[Mesa-dev] [PATCH 00/10] glsl: Support unsized arrays in interface blocks.

[Jordan Justen]

Patches 1, 2 & 4 - 10:
Reviewed-by: Jordan Justen <jordan.l.justen at intel.com>

For 8, I replied with a non-essential question, and the same question
is relevant in patch 10.

For patch 3 I had that question (mentioned on irc) about ir having
ast/parser knowledge. I guess I'd like to think about this one a
little more.

-Jordan

On Fri, Sep 27, 2013 at 12:05 PM, Paul Berry <stereotype441 at gmail.com> wrote:
> Although it's not explicitly stated in the GLSL 1.50 spec, it is
> clearly implied that unsized arrays are allowed in interface blocks
> (the built-in interface gl_PerVertex contains an unsized array,
> gl_ClipDistance, and examples added in GLSL 4.30 make use of unsized
> arrays in interface blocks).
>
> From the client's point of view, unsized inside interface blocks work
> the same way as unsized arrays outside of interface blocks: they
> acquire a size at link time based on the maximum array element
> accessed (across all compilation units for a given shader stage), and
> then this acquired size is used to match interfaces from one shader
> stage to the next.
>
> Internally, however, things are a bit different, because Mesa's
> implementation of interface blocks makes heavy re-use of its
> implementation of structs.  Ideally I would have liked to keep track
> of the maximum array element accessed inside the data structure that
> stores the interface type, and I would have liked to update this data
> structure in place when the array sizes are acquired.  But this is
> unsafe because the implementation uses a flyweight pattern for types;
> at the time a struct or interface type is declared, it is looked up in
> a global hash table, and if a matching struct or interface type has
> previously been declared, the pointer is shared (even if the matching
> struct was used in a different shader, different thread, or different
> context).  As a result, any interface type in existence may be shared
> with an unknown set of shaders (some of which are possibly being
> compiled concurrently), so it is unsafe to modify the data structure.
> Therefore, instead, we track the maximum array element accessed inside
> the ir_variable class, and when the arrays acquire sizes we create a
> new interface type and walk through the IR updating the type of all
> the variables that refer to it.
>
> Patches 1-4 are preparatory work.  Patch 1 adds parser support for
> unsized arrays in interface blocks.  Patches 2 and 3 do some minor
> code reorganization so that in patch 7, we will be able to easily
> track the maximum element used in any array that appears in an
> interface block.  Patch 4 makes ir_variable::interface_type private
> and creates getter and setter methods for it; in patches 5 and 8, this
> will allow us to ensure than an invariant is preserved when the
> interface type changes.
>
> Patch 5 adds a new field, ir_variable::max_ifc_array_access, which
> keeps track of the maximum element used in any array that appears in
> an interface block.  Patch 6 adds code to ir_validate to make sure
> that the values in max_ifc_array_access are never greater than the
> sizes of sized arrays.  Patch 7 adds code to update
> max_ifc_array_access properly when an array is accessed.
>
> Patch 8 modifies the linker's array_sizing_visitor so that unsized
> arrays in named interface blocks acquire sizes at link time.  Patch 9
> modifies the linker's call_link_visitor so that if an interface block
> containing unsized arrays is used in multiple compilation units for
> the same shader stage, we use the maximum array access across all
> compilation units to assign the size.  Patch 10 modifies the linker's
> array_sizing_visitor so that unsized arrays in unnamed interface
> blocks acquire sizes at link time.
>
>
> [PATCH 01/10] glsl: Add parser support for unsized arrays in interface blocks.
> [PATCH 02/10] glsl: Link uniform-initializer-test with standalone_scaffolding.cpp.
> [PATCH 03/10] glsl: Move update of max_array_access into a virtual function on ir_rvalue.
> [PATCH 04/10] glsl: Make accessor functions for ir_variable::interface_type.
> [PATCH 05/10] glsl: Add an ir_variable::max_ifc_array_access field.
> [PATCH 06/10] glsl: Sanity check max_ifc_array_access in ir_validate::visit(ir_variable *).
> [PATCH 07/10] glsl: Update ir_variable::max_ifc_array_access properly.
> [PATCH 08/10] glsl/linker: Modify array_sizing_visitor to handle named interface blocks.
> [PATCH 09/10] glsl: Update call_link_visitor to update max_ifc_array_access.
> [PATCH 10/10] glsl: Modify array_sizing_visitor to handle unnamed interface blocks.
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