Few weeks ago I submitted this same series, that essentially expands the
existing validation of inter-shader build-in interfaces blocks, to also
consider blocks that have unused members and thus were optimized out at compile
time.
The original concern about this series was that forcing a link error on blocks
that have no used members was not a spec requirement, and thus would make the
linker behavior more restrictive than expected/necessary. Apparently, this is
not the case.
After filing a bug against the spec to clarify this, the position seems firm
that built-in block interfaces must match across shaders within a program,
regardless of usage of its members. These are the relevant spec quotations,
from OpenGL Shading Language 4.5:
Section 4.3.9 Interface Blocks:
"The block name (block-name) is used to match within shader interfaces: an
output block of one pipeline stage will be matched to an input block with the
same name in the subsequent pipeline stage."
Followed in the next paragraph by:
"Matched block names within a shader interface (as defined above) must
match in terms of having the same number of declarations with the same sequence
of types and the same sequence of member names, as well as having the same
member-wise layout qualification (see next section)."
Section 7.1 Built-In Language Variables:
"If multiple shaders using members of a built-in block belonging to the
same interface are linked together in the same program, they must all redeclare
the built-in block in the same way, as described in section 4.3.9 “Interface
Blocks” for interface-block matching, or a link-time error will result. If a
built-in block interface is formed across shaders in different programs, the
shaders must all redeclare the built-in block in the same way (as described for
a single program), or the values passed along the interface are undefined."
There is no explicit language for blocks with unused members, hence we must
assume all re-declared blocks are subject to the restrictions above.
Honestly, I think it is unfortunate that we need to carry otherwise unused
symbols from compile-time to link-time, just to perform this validation.
However, the code is pretty simple and we get to factorize a couple of routines
too. Also, I see value in catching a potential shader error early.
Eduardo
Eduardo Lima Mitev (3):
glsl_parser_extra: Add utility to copy symbols between symbol tables
glsl: Use the utility function to copy symbols between symbol tables
glsl/linker: Check that re-declared, inter-shader built-in blocks
match
src/compiler/glsl/glsl_parser_extras.cpp | 53 ++++++++++++++++++++---------
src/compiler/glsl/glsl_parser_extras.h | 5 +++
src/compiler/glsl/link_interface_blocks.cpp | 33 +++++++++++++++++-
src/compiler/glsl/linker.cpp | 16 ++-------
4 files changed, 77 insertions(+), 30 deletions(-)
--
2.11.0
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