Index: llvm/docs/AMDGPUUsage.rst
===================================================================
--- llvm/docs/AMDGPUUsage.rst
+++ llvm/docs/AMDGPUUsage.rst
@@ -986,7 +986,10 @@
      "amdgpu-flat-work-group-size"="min,max" Specify the minimum and maximum flat work group sizes that
                                              will be specified when the kernel is dispatched. Generated
                                              by the ``amdgpu_flat_work_group_size`` CLANG attribute [CLANG-ATTR]_.
-                                             The implied default value is 1,1024.
+                                             The implied default value is 1,1024. The behavior is
+                                             undefined if the number of logically active lanes
+                                             exceeds the upper limit of this range at any point in
+                                             the execution.
 
      "amdgpu-implicitarg-num-bytes"="n"      Number of kernel argument bytes to add to the kernel
                                              argument block size for the implicit arguments. This