[Mesa-dev] [PATCH 00/24] Initial gl_spirv and spirv_extensions support in Mesa and i965

Eduardo Lima Mitev elima at igalia.com
Wed Nov 15 13:22:03 UTC 2017


This series is the first chunk of our on-going work to support GL_ARB_gl_spirv [1] and GL_ARB_spirv_extensions [2] in Mesa and i965. It adds API entry-points, API error checking, most of driver-agnostic setup and housekeeping, and a few basic i965 bits. It is based off initial work that Nicolai Hähnle did back in July.

In the case of GL_ARB_spirv_extensions, we consider our work on this extension to be completed.

For GL_ARB_gl_spirv, this is the high level explanation of what we do:

* When the user calls glShaderBinary() with a SPIR-V binary, we mark the shader as a SPIR-V shader and save the binary module within it.

* Upon a call to glSpecializeShaderARB(), we perform a pass over the saved binary module to validate that the given specialization constants and entry point are ok. For this, we use a modified version of spirv_to_nir() that doesn't generate any NIR, but simply performs the validation we need. If everything went ok, we then save the specialization constants and entry point within the shader object as well.

* Upon program linking, and before calling driver-specific LinkShader(), we generate gl_linked_shader objects and associate them with the SPIR-V data that has been recorded in gl_shader (namely: the binary module, the specialization constants and the entry point name).

* We also introduce a convenient spirv_to_nir() wrapper for backends that use NIR.

This is all this series does. At this point, driver-specific linkers have all the SPIR-V information they need (attached to the gl_shader and gl_linked_shader objects of a program) to implement whatever linking strategy they choose. For i965, we are planning to go for a (mostly) pure NIR linking approach (see below).

This is the series' logical break down:

- Patch 1 introduces the extension in Mesa and adds 'mesa/main/glspirv.c/h' files to hold its implementation.

- Patch 2 adds a flag to gl_shader to tell SPIR-V and GLSL shaders apart.

- Patch 3 adds error checks introduced by the extension.

- Patches 4 to 6 make glShaderBinary() load SPIR-V, associating the SPIR-V binary with the shader for later use.

- Patches 7 to 9 add SPIR-V capabilities to a GL context. This information is an extension requirement. In our case, we already fill it up for i965.

- Patches 10 to 14 implement GL_ARB_spirv_extensions.

- Patches 15 and 16 implement glSpecializeShaderARB().

- Patches 17 to 22 fork the linking code for GLSL or SPIR-V programs, to avoid using the GLSL linker on SPIR-V shaders. The GLSL linker expects GLSL-IR to be present, and that's NULL for SPIR-V shaders.

- Patches 23 and 24 do the same as above but for i965, plus also generate the NIR out of each SPIR-V shader.

A tree of this series can be found at <https://github.com/Igalia/mesa/commits/arb_gl_spirv-series1-v1>.

A tree of the larger branch from which this series is taken can be found at <https://github.com/Igalia/mesa/commits/wip/igalia/arb_gl_spirv>. Note that this is still very experimental and will change a lot constantly.

What's our plan going forward?

In Mesa we have a single linker that is heavily interwined with GLSL-IR. So, if we want to link SPIR-V shaders, we have basically two approaches:

1. Convert the SPIR-V to GLSL-IR and reuse the existing linker: Introduces yet another conversion in the shader compilation process, but allows us to reuse a battle-tested linker.

2. Write a new linker: Obviously a lot of work.

Or use a combination of the two approaches, a mixed (or incremental) solution where we aim at writing a new linker, but for specific cases and/or temporarily we generate some minimal GLSL-IR that would allow us to reuse hard-to-rewrite parts of the existing GLSL linker.

After spending weeks prototyping different solutions, we have more or less settled for a mixed approach: write a pure NIR linker from scratch, that will reuse parts of the GLSL linker, but trying to avoid generating any GLSL-IR to feed the GLSL linker directly (doing that only when really needed).

We have prototyped some bits of this NIR linker already with a promising degree of success. At this point, we are confident that with this mixed approach we can write clean, efficient linking code; while at the same time have the flexibility to use the current GLSL linker to fill gaps.

If you are interested in more details about our approach, we encourage you to check the snapshot of our development branch at [3]. We would really appreaciate early feedback! (don't forget to MESA_EXTENSION_OVERRIDE="GL_ARB_gl_spirv").

Another deciding factor was recent discussions in Mesa, which suggests that a NIR linker can be useful to other backends, or for other purposes such as a later-stage shader cache. There is also the work Timothy started, which aligns well and complements what we need for GL_ARB_gl_spirv.

Another important aspect is testing, and here the work Ian is doing to generate SPIR-V binaries from GLSL is crucial. It will allow us to feed the NIR linker with a much larger set of shaders. We look forward to incorporate this conversion in our code-path and development workflow.

There is obviously a lot of work ahead to have a NIR linker at the same level of quality as the GLSL linker. Ideally, this would be a joint effort by those in the community who see value in having a pure NIR linker.

