glsl: Indirect array indexing on non-last SSBO member must fail compilation

Graphics / Mesa 3D Graphics Library / Mesa - Iago Toral Quiroga [igalia.com] - 20 October 2016 01:26 UTC

After the changes in comit 5b2675093e863a52, we moved this check to the linker, but the spec expects this to be checked at compile-time. There are dEQP tests that expect an error at compile time and the spec seems to confirm that expectation:

"Except for the last declared member of a shader storage block (section 4.3.9 “Interface Blocks”), the size of an array must be declared (explicitly sized) before it is indexed with anything other than an integral constant expression. The size of any array must be declared before passing it as an argument to a function. Violation of any of these rules result in compile-time errors. It is legal to declare an array without a size (unsized) and then later redeclare the same name as an array of the same type and specify a size, or index it only with integral constant expressions (implicitly sized)."

Commit 5b2675093e863a52 tries to take care of the case where we have implicitly sized arrays in SSBOs and it does so by checking the max_array_access field in ir_variable during linking. In this patch we change the approach: we look for indirect access on SSBO arrays, and when we find one, we emit a compile-time error if the accessed member is not the last in the SSBO definition.

There is a corner case that the specs do not address directly though and that dEQP checks for: the case of an unsized array in an SSBO definition that is not defined last but is never used in the shader code either. The following dEQP tests expect a compile-time error in this scenario:

dEQP-GLES31.functional.debug.negative_coverage.callbacks.shader.compile_compute_shader dEQP-GLES31.functional.debug.negative_coverage.get_error.shader.compile_compute_shader dEQP-GLES31.functional.debug.negative_coverage.log.shader.compile_compute_shader

However, since the unsized array is never used it is never indexed with a non-constant expression, so by the spec quotation above, it should be valid and the tests are probably incorrect.

3da08e1 glsl: Indirect array indexing on non-last SSBO member must fail compilation
src/compiler/glsl/ast_array_index.cpp | 14 ++++++++++++++
src/compiler/glsl/link_uniform_blocks.cpp | 8 +-------
2 files changed, 15 insertions(+), 7 deletions(-)

Upstream: cgit.freedesktop.org

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