GLSL source for geometry shader 3:
#version 330

layout(triangles) in;
layout(triangle_strip, max_vertices = 3) out;

in gl_PerVertex
{
    vec4 gl_Position;
} gl_in[];

in vec4 v_colour[];

out gl_PerVertex
{
    vec4 gl_Position;
};

out vec4 g_colour;

void main(void)
{
    for (int i = 0; i < gl_in.length(); ++i) {
        gl_Position = gl_in[i].gl_Position;
        g_colour = v_colour[i];
        EmitVertex();
    }
    EndPrimitive();
}

GLSL IR for shader 3:
(
(declare (shader_out flat) int gl_PrimitiveID)
(declare (shader_in flat) int gl_PrimitiveIDIn)
(declare (shader_out ) int gl_Layer)
(declare (shader_out ) vec4 gl_Position)
(declare (shader_in ) (array gl_PerVertex 3) gl_in)
(declare (uniform ) (array vec4 56) gl_CurrentAttribFragMESA)
(declare (uniform ) (array vec4 33) gl_CurrentAttribVertMESA)
(declare (uniform ) gl_DepthRangeParameters gl_DepthRange)
(declare (uniform ) int gl_NumSamples)
(declare () int gl_MaxGeometryVaryingComponents)
(declare () int gl_MaxGeometryUniformComponents)
(declare () int gl_MaxGeometryTotalOutputComponents)
(declare () int gl_MaxGeometryOutputVertices)
(declare () int gl_MaxGeometryTextureImageUnits)
(declare () int gl_MaxFragmentInputComponents)
(declare () int gl_MaxGeometryOutputComponents)
(declare () int gl_MaxGeometryInputComponents)
(declare () int gl_MaxVertexOutputComponents)
(declare () int gl_MaxVaryingComponents)
(declare () int gl_MaxClipDistances)
(declare () int gl_MaxFragmentUniformComponents)
(declare () int gl_MaxVaryingFloats)
(declare () int gl_MaxVertexUniformComponents)
(declare () int gl_MaxDrawBuffers)
(declare () int gl_MaxTextureImageUnits)
(declare () int gl_MaxCombinedTextureImageUnits)
(declare () int gl_MaxVertexTextureImageUnits)
(declare () int gl_MaxVertexAttribs)
(declare (shader_in ) (array vec4 3) v_colour)
(declare (shader_out ) vec4 g_colour)
(function main
  (signature void
    (parameters
    )
    (
      (declare () int i)
      (assign  (x) (var_ref i)  (constant int (0)) ) 
      (loop (
        (if (expression bool >= (var_ref i) (constant int (3)) ) (
          break
        )
        ())

        (assign  (xyzw) (var_ref gl_Position)  (record_ref (array_ref (var_ref gl_in) (var_ref i) )  gl_Position) ) 
        (assign  (xyzw) (var_ref g_colour)  (array_ref (var_ref v_colour) (var_ref i) ) ) 
        (call EmitVertex  ())

        (assign  (x) (var_ref i)  (expression int + (var_ref i) (constant int (1)) ) ) 
      ))

      (call EndPrimitive  ())

    ))

)

(function EmitVertex
  (signature void
    (parameters
    )
    (
    ))

)

(function EndPrimitive
  (signature void
    (parameters
    )
    (
    ))

)


)

../../../src/mesa/state_tracker/st_glsl_to_tgsi.cpp:2157:visit: Assertion `var->data.location != -1' failed.

Program received signal SIGTRAP, Trace/breakpoint trap.
0x00007ffff21613b6 in _debug_assert_fail (expr=<optimized out>, file=<optimized out>, line=<optimized out>, function=<optimized out>) at ../../../../src/gallium/auxiliary/util/u_debug.c:309
309	   os_abort();
(gdb) bt
#0  0x00007ffff21613b6 in _debug_assert_fail (expr=<optimized out>, file=<optimized out>, line=<optimized out>, function=<optimized out>)
    at ../../../../src/gallium/auxiliary/util/u_debug.c:309
#1  0x00007ffff1fd4a85 in glsl_to_tgsi_visitor::visit (this=0x7b8680, ir=<optimized out>) at ../../../src/mesa/state_tracker/st_glsl_to_tgsi.cpp:2157
#2  0x00007ffff1fd709c in glsl_to_tgsi_visitor::visit (this=0x7b8680, ir=0x7c2b90) at ../../../src/mesa/state_tracker/st_glsl_to_tgsi.cpp:2205
#3  0x00007ffff1fe68ce in glsl_to_tgsi_visitor::visit (this=0x7b8680, ir=0x7c2c00) at ../../../src/mesa/state_tracker/st_glsl_to_tgsi.cpp:2458
#4  0x00007ffff1fd2d27 in glsl_to_tgsi_visitor::visit (this=0x7b8680, ir=<optimized out>) at ../../../src/mesa/state_tracker/st_glsl_to_tgsi.cpp:1202
#5  0x00007ffff2096955 in visit_exec_list (list=<optimized out>, visitor=visitor@entry=0x7b8680) at ../../../src/glsl/ir.cpp:1738
#6  0x00007ffff1ff2a46 in get_mesa_program (shader=0x7c18a0, shader_program=0x7bf120, ctx=0x7729c0) at ../../../src/mesa/state_tracker/st_glsl_to_tgsi.cpp:5240
#7  st_link_shader (ctx=0x7729c0, prog=0x7bf120) at ../../../src/mesa/state_tracker/st_glsl_to_tgsi.cpp:5474
#8  0x00007ffff200e737 in _mesa_glsl_link_shader (ctx=0x7729c0, prog=0x7bf120) at ../../../src/mesa/program/ir_to_mesa.cpp:3082
#9  0x00007ffff1f0cd29 in link_program (program=4, ctx=0x7729c0) at ../../../src/mesa/main/shaderapi.c:915
#10 _mesa_create_shader_program (separate=1 '\001', strings=<optimized out>, count=<optimized out>, type=<optimized out>, ctx=0x7729c0) at ../../../src/mesa/main/shaderapi.c:1847
#11 _mesa_CreateShaderProgramv (type=<optimized out>, count=<optimized out>, strings=<optimized out>) at ../../../src/mesa/main/shaderapi.c:1920
#12 0x000000000040189d in main () at main.c:113