[webgpu] Use conv2dByMatMul by default when filter size is 1x1 (#2693)

PERF

Author: haoyunfeix

tfjs-backend-webgpu/src/backend_webgpu.ts

@@ -700,11 +700,6 @@ export class WebGPUBackend extends KernelBackend {
 
   conv2d(x: Tensor4D, filter: Tensor4D, convInfo: backend_util.Conv2DInfo):
       Tensor4D {
-    if (env().getBool('WEBGPU_CONV_SEPARATE_IM2COL_SHADER') &&
-        x.shape[0] === 1) {
-      return this.conv2dWithIm2Col(x, filter, convInfo);
-    }
-
     if (convInfo.filterHeight === 1 && convInfo.filterWidth === 1 &&
         convInfo.dilationHeight === 1 && convInfo.dilationWidth === 1 &&
         convInfo.strideHeight === 1 && convInfo.strideWidth === 1 &&
@@ -713,6 +708,11 @@ export class WebGPUBackend extends KernelBackend {
       return this.conv2dByMatMul(x, filter, convInfo);
     }
 
+    if (env().getBool('WEBGPU_CONV_SEPARATE_IM2COL_SHADER') &&
+        x.shape[0] === 1) {
+      return this.conv2dWithIm2Col(x, filter, convInfo);
+    }
+
     const dataId = this.write(null /*values*/, convInfo.outShape, x.dtype);
     const output =
         engine().makeTensorFromDataId(dataId, convInfo.outShape, x.dtype, this);