find the location of texture uniform

Hi ,here is my glsl code

#version 400
in vec4 ex_Color;
in vec4 ex_Pos;
out vec4 FragColor;
uniform sampler2D RayStartPoint;
uniform sampler2D RayStopPoint;
void main()
  vec4 temp = ex_Color;
  vec2 texc = ((ex_Pos.xy / ex_Pos.w) + 1.0f )/2.0f ;  
  vec4 startPosition  = texture(RayStartPoint, texc) ;
  vec4 stopPosition  = texture2D(RayStopPoint, texc);
   temp.w = 1 ;   
 // FragColor = startPosition ;
	FragColor = stopPosition ;
 // FragColor = temp ;
 //  FragColor = stopPosition -  startPosition ;

my program could find the first uniform location,but can’t find the second. the function “glGetUniformLocation” just return -1
anyone had encountered similar problem?

You are not using the uniform in the code so it is optimised away. You always have to be able to cope with -1 return. It is usually any error - unless you are testing when it is really a pain!

Cross-posting isn’t helping.