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Compiler-Assisted Optimization for Graphics

Compiler-Assisted Optimization for Graphics. Paul Arthur Navrátil The University of Texas at Austin. Motivation: OpenGL Extensions. Hardware manufacturers create acceleration features for market advantage Not all extensions supported on all hardware

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Compiler-Assisted Optimization for Graphics

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  1. Compiler-Assisted Optimization for Graphics Paul Arthur Navrátil The University of Texas at Austin

  2. Motivation: OpenGL Extensions • Hardware manufacturers create acceleration features for market advantage • Not all extensions supported on all hardware • 300+ extensions in OpenGL Extension registry • ~90 extensions supported by NVIDIA NV3x • ~75 extensions supported by ATI RADEON 9x00 • Programmers won’t become an expert on each implementation of each extension • Extension pragmatics are not documented Navrátil - UT Austin

  3. Current Compilers Are Dumb • Current compilers understand only syntax • Incorrect use of library abstractions are allowed float * vtx = func_023(200*func_041(float)); func_174(2, 0x1406, 0, vtx); func_288(0x8074); func_075(vtx); GLfloat *vtx = malloc(200*sizeof(GLfloat)); glVertexPointer(2, GL_FLOAT, 0, vtx); glEnableClientState(GL_VERTEX_ARRAY); free(vtx); GLfloat *vtx = glXAllocateMemoryNV(200*sizeof(GLfloat),0.0,0.0,1.0); glVertexPointer(2, GL_FLOAT, 0, vtx); glEnableClientState(GL_VERTEX_ARRAY_RANGE