Bug 9856

Summary:	rendering errors with arb_vp with swtnl when using optimization flags
Product:	Mesa	Reporter:	Roland Scheidegger <sroland>
Component:	Mesa core	Assignee:	mesa-dev
Status:	RESOLVED FIXED	QA Contact:
Severity:	normal
Priority:	medium
Version:	git
Hardware:	x86 (IA32)
OS:	All
Whiteboard:
i915 platform:		i915 features:

Description Roland Scheidegger 2007-02-02 10:43:47 UTC

t_vb_arbprogram.c seems to miscompile when using any optimization flags (even -O1) with recent gcc (tried 4.1.0 and 4.1.1, it does not happen with 3.4.6). There are no compiler warnings, but rendering artifacts may happen. It is very easily visible with the doom3 main title screen, when the planet zooms in there are lots of bogus black parts on the planet - once it's zoomed in it suddenly looks correct (similar glitches happen in the game the whole time).
Tested with r200 (tcl_mode 0) as well as standalone mesa (using +set r_renderer r200 for doom3).
Not sure what's going on, it could also be a compiler bug.

Comment 1 Roland Scheidegger 2007-02-02 17:29:30 UTC

forgot to mention, but the exact same thing happens when the codegen is used (with MESA_EXPERIMENTAL set to true, the glitches just render a lot faster...). It does not matter if t_vb_arbprogram_sse.c is compiled with optimization or not, it only depends on the optimization flags used for t_vb_arbprogram.c, even if codegen is used.

Comment 2 Roland Scheidegger 2007-02-05 12:38:59 UTC

Ok fixed. Turns out it's nowhere near as dramatic as it looked. It did NOT miscompile, apparently the -ffast-math option (actually it was -funsafe-math-optimizations) caused slightly different results to fixed function vertex transform because a different function (though mathematically equivalent) was used for the transformation (not with -O0 though, maybe the optimizer can't really do much in that case). Results have to be the same however according to ARB_vp spec if the position invariant option is used. No wonder I saw errors only in doom3 - there is a reason the spec mentions that John Carmack requested this option with invariance to fixed function :-).

Comment 3 Adam Jackson 2009-08-24 12:25:41 UTC

Mass version move, cvs -> git

Use of freedesktop.org services, including Bugzilla, is subject to our Code of Conduct. How we collect and use information is described in our Privacy Policy.