On 03/01/2013 02:02 AM, Aras Pranckevicius wrote:
Hi,opt_constant_variable was marking a variable as constant as long as there was exactly one constant assignment to it, but did not take into account that this assignment might be in a dynamic branch or a loop. Was happening on a fragment shader like this: uniform float mode; float func (float c) { if (mode == 2.0) return c; // was returning 0.1 after optimization! if (mode == 3.0) discard; if (mode == 10.0) c = 0.1; return c; } void main() { vec4 c = gl_FragCoord; c.x = func(c.x); gl_FragColor = c; } Now, looking further this optimization pass should also not mark variables as const if there was a dereference of them before that first assignment. I had code to do this (a hashtable that would track dereferences before assignment is done). But couldn't come up with a test case that would break the whole set of optimizations that Mesa does (lower jumps, or inlining, ... were getting in the way and hide the bug).
Good catch! There are a couple white-space issues in the patch, but I can fix those when I push it. I'll wait a bit for other people to give review comments. I'll probably also copy the above text into the commit message.
-- Aras Pranckevičius work: http://unity3d.com home: http://aras-p.info _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
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