From: Kenneth Graunke Date: Sat, 15 Oct 2016 00:59:36 +0000 (-0700) Subject: i965: Allocate at least some URB space even when max_vertices = 0. X-Git-Tag: upstream/17.1.0~4087 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=a41f5dcb141a11ca5ca0c765c305027b0f0b609e;p=platform%2Fupstream%2Fmesa.git i965: Allocate at least some URB space even when max_vertices = 0. Allocating zero URB space is a really bad idea. The hardware has to give threads a handle to their URB space, and threads have to use that to terminate the thread. Having it be an empty region just breaks a lot of assumptions. Hence, why we asserted that it isn't possible. Unfortunately, it /is/ possible prior to Gen8, if max_vertices = 0. In theory a geometry shader could do SSBO/image access and maybe still accomplish something. In reality, this is tripped up by conformance tests. Gen8+ already avoids this problem by placing the vertex count DWord in the URB entry header. This fixes things on earlier generations. Cc: mesa-stable@lists.freedesktop.org Signed-off-by: Kenneth Graunke Reviewed-by: Anuj Phogat Tested-by: Ian Romanick --- diff --git a/src/mesa/drivers/dri/i965/brw_vec4_gs_visitor.cpp b/src/mesa/drivers/dri/i965/brw_vec4_gs_visitor.cpp index 900d9d3..3894a63 100644 --- a/src/mesa/drivers/dri/i965/brw_vec4_gs_visitor.cpp +++ b/src/mesa/drivers/dri/i965/brw_vec4_gs_visitor.cpp @@ -781,7 +781,13 @@ brw_compile_gs(const struct brw_compiler *compiler, void *log_data, if (compiler->devinfo->gen >= 8) output_size_bytes += 32; - assert(output_size_bytes >= 1); + /* Shaders can technically set max_vertices = 0, at which point we + * may have a URB size of 0 bytes. Nothing good can come from that, + * so enforce a minimum size. + */ + if (output_size_bytes == 0) + output_size_bytes = 1; + unsigned max_output_size_bytes = GEN7_MAX_GS_URB_ENTRY_SIZE_BYTES; if (compiler->devinfo->gen == 6) max_output_size_bytes = GEN6_MAX_GS_URB_ENTRY_SIZE_BYTES;