffineScope>();
+  return parentOp && (parentOp->hasTrait<OpTrait::AffineScope>() ||
+                      isa<AffineForOp, AffineParallelOp>(parentOp));
 }
 
 // Value can be used as a dimension id iff it meets one of the following
@@ -318,9 +316,10 @@ bool mlir::affine::isValidDim(Value value, Region *region) {
 
   auto *op = value.getDefiningOp();
   if (!op) {
-    // This value has to be an induction var for an affine.for or an
+    // This value has to be a block argument for an affine.for or an
     // affine.parallel.
-    return isAffineInductionVar(value);
+    auto *parentOp = llvm::cast<BlockArgument>(value).getOwner()->getParentOp();
+    return isa<AffineForOp, AffineParallelOp>(parentOp);
   }
 
   // Affine apply operation is ok if all of its operands are ok.