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).
--
Aras Pranckevičius
work: http://unity3d.com
home: http://aras-p.info
glsl-constant-variable-fix.diff
Description: Binary data
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