Looks like opt_vectorize is too eager on texture lookups. For example, a shader like this (which does a color correction effect by looking up R,G,B channels into a ramp texture):

uniform sampler2D _MainTex;
uniform sampler2D _RampTex;
varying vec2 varUV;
void main()
{
  vec4 orig = texture2D (_MainTex, varUV);
  float rr = texture2D (_RampTex, orig.xx).x;
  float gg = texture2D (_RampTex, orig.yy).y;
  float bb = texture2D (_RampTex, orig.zz).z;
  vec4 color = vec4 (rr, gg, bb, orig.w);
  gl_FragData[0] = color;
}

These 3 lookups effectively get vectorized into something like a:

  t.xyz = texture2DProj (_RampTex, t.xyz).xyz;


I can make this bug go away by stopping vectorizing on texture samples, i.e. adding something like this to opt_vectorize.cpp:


/**
 * Upon entering an ir_texture, remove the current assignment from
 * further consideration. Vectorizing multiple texture lookups into one
 * is wrong.
 */
ir_visitor_status
ir_vectorize_visitor::visit_enter(ir_texture *)
{
   this->current_assignment = NULL;
   return visit_continue_with_parent;
}