Index: llvm/docs/AMDGPUUsage.rst
===================================================================
--- llvm/docs/AMDGPUUsage.rst
+++ llvm/docs/AMDGPUUsage.rst
@@ -999,7 +999,12 @@
      "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 IR implied default value is 1,1024. Clang may emit this attribute
+                                             with more restrictive bounds depending on language defaults.
+                                             If the actual block or workgroup size exceeds the limit at any point during
+                                             the execution, the behavior is undefined. For example, even if there is
+                                             only one active thread but the thread local id exceeds the limit, the
+                                             behavior is undefined.
 
      "amdgpu-implicitarg-num-bytes"="n"      Number of kernel argument bytes to add to the kernel
                                              argument block size for the implicit arguments. This