From e362095e451fba7783fff2ffe2df45f0c6e443ee Mon Sep 17 00:00:00 2001
From: hong <43953930+phlrain@users.noreply.github.com>
Date: Thu, 16 Jul 2020 10:43:11 +0800
Subject: [PATCH] fix softmax with cross entropy out of bound; test=develop
 (#25549)

---
 paddle/fluid/operators/softmax_with_cross_entropy_op.cu | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/paddle/fluid/operators/softmax_with_cross_entropy_op.cu b/paddle/fluid/operators/softmax_with_cross_entropy_op.cu
index 344dfe2399..ba56e5e36f 100644
--- a/paddle/fluid/operators/softmax_with_cross_entropy_op.cu
+++ b/paddle/fluid/operators/softmax_with_cross_entropy_op.cu
@@ -27,9 +27,11 @@ __global__ void CrossEntropyGrad(T* logit_grad, const int64_t* labels,
   CUDA_KERNEL_LOOP(index, n * remain) {
     int idx_n = index / remain;
     int idx_remain = index % remain;
-    int idx = idx_n * d + labels[index] * remain + idx_remain;
-    logit_grad[idx] -=
-        ignore_index == labels[index] ? static_cast<T>(0.) : static_cast<T>(1.);
+    int tmp = labels[index];
+    if (ignore_index != tmp) {
+      int idx = idx_n * d + tmp * remain + idx_remain;
+      logit_grad[idx] -= static_cast<T>(1.);
+    }
   }
 }
 
-- 
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