AMDHSA: Put old assembler docs back

Until we switch to code object v3 by default.
Follow up for https://reviews.llvm.org/D47736.

Differential Revision: https://reviews.llvm.org/D48497

llvm-svn: 335378

docs/AMDGPUUsage.rst

@@ -4303,8 +4303,103 @@ VOP_SDWA examples:
 
 For full list of supported instructions, refer to "Vector ALU instructions".
 
-Predefined Symbols
-~~~~~~~~~~~~~~~~~~
+.. TODO
+   Remove once we switch to code object v3 by default.
+
+HSA Code Object Directives
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+AMDGPU ABI defines auxiliary data in output code object. In assembly source,
+one can specify them with assembler directives.
+
+.hsa_code_object_version major, minor
++++++++++++++++++++++++++++++++++++++
+
+*major* and *minor* are integers that specify the version of the HSA code
+object that will be generated by the assembler.
+
+.hsa_code_object_isa [major, minor, stepping, vendor, arch]
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+
+*major*, *minor*, and *stepping* are all integers that describe the instruction
+set architecture (ISA) version of the assembly program.
+
+*vendor* and *arch* are quoted strings.  *vendor* should always be equal to
+"AMD" and *arch* should always be equal to "AMDGPU".
+
+By default, the assembler will derive the ISA version, *vendor*, and *arch*
+from the value of the -mcpu option that is passed to the assembler.
+
+.amdgpu_hsa_kernel (name)
++++++++++++++++++++++++++
+
+This directives specifies that the symbol with given name is a kernel entry point
+(label) and the object should contain corresponding symbol of type STT_AMDGPU_HSA_KERNEL.
+
+.amd_kernel_code_t
+++++++++++++++++++
+
+This directive marks the beginning of a list of key / value pairs that are used
+to specify the amd_kernel_code_t object that will be emitted by the assembler.
+The list must be terminated by the *.end_amd_kernel_code_t* directive.  For
+any amd_kernel_code_t values that are unspecified a default value will be
+used.  The default value for all keys is 0, with the following exceptions:
+
+- *kernel_code_version_major* defaults to 1.
+- *machine_kind* defaults to 1.
+- *machine_version_major*, *machine_version_minor*, and
+  *machine_version_stepping* are derived from the value of the -mcpu option
+  that is passed to the assembler.
+- *kernel_code_entry_byte_offset* defaults to 256.
+- *wavefront_size* defaults to 6.
+- *kernarg_segment_alignment*, *group_segment_alignment*, and
+  *private_segment_alignment* default to 4. Note that alignments are specified
+  as a power of two, so a value of **n** means an alignment of 2^ **n**.
+
+The *.amd_kernel_code_t* directive must be placed immediately after the
+function label and before any instructions.
+
+For a full list of amd_kernel_code_t keys, refer to AMDGPU ABI document,
+comments in lib/Target/AMDGPU/AmdKernelCodeT.h and test/CodeGen/AMDGPU/hsa.s.
+
+Here is an example of a minimal amd_kernel_code_t specification:
+
+.. code-block:: none
+
+   .hsa_code_object_version 1,0
+   .hsa_code_object_isa
+
+   .hsatext
+   .globl  hello_world
+   .p2align 8
+   .amdgpu_hsa_kernel hello_world
+
+   hello_world:
+
+      .amd_kernel_code_t
+         enable_sgpr_kernarg_segment_ptr = 1
+         is_ptr64 = 1
+         compute_pgm_rsrc1_vgprs = 0
+         compute_pgm_rsrc1_sgprs = 0
+         compute_pgm_rsrc2_user_sgpr = 2
+         kernarg_segment_byte_size = 8
+         wavefront_sgpr_count = 2
+         workitem_vgpr_count = 3
+     .end_amd_kernel_code_t
+
+     s_load_dwordx2 s[0:1], s[0:1] 0x0
+     v_mov_b32 v0, 3.14159
+     s_waitcnt lgkmcnt(0)
+     v_mov_b32 v1, s0
+     v_mov_b32 v2, s1
+     flat_store_dword v[1:2], v0
+     s_endpgm
+   .Lfunc_end0:
+        .size   hello_world, .Lfunc_end0-hello_world
+
+Predefined Symbols (-mattr=+code-object-v3)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 The AMDGPU assembler defines and updates some symbols automatically. These
 symbols do not affect code generation.
@@ -4343,8 +4438,8 @@ May be used to set the `.amdhsa_next_free_spgr` directive in
 
 May be set at any time, e.g. manually set to zero at the start of each kernel.
 
-Code Object Directives
-~~~~~~~~~~~~~~~~~~~~~~
+Code Object Directives (-mattr=+code-object-v3)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 Directives which begin with ``.amdgcn`` are valid for all ``amdgcn``
 architecture processors, and are not OS-specific. Directives which begin with
@@ -4473,8 +4568,8 @@ terminated by an ``.end_amdhsa_kernel`` directive.
                                                                                             :ref:`amdgpu-amdhsa-compute_pgm_rsrc2-gfx6-gfx9-table`.
      ======================================================== ================ ============ ===================
 
-Example HSA Source Code
-~~~~~~~~~~~~~~~~~~~~~~~
+Example HSA Source Code (-mattr=+code-object-v3)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 Here is an example of a minimal assembly source file, defining one HSA kernel: