[amdgpu] Default to code object v3

[amdgpu] Default to code object v3
v4 is not yet readily available, and doesn't appear
to be implemented in the back end

Reviewed By: t-tye

Differential Revision: https://reviews.llvm.org/D93258

Author: JonChesterfield

clang/include/clang/Driver/Options.td

@@ -2811,7 +2811,7 @@ def mexec_model_EQ : Joined<["-"], "mexec-model=">, Group<m_wasm_Features_Driver
                      HelpText<"Execution model (WebAssembly only)">;
 
 def mcode_object_version_EQ : Joined<["-"], "mcode-object-version=">, Group<m_Group>,
-  HelpText<"Specify code object ABI version. Defaults to 4. (AMDGPU only)">,
+  HelpText<"Specify code object ABI version. Defaults to 3. (AMDGPU only)">,
   MetaVarName<"<version>">, Values<"2,3,4">;
 
 def mcode_object_v3_legacy : Flag<["-"], "mcode-object-v3">, Group<m_Group>,

clang/lib/Driver/ToolChains/CommonArgs.cpp

@@ -1549,7 +1549,7 @@ unsigned tools::getOrCheckAMDGPUCodeObjectVersion(
     const Driver &D, const llvm::opt::ArgList &Args, bool Diagnose) {
   const unsigned MinCodeObjVer = 2;
   const unsigned MaxCodeObjVer = 4;
-  unsigned CodeObjVer = 4;
+  unsigned CodeObjVer = 3;
 
   // Emit warnings for legacy options even if they are overridden.
   if (Diagnose) {

llvm/docs/AMDGPUUsage.rst

@@ -911,12 +911,12 @@ The AMDGPU backend uses the following ELF header:
 
   * ``ELFABIVERSION_AMDGPU_HSA_V3`` is used to specify the version of AMD HSA
     runtime ABI for code object V3. Specify using the Clang option
-    ``-mcode-object-version=3``.
+    ``-mcode-object-version=3``. This is the default code object
+    version if not specified.
 
   * ``ELFABIVERSION_AMDGPU_HSA_V4`` is used to specify the version of AMD HSA
     runtime ABI for code object V4. Specify using the Clang option
-    ``-mcode-object-version=4``. This is the default code object
-    version if not specified.
+    ``-mcode-object-version=4``.
 
   * ``ELFABIVERSION_AMDGPU_PAL`` is used to specify the version of AMD PAL
     runtime ABI.
@@ -2871,10 +2871,6 @@ non-AMD key names should be prefixed by "*vendor-name*.".
 Code Object V3 Metadata
 +++++++++++++++++++++++
 
-.. warning::
-  Code object V3 is not the default code object version emitted by this version
-  of LLVM.
-
 Code object V3 to V4 metadata is specified by the ``NT_AMDGPU_METADATA`` note
 record (see :ref:`amdgpu-note-records-v3-v4`).
 
@@ -3279,6 +3275,10 @@ same *vendor-name*.
 Code Object V4 Metadata
 +++++++++++++++++++++++
 
+.. warning::
+  Code object V4 is not the default code object version emitted by this version
+  of LLVM.
+
 Code object V4 metadata is the same as
 :ref:`amdgpu-amdhsa-code-object-metadata-v3` with the changes and additions
 defined in table :ref:`amdgpu-amdhsa-code-object-metadata-map-table-v3`.