[Mesa-dev] Optimizations in mesa shader compiler

[Segovia, Benjamin]

To be more precise,
- The shader compiler present in src/mesa/slang is used.

- The glsl shader (randomly taken on the net) is:
void main(){
  const float PI = 3.14159265358979323846264;
  const float angle = 45.0;
  const float rad_angle = angle*PI/180.0;
  vec4 a = gl_Vertex;
  vec4 b = a;

  b.x = a.x*cos(rad_angle) - a.y*sin(rad_angle);
  b.y = a.y*cos(rad_angle) + a.x*sin(rad_angle);
  gl_Position = gl_ModelViewProjectionMatrix*b;
}

- IR Output produced is:
# Vertex Program/Shader 1
  0: MOV TEMP[0].x, CONST[0].xxxx;
  1: MUL TEMP[1].x, CONST[0].yyyy, TEMP[0].xxxx;
  2: RCP TEMP[1].z, CONST[0].zzzz;
  3: MUL TEMP[0].w, TEMP[1].xxxx, TEMP[1].zzzz;
  4: MOV TEMP[0].z, TEMP[0].wwww;
  5: MOV TEMP[1].xz, INPUT[0];
  6: MOV TEMP[1].xzw, INPUT[0];
  7: COS TEMP[0].w, TEMP[0].wwww;
  8: MUL TEMP[2].x, INPUT[0].xxxx, TEMP[0].wwww;
  9: SIN TEMP[0].w, TEMP[0].zzzz;
 10: MUL TEMP[2].y, INPUT[0].yyyy, TEMP[0].wwww;
 11: SUB TEMP[1].x, TEMP[2].xxxx, TEMP[2].yyyy;
 12: COS TEMP[2].x, TEMP[0].zzzz;
 13: SIN TEMP[2].y, TEMP[0].zzzz;
 14: MUL TEMP[2].z, INPUT[0].xxxx, TEMP[2].yyyy;
 15: MAD TEMP[2].y, INPUT[0].yyyy, TEMP[2].xxxx, TEMP[2].zzzz;
 16: MUL TEMP[0], STATE[2], TEMP[2].yyyy;
 17: MAD TEMP[2], STATE[1], TEMP[1].xxxx, TEMP[0];
 18: MAD TEMP[0], STATE[3], TEMP[1].zzzz, TEMP[2];
 19: MAD TEMP[2], STATE[4], TEMP[1].wwww, TEMP[0];
 20: MOV OUTPUT[0], TEMP[2];
 21: END
*/
/* Parameters / constants */
/*
dirty state flags: 0x3
param[0] sz=3 CONST (null) = {3.14, 45, 180, 3.14}
param[1] sz=4 STATE state.matrix.mvp.transpose.row[0] = {0, 0, 0, 0}
param[2] sz=4 STATE state.matrix.mvp.transpose.row[1] = {0, 0, 0, 0}
param[3] sz=4 STATE state.matrix.mvp.transpose.row[2] = {0, 0, 0, 0}
param[4] sz=4 STATE state.matrix.mvp.transpose.row[3] = {0, 0, 0, 0}
*/

- Finally, Gen code also includes the constant computations in the shader.

Ben
 
________________________________________
From: mesa-dev-bounces+benjamin.segovia=intel.com at lists.freedesktop.org [mesa-dev-bounces+benjamin.segovia=intel.com at lists.freedesktop.org] On Behalf Of Segovia, Benjamin [benjamin.segovia at intel.com]
Sent: Tuesday, July 13, 2010 4:11 PM
To: mesa-dev at lists.freedesktop.org
Subject: [Mesa-dev] Optimizations in mesa shader compiler

Hello all,

I just looked at the (intermediate) code produced by the shader compiler. In the last version, I did not find anything on constant propagation and constant computations. In the Intel current driver, the final gen code produces an ugly sequence of computations of constant values (known at compile time). I would like to spend some time on it but I am wondering if it is still supported or if other shader compilers are going to replace it.

Cheers,
Ben