bug.glsl

#version 100
#define SAMPLER_COUNT 2
uniform sampler2D samplers[SAMPLER_COUNT];
void main() {
  vec4 sum = vec4(0.0);
  for(int i = 0; i < SAMPLER_COUNT; i++) {
    sum += samplers[i];
  }
  gl_FragColor = sum;
}

$ glslopt -2 -f bug.glsl
Failed to compile bug.glsl:

(7,9): error: sampler arrays indexed with non-constant expressions is forbidden in GLSL 1.30 and later
(7,2): error: operands to arithmetic operators must be numeric

However, according to the GLSL ES 2.0 spec Page 109 (115 in PDF): https://www.khronos.org/registry/OpenGL/specs/es/2.0/GLSL_ES_Specification_1.00.pdf:

5 Indexing of Arrays, Vectors and Matrices

[...]
The following are constant-index-expressions:

• Constant expressions
• Loop indices as defined in section 4
• [...]

Samplers

GLSL ES 1.00 supports both arrays of samplers and arrays of structures which contain samplers. In both these cases, for ES 2.0, support for indexing with a constant-index-expression is mandated but support for indexing with other values is not mandated.

So this is a bug, because I'm using a constant-index-expressions, for which support is mandated by the GLSL spec.

I did look into it, and the broken check is here:

This bug does not exist in a rebased fork with a more recent mesa: https://github.com/jamienicol/glsl-optimizer/
The fixed check is here.