Macro gets expanded twice, leading to unexpected generated code.

[jeroenbakker-atmind]

Hi,

Blender developer here. Currently we are developing our Vulkan back-end. We use intensively macros to be able to cross compile between OpenGL/Vulkan/Metal and also for migrating between internal feature sets.

When compiling the next vertex shader using glslc fails. For now we are using

shaderc v2021.3 v2021.3
spirv-tools v2021.4 v2021.4
glslang 11.1.0-316-g600c5037

To reproduce you can use glslc -fshader-stage=vertex ./vertex.glsl to validate the error.
./vertex.glsl:68: error: '' : syntax error, unexpected LEFT_PAREN, expecting IDENTIFIER

I did search for similar issues, but didn't see them. Sorry if I added a new one by mistake or has already been resolved up-stream.

#version 450

#define drw_view drw_view_[drw_view_id]

/* Single-view case (default). */
#define drw_view_id 0
#define DRW_VIEW_LEN 1
#define DRW_VIEW_SHIFT 0

struct ViewMatrices {
  mat4 viewmat;
  mat4 winmat;
};

#define ViewMatrix drw_view.viewmat
#define ProjectionMatrix drw_view.winmat

/** \} */

/* Pass Resources. */
layout(binding = 0, std140) uniform drw_view_ {
  ViewMatrices _drw_view_[DRW_VIEW_LEN];
};
#define drw_view_ (_drw_view_)

/* Push Constants. */
layout(push_constant) uniform constants {
  vec3 pPosition;
  float pSize;
  vec4 pColor;
}
PushConstants;
#define pPosition (PushConstants.pPosition)
#define pSize (PushConstants.pSize)
#define pColor (PushConstants.pColor)

/* Inputs. */
layout(location = 0) in vec3 pos;

/* Interfaces. */
layout(location = 0) out flat vec4 finalColor;

/** Transform shortcuts. */
/* Rule of thumb: Try to reuse world positions and normals because converting
 * through viewspace will always be decomposed in at least 2 matrix operation.
 */
#define point_world_to_ndc(p) (ProjectionMatrix * (ViewMatrix * vec4(p, 1.0)))

void main() {
#if 0
  /* Use local variable to workaround macro unrolling issue in Spir-V. */
  vec3 pos = pPosition;
  gl_Position = point_world_to_ndc(pos);
#else
  /* Unrolling fails when unrolling with

  ./vertex.glsl:69: error: '' :  syntax error, unexpected LEFT_PAREN, expecting
IDENTIFIER.

  shaderc v2021.3 v2021.3
  spirv-tools v2021.4 v2021.4
  glslang 11.1.0-316-g600c5037

  Target: SPIR-V 1.0
  */

  gl_Position = point_world_to_ndc(pPosition);
#endif
  finalColor = pColor;
  gl_PointSize = pSize;
}

[jeroenbakker-atmind]

Another workaround is to change the Push constant defines fe #define pcPosition (PushConstants.pPosition).

[LazyDodo]

seems like pPosition get expanded twice , running glslangvalidator -E on this shader gave:

gl_Position =((((_drw_view_)[0]). winmat)*((((_drw_view_)[0]). viewmat)* vec4(((PushConstants .(PushConstants . pPosition))), 1.0)));
for the failing case.

[dneto0]

Still reproduces with top of tree.

Putting the source into x.vert and doing this:

  glslc -E x.vert

Produces output with this in it:

   gl_Position =((_drw_view_)[0]. winmat *((_drw_view_)[0]. viewmat * vec4((PushConstants .(PushConstants . pPosition)), 1.0)));

This also reproduces with glslangValidator itself:

$ glslangValidator -V x.vert -o x.spv
x.vert
ERROR: x.vert:67: '' :  syntax error, unexpected LEFT_PAREN, expecting IDENTIFIER
ERROR: 1 compilation errors.  No code generated.


SPIR-V is not generated for failed compile or link

[dneto0]

Preprocessor expansion with glslangValidator shows the same bad line:

$ glslangValidator -E x.vert |grep pPosition
  vec3 pPosition;
  gl_Position =((_drw_view_)[0]. winmat *((_drw_view_)[0]. viewmat * vec4((PushConstants .(PushConstants . pPosition)), 1.0)));

[dneto0]

This is a minimal reproducer:

#version 450

layout(push_constant) uniform constants {
  vec4 pPosition;
}
PushConstants;
#define pPosition (PushConstants.pPosition)

layout(location=0) out vec3 o;

#define m(p)  vec4(p,1.0);

void main() {
  gl_Position = m(pPosition);
}

glslangValidator -E y.vert shows:

$ glslangValidator -E y.vert
#version 450

layout(push_constant)uniform constants {
  vec4 pPosition;
}
PushConstants;


layout(location = 0)out vec3 o;



void main(){
  gl_Position = vec4((PushConstants .(PushConstants . pPosition)), 1.0);;
}

So this would be an upstream bug.

I've transferred this to KhronosGroup/glslang#3112

[jeroenbakker-atmind]

Another workaround is to change the Push constant defines fe #define pcPosition (PushConstants.pPosition).

[LazyDodo]

seems like pPosition get expanded twice , running glslangvalidator -E on this shader gave:

gl_Position =((((_drw_view_)[0]). winmat)*((((_drw_view_)[0]). viewmat)* vec4(((PushConstants .(PushConstants . pPosition))), 1.0)));
for the failing case.

[dneto0]

Still reproduces with top of tree.

Putting the source into x.vert and doing this:

  glslc -E x.vert

Produces output with this in it:

   gl_Position =((_drw_view_)[0]. winmat *((_drw_view_)[0]. viewmat * vec4((PushConstants .(PushConstants . pPosition)), 1.0)));

This also reproduces with glslangValidator itself:

$ glslangValidator -V x.vert -o x.spv
x.vert
ERROR: x.vert:67: '' :  syntax error, unexpected LEFT_PAREN, expecting IDENTIFIER
ERROR: 1 compilation errors.  No code generated.


SPIR-V is not generated for failed compile or link

[dneto0]

Preprocessor expansion with glslangValidator shows the same bad line:

$ glslangValidator -E x.vert |grep pPosition
  vec3 pPosition;
  gl_Position =((_drw_view_)[0]. winmat *((_drw_view_)[0]. viewmat * vec4((PushConstants .(PushConstants . pPosition)), 1.0)));

[dneto0]

This is a minimal reproducer:

#version 450

layout(push_constant) uniform constants {
  vec4 pPosition;
}
PushConstants;
#define pPosition (PushConstants.pPosition)

layout(location=0) out vec3 o;

#define m(p)  vec4(p,1.0);

void main() {
  gl_Position = m(pPosition);
}

glslangValidator -E y.vert shows:

$ glslangValidator -E y.vert
#version 450

layout(push_constant)uniform constants {
  vec4 pPosition;
}
PushConstants;


layout(location = 0)out vec3 o;



void main(){
  gl_Position = vec4((PushConstants .(PushConstants . pPosition)), 1.0);;
}

So this would be an upstream bug.

I've transferred this to KhronosGroup/glslang#3112