[llvm] 71eb8c0 - [AMDGPU] Update amdgpu_cs_chain_preserve docs. NFC

[Diana Picus via llvm-commits]

Author: Diana Picus
Date: 2023-08-24T10:17:00+02:00
New Revision: 71eb8c07dd9b57c5c4cc6981fae9323fadb7003d

URL: https://github.com/llvm/llvm-project/commit/71eb8c07dd9b57c5c4cc6981fae9323fadb7003d
DIFF: https://github.com/llvm/llvm-project/commit/71eb8c07dd9b57c5c4cc6981fae9323fadb7003d.diff

LOG: [AMDGPU] Update amdgpu_cs_chain_preserve docs. NFC

We no longer allow calls to functions with the `amdgpu_gfx` calling
convention from functions with the `amdgpu_cs_chain_preserve` calling
convention. See D153517.

Also mention that we can't have a chain call from
amdgpu_cs_chain_preserve using more VGPRs than it has received.

Differential Revision: https://reviews.llvm.org/D156408

Added: 
    

Modified: 
    llvm/docs/AMDGPUUsage.rst

Removed: 
    


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diff  --git a/llvm/docs/AMDGPUUsage.rst b/llvm/docs/AMDGPUUsage.rst
index c0290d10871e03..506d193d9806a0 100644
--- a/llvm/docs/AMDGPUUsage.rst
+++ b/llvm/docs/AMDGPUUsage.rst
@@ -1196,6 +1196,8 @@ The AMDGPU backend supports the following calling conventions:
                                      uniform control flow.
 
      ``amdgpu_cs_chain_preserve``    Same as ``amdgpu_cs_chain``, but active lanes for VGPRs starting at v8 are preserved.
+                                     Calls to ``amdgpu_gfx`` functions are not allowed, and any calls to ``llvm.amdgcn.cs.chain``
+                                     must not pass more VGPR arguments than the caller's VGPR function parameters.
 
      ``amdgpu_es``                   Used for AMDPAL shader stage before geometry shader if geometry is in
                                      use. So either the domain (= tessellation evaluation) shader if