From 9bf7003902c9eacf5e2f1f7a5d039c08fd66cb0c Mon Sep 17 00:00:00 2001
From: hong <43953930+phlrain@users.noreply.github.com>
Date: Fri, 17 Jul 2020 17:18:31 +0800
Subject: [PATCH] fix softmax with cross entropy out of bound; test=develop
 (#25549) (#25567)

* fix softmax with cross entropy out of bound; test=develop (#25549)

* fix index error; test=develop
---
 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 dbda4b9b7e..80837bb3c3 100644
--- a/paddle/fluid/operators/softmax_with_cross_entropy_op.cu
+++ b/paddle/fluid/operators/softmax_with_cross_entropy_op.cu
@@ -28,9 +28,11 @@ __global__ void CrossEntropyGrad(T* logit_grad, const int64_t* labels,
        i += blockDim.x * gridDim.x) {
     int idx_n = i / remain;
     int idx_remain = i % remain;
-    int idx = idx_n * d + labels[i] * remain + idx_remain;
-    logit_grad[idx] -=
-        ignore_index == labels[i] ? static_cast<T>(0.) : static_cast<T>(1.);
+    int tmp = labels[i];
+    if (ignore_index != tmp) {
+      int idx = idx_n * d + tmp * remain + idx_remain;
+      logit_grad[idx] -= static_cast<T>(1.);
+    }
   }
 }
 
-- 
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