[mlir][quant] Fix quantization example. (#151518)

Fix and improve code example

[email protected]

Author: javedabsar1

mlir/include/mlir/Dialect/Quant/IR/QuantTypes.h

@@ -143,9 +143,11 @@ class QuantizedType : public Type {
   /// Casts from a type based on the storageType to a corresponding type based
   /// on this type (returns nullptr if the cast is not valid).
   /// Examples:
+  ///  `candidate type` -> `return type`
   ///   i8 -> !quant.uniform<i8:f32, 1.0>
   ///   tensor<4xi8> -> tensor<4x!quant.uniform<i8:f32, 1.0}>>
   ///   vector<4xi8> -> vector<4x!quant.uniform<i8:f32, 1.0>>
+  ///   It is assumed above that this type's quantization is `<i8:f32, 1.0>`.
   Type castFromStorageType(Type candidateType);
 
   /// Casts from a type based on a QuantizedType to a corresponding type based

mlir/lib/Dialect/Quant/IR/QuantTypes.cpp

@@ -127,7 +127,7 @@ QuantizedType::getQuantizedElementType(Type primitiveOrContainerType) {
 
 Type QuantizedType::castFromStorageType(Type candidateType) {
   if (candidateType == getStorageType()) {
-    // i.e. i32 -> quant<"uniform[i8:f32]{1.0}">
+    // i.e. i8 -> quant<"uniform[i8:f32]{1.0}">
     return *this;
   }
   if (llvm::isa<RankedTensorType>(candidateType)) {
@@ -137,11 +137,11 @@ Type QuantizedType::castFromStorageType(Type candidateType) {
         getStorageType());
   }
   if (llvm::isa<UnrankedTensorType>(candidateType)) {
-    // i.e. tensor<i8> -> tensor<!quant<"uniform[i8:f32]{1.0}">>
+    // i.e. tensor<xi8> -> tensor<x!quant<"uniform[i8:f32]{1.0}">>
     return UnrankedTensorType::get(getStorageType());
   }
   if (llvm::isa<VectorType>(candidateType)) {
-    // i.e. tensor<4xi8> -> tensor<4x!quant<"uniform[i8:f32]{1.0}">>
+    // i.e. vector<4xi8> -> vector<4x!quant<"uniform[i8:f32]{1.0}">>
     return VectorType::get(llvm::cast<VectorType>(candidateType).getShape(),
                            getStorageType());
   }