Thanks for reviewing!


[1] https://www.khronos.org/registry/OpenGL/extensions/ARB/ARB_gl_spirv.txt
[2] https://www.khronos.org/registry/OpenGL/extensions/ARB/ARB_spirv_extensions.txt
[3] https://github.com/Igalia/mesa/commits/wip/igalia/arb_gl_spirv

Alejandro Piñeiro (8):
  spirv_extensions: rename nir_spirv_supported_extensions
  i965: initialize SPIR-V capabilities
  spirv_extensions: add GL_ARB_spirv_extensions boilerplate
  spirv_extensions: add list of extensions and to_string method
  spirv_extensions: define spirv_extensions_supported
  spirv_extensions: add spirv_supported_extensions on gl_constants
  spirv_extensions: i965: initialize SPIR-V extensions
  nir/spirv: add gl_spirv_validation method

Eduardo Lima Mitev (9):
  mesa/glspirv: Add struct gl_shader_spirv_data
  mesa/main: Add a 'spirv' flag to gl_shader_program_data
  mesa/glspirv: Add a _mesa_spirv_link_shaders() placeholder
  mesa/program: Link SPIR-V shaders using the SPIR-V code-path
  mesa: Add a reference to gl_shader_spirv_data to gl_linked_shader
  mesa/glspirv: Create gl_linked_shader objects for a SPIR-V program
  mesa/glspirv: Add a _mesa_spirv_to_nir() function
  i965: Call spirv_to_nir() instead of glsl_to_nir() for SPIR-V shaders
  i965: Don't call process_glsl_ir() for SPIR-V shaders

Nicolai Hähnle (7):
  mesa: add GL_ARB_gl_spirv boilerplate
  mesa: add gl_shader::SpirVBinary and getter
  mesa: refuse to compile SPIR-V shaders or link mixed shaders
  mesa/glspirv: Add struct gl_spirv_module
  mesa: implement SPIR-V loading in glShaderBinary
  mesa: add gl_constants::SpirVCapabilities
  mesa: Implement glSpecializeShaderARB

 src/amd/vulkan/radv_shader.c                |   4 +-
 src/compiler/Makefile.sources               |   2 +
 src/compiler/spirv/nir_spirv.h              |  11 +-
 src/compiler/spirv/spirv_extensions.c       |  90 ++++++++
 src/compiler/spirv/spirv_extensions.h       |  81 +++++++
 src/compiler/spirv/spirv_to_nir.c           | 160 ++++++++++++-
 src/compiler/spirv/vtn_private.h            |   2 +-
 src/intel/vulkan/anv_pipeline.c             |   4 +-
 src/mapi/glapi/gen/ARB_gl_spirv.xml         |  21 ++
 src/mapi/glapi/gen/ARB_spirv_extensions.xml |  13 ++
 src/mapi/glapi/gen/Makefile.am              |   2 +
 src/mapi/glapi/gen/gl_API.xml               |   6 +
 src/mapi/glapi/gen/gl_genexec.py            |   1 +
 src/mesa/Makefile.sources                   |   4 +
 src/mesa/drivers/dri/i965/brw_context.c     |  29 +++
 src/mesa/drivers/dri/i965/brw_link.cpp      |   3 +-
 src/mesa/drivers/dri/i965/brw_program.c     |   9 +-
 src/mesa/main/context.c                     |   3 +
 src/mesa/main/extensions_table.h            |   2 +
 src/mesa/main/get.c                         |   6 +
 src/mesa/main/get_hash_params.py            |   3 +
 src/mesa/main/getstring.c                   |   7 +
 src/mesa/main/glspirv.c                     | 345 ++++++++++++++++++++++++++++
 src/mesa/main/glspirv.h                     | 108 +++++++++
 src/mesa/main/mtypes.h                      |  27 +++
 src/mesa/main/shaderapi.c                   |  56 ++++-
 src/mesa/main/shaderobj.c                   |   3 +
 src/mesa/main/spirvextensions.c             |  60 +++++
 src/mesa/main/spirvextensions.h             |  49 ++++
 src/mesa/main/tests/dispatch_sanity.cpp     |   3 +
 src/mesa/program/ir_to_mesa.cpp             |  24 +-
 31 files changed, 1111 insertions(+), 27 deletions(-)
 create mode 100644 src/compiler/spirv/spirv_extensions.c
 create mode 100644 src/compiler/spirv/spirv_extensions.h
 create mode 100644 src/mapi/glapi/gen/ARB_gl_spirv.xml
 create mode 100644 src/mapi/glapi/gen/ARB_spirv_extensions.xml
 create mode 100644 src/mesa/main/glspirv.c
 create mode 100644 src/mesa/main/glspirv.h
 create mode 100644 src/mesa/main/spirvextensions.c
 create mode 100644 src/mesa/main/spirvextensions.h


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