fix pool with mask layer bug

paddle/math/Matrix.cpp

@@ -2157,26 +2157,20 @@ void CpuMatrix::maxPoolForward(Matrix& inputMat,
           int wend = wstart + sizeX;
           wstart = wstart < 0 ? 0 : wstart;
           wend = wend < (int)imgSizeW ? wend : (int)imgSizeW;
-          if (maskData == NULL) {
-            real tmp = -(real)FLT_MAX;
-            for (int h = hstart; h < hend; ++h) {
-              for (int w = wstart; w < wend; ++w) {
-                tmp = tmp < inputData[h * imgSizeW + w]
-                          ? inputData[h * imgSizeW + w]
-                          : tmp;
-              }
-            }
-            outData[ph * outputW + pw] = tmp;
-          } else {
+
+          real maxval = -(real)FLT_MAX;
+          int max_index = -1;
           for (int h = hstart; h < hend; ++h) {
             for (int w = wstart; w < wend; ++w) {
-                if (outData[ph * outputW + pw] < inputData[h * imgSizeW + w]) {
-                  outData[ph * outputW + pw] = inputData[h * imgSizeW + w];
-                  maskData[ph * outputW + pw] = h * imgSizeW + w;
-                }
+              if (maxval < inputData[h * imgSizeW + w]) {
+                maxval = inputData[h * imgSizeW + w];
+                max_index = h * imgSizeW + w;
               }
             }
           }
+
+          outData[ph * outputW + pw] = maxval;
+          if (maskData != NULL) maskData[ph * outputW + pw] = max_index;
         }
       }
       // compute offset