Hi, as we found out, the same issue exists and for Vulkan (original description can be found in this issue -> https://bugs.freedesktop.org/show_bug.cgi?id=107088 )
Patch was also sent for review:
commit 00fc56a68d21d7aa91b95f0eaacba59a96c466f5 (HEAD -> master)
Author: Danylo Piliaiev <firstname.lastname@example.org>
Date: Fri Jul 20 12:54:42 2018 +0300
anv: Disable dual source blending when shader doesn't support it on gen8+
Dual source blending behaviour is undefined when shader doesn't
have second color output.
"If SRC1 is included in a src/dst blend factor and
a DualSource RT Write message is not used, results
are UNDEFINED. (This reflects the same restriction in DX APIs,
where undefined results are produced if “o1” is not written
by a PS – there are no default values defined)."
Dismissing fragment in such situation leads to a hang on gen8+
if depth test in enabled.
Since blending cannot be gracefully fixed in such case and the result
is undefined - blending is simply disabled.
v2 (Jason Ekstrand):
- Apply the workaround to each individual entry
- Emit a warning through debug_report
Signed-off-by: Danylo Piliaiev <email@example.com>
Reviewed-by: Jason Ekstrand <firstname.lastname@example.org>
Reviewed-by: Kenneth Graunke <email@example.com>