[llvm] [AMDGPU] Add note about inactive VGPR lanes being preserved (PR #185672)

[Jay Foad via llvm-commits]

https://github.com/jayfoad created https://github.com/llvm/llvm-project/pull/185672

None

>From e716da8440a6eeefadcbe6ae0957d2524111536b Mon Sep 17 00:00:00 2001
From: Jay Foad <jay.foad at amd.com>
Date: Tue, 10 Mar 2026 15:39:01 +0000
Subject: [PATCH] [AMDGPU] Add note about inactive VGPR lanes being preserved

---
 llvm/docs/AMDGPUUsage.rst | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/llvm/docs/AMDGPUUsage.rst b/llvm/docs/AMDGPUUsage.rst
index 036b4461ec06d..2e50f50b14177 100644
--- a/llvm/docs/AMDGPUUsage.rst
+++ b/llvm/docs/AMDGPUUsage.rst
@@ -2323,6 +2323,8 @@ callable functions (i.e. those that do not correspond to hardware entry points):
   are in an indeterminate state.
 * On return from a function, all dependency counters must be zero except for
   ``VScnt``/``STOREcnt``.
+* Inactive lanes of all VGPRs are preserved so they have the same value at
+  function exit as they did at the corresponding function entry.
 
 For entry points, the ABI conventions are dictated by the hardware behavior at
 wave launch and wave termination: