1 files changed, 34 insertions, 17 deletions
diff --git a/src/backends/aclCommon/ArmComputeTensorUtils.cpp b/src/backends/aclCommon/ArmComputeTensorUtils.cpp
index 517b11ced8..38c7f70da5 100644
--- a/src/backends/aclCommon/ArmComputeTensorUtils.cpp
+++ b/src/backends/aclCommon/ArmComputeTensorUtils.cpp
@@ -1,11 +1,12 @@
 //
-// Copyright © 2017 Arm Ltd and Contributors. All rights reserved.
+// Copyright © 2017,2022 Arm Ltd and Contributors. All rights reserved.
 // SPDX-License-Identifier: MIT
 //
 #include <aclCommon/ArmComputeTensorUtils.hpp>
 #include <aclCommon/ArmComputeUtils.hpp>
 
 #include "armnn/Exceptions.hpp"
+#include "ArmComputeUtils.hpp"
 #include <armnn/Descriptors.hpp>
 
 #include <fmt/format.h>
@@ -293,28 +294,44 @@ arm_compute::PermutationVector BuildArmComputePermutationVector(const armnn::Per
 
 arm_compute::PermutationVector BuildArmComputeTransposeVector(const armnn::PermutationVector& perm)
 {
-    arm_compute::PermutationVector aclPerm;
-    std::map<unsigned int, unsigned int> permuteMappings;
-    for (unsigned int i = 0; i < perm.GetSize(); ++i)
-    {
-        permuteMappings[perm[i]] = i;
-    }
+    // As ArmNN indexes are left to right and ACL indexes are right to left,
+    // the permutation vector has to be reversed and then translated into ACL axis.
+    // i.e. {1, 0, 2, 3} --> {3, 2, 0, 1} --> {0, 1, 3, 2}
+
+    // Below an example of how the ArmNN and ACL index format work:
+    // ArmNN Format:
+    // Input Shape        {1, 10, 20, 30}
+    // Permutation Vector {1,  0,  2,  3}
+    // Output Shape       {10, 1, 20, 30}
+    // dim "1" of input goes into index 0 of the output ([ 10, X, X, X])
+    // dim "0" of input goes into index 1 of the output ([ 10, 1, X, X ])
+    // dim "2" of input goes into index 2 of the output ([ 10, 1, 20, X ])
+    // dim "3" of input goes into index 3 of the output ([ 10, 1, 20, 30 ])
+    // ACL Format:
+    // Input Shape        {30, 20, 10, 1}
+    // Permutation Vector {0,  1,  3,  2}
+    // Output Shape       {30, 20, 1, 10}
+    // dim "0" of input goes into index 0 of the output ([ 30,  X, X, X])
+    // dim "1" of input goes into index 1 of the output ([ 30, 20, X, X ])
+    // dim "3" of input goes into index 2 of the output ([ 30, 20, 1, X ])
+    // dim "2" of input goes into index 3 of the output ([ 30, 20, 1, 10 ])
 
-    std::vector<unsigned int> permuteVector;
-    for (unsigned int i = 0; i < perm.GetSize(); ++i)
-    {
-        permuteVector.push_back(permuteMappings.at(i));
-    }
+    arm_compute::PermutationVector aclPerm;
+    auto rank = perm.GetSize();
 
-    unsigned int start = 0;
-    while ((start < perm.GetSize()) && (start == permuteVector[start]))
+    // Reverse the order. i.e. {1, 0, 2, 3} --> {3, 2, 0, 1}
+    std::vector<unsigned int> reversedPerm;
+    reversedPerm.reserve(rank);
+    for (unsigned int i = rank; i > 0; --i)
     {
-        ++start;
+        reversedPerm.push_back(perm[i-1]);
     }
 
-    for (unsigned int i = start; i < perm.GetSize(); ++i)
+    // Translate from Arm NN axis to ACL axis. i.e. {3, 2, 0, 1} --> {0, 1, 3, 2}
+    for (unsigned int i = 0; i < rank; ++i)
     {
-        aclPerm.set(i - start, permuteVector[i] - start);
+        auto aclAxis = rank - 1 - reversedPerm[i];
+        aclPerm.set(i, aclAxis);
     }
     return aclPerm;
 }