[WebGPU EP] Reduce duplicated code in MatMulReadFnSource() (#27151)

### Description
Previously in `MatMulReadFnSource()` we use duplicated code to read data
from two inputs `a` and `b`. This patch implements another overload of
`MatMulReadFnSource()` to only read data from one input to reduce
duplicated code and get ready for further use.

Author: Jiawei-Shao

onnxruntime/core/providers/webgpu/math/gemm_utils.cc

@@ -123,68 +123,56 @@ void InitializeLogicalWorkgroupIDAndGlobalID(ShaderHelper& shader) {
 }  // namespace
 
 void MatMulReadFnSource(ShaderHelper& shader,
-                        const ShaderVariableHelper& a,
-                        const ShaderVariableHelper& b,
+                        std::string_view function_name,
+                        const ShaderVariableHelper& input,
+                        const std::string& input_name,
                         const ShaderIndicesHelper* batch_dims,
-                        bool transA,
-                        bool transB) {
-  const int a_components = a.NumComponents();
+                        std::string_view rows,
+                        std::string_view components_per_row,
+                        bool transpose) {
+  const int components = input.NumComponents();
   const std::string data_type = "output_element_t";
-  std::string type_string = MakeScalarOrVectorType(a_components, data_type);
+  const std::string type_string = MakeScalarOrVectorType(components, data_type);
 
   shader.AdditionalImplementation()
-      << "fn mm_readA(batch: i32, row: i32, colIn: i32 "
+      << "fn " << function_name << "(batch: i32, row: i32, colIn: i32 "
       << (batch_dims
               ? ", batch_indices: batch_dims_indices_t"
               : "")
-      << ") -> " << type_string << " {\n"
-      << "  var value = " << type_string << "(0);\n"
-      << "  let col = colIn * " << a_components << ";\n";
-  if (transA) {
-    shader.AdditionalImplementation() << "  if(row < i32(uniforms.dim_inner) && col < i32(uniforms.dim_a_outer)) {\n";
+      << ") -> " << type_string << " {\n "
+      << "    var value = " << type_string << "(0);\n"
+      << "    let col = colIn * " << components << ";\n";
+  if (transpose) {
+    shader.AdditionalImplementation() << "    if(row < i32(" << components_per_row << ") && col < i32(" << rows << ")) {\n";
   } else {
-    shader.AdditionalImplementation() << "  if(row < i32(uniforms.dim_a_outer) && col < i32(uniforms.dim_inner)) {\n";
+    shader.AdditionalImplementation() << "    if(row < i32(" << rows << ") && col < i32(" << components_per_row << ")) {\n";
   }
-  shader.AdditionalImplementation() << "    var a_indices: a_indices_t;\n";
 
-  if (batch_dims) {
-    shader.AdditionalImplementation() << ConvertOutputBatchIndicesToInputBatchIndices("a", a, a.Rank() - 2, batch_dims ? batch_dims->Rank() : 0, " batch_indices ");
-  }
-  shader.AdditionalImplementation() << "    " << a.IndicesSet("a_indices", a.Rank() - 2, "u32(row)") << "\n"
-                                    << "    " << a.IndicesSet("a_indices", a.Rank() - 1, "u32(colIn)") << "\n"
-                                    << "    value = " << a.GetByIndices("a_indices") << ";\n"
-                                    << "  }\n"
-                                    << "  return value;\n"
-                                    << "}\n\n";
-
-  // Add the mm_readB function
-  const int b_components = b.NumComponents();
-  type_string = MakeScalarOrVectorType(b_components, data_type);
-  shader.AdditionalImplementation()
-      << "fn mm_readB(batch: i32, row: i32, colIn: i32 "
-      << (batch_dims
-              ? ", batch_indices: batch_dims_indices_t"
-              : "")
-      << ") -> " << type_string << " {\n"
-      << "  var value = " << type_string << "(0);\n"
-      << "  let col = colIn * " << b_components << ";\n";
+  const std::string input_indices = input_name + "_indices";
+  shader.AdditionalImplementation() << "        var " << input_indices << ": " << input_name << "_indices_t" << ";\n";
 
-  if (transB) {
-    shader.AdditionalImplementation() << "  if(row < i32(uniforms.dim_b_outer) && col < i32(uniforms.dim_inner)) {\n";
-  } else {
-    shader.AdditionalImplementation() << "  if(row < i32(uniforms.dim_inner) && col < i32(uniforms.dim_b_outer)) {\n";
+  if (batch_dims) {
+    shader.AdditionalImplementation() << ConvertOutputBatchIndicesToInputBatchIndices(input_name, input, input.Rank() - 2, batch_dims ? batch_dims->Rank() : 0, " batch_indices ") << "\n";
   }
 
-  shader.AdditionalImplementation() << "    var b_indices: b_indices_t;\n"
-                                    << ConvertOutputBatchIndicesToInputBatchIndices("b", b, b.Rank() - 2, batch_dims ? batch_dims->Rank() : 0, "batch_indices")
-                                    << "    " << b.IndicesSet("b_indices", b.Rank() - 2, "u32(row)") << "\n"
-                                    << "    " << b.IndicesSet("b_indices", b.Rank() - 1, "u32(colIn)") << "\n"
-                                    << "    value = " << b.GetByIndices("b_indices") << ";\n"
-                                    << "  }\n"
-                                    << "  return value;\n"
+  shader.AdditionalImplementation() << input.IndicesSet(input_indices, input.Rank() - 2, "u32(row)") << "\n"
+                                    << input.IndicesSet(input_indices, input.Rank() - 1, "u32(colIn)") << "\n"
+                                    << "        value = " << input.GetByIndices(input_indices) << ";\n"
+                                    << "    }\n"
+                                    << "    return value;\n"
                                     << "}\n\n";
 }
 
+void MatMulReadFnSource(ShaderHelper& shader,
+                        const ShaderVariableHelper& a,
+                        const ShaderVariableHelper& b,
+                        const ShaderIndicesHelper* batch_dims,
+                        bool transA,
+                        bool transB) {
+  MatMulReadFnSource(shader, "mm_readA", a, "a", batch_dims, "uniforms.dim_a_outer", "uniforms.dim_inner", transA);
+  MatMulReadFnSource(shader, "mm_readB", b, "b", batch_dims, "uniforms.dim_inner", "uniforms.dim_b_outer", transB);
+}
+
 void MatMulWriteFnSource(ShaderHelper& shader,
                          const ShaderVariableHelper& output,
                          const ShaderVariableHelper* bias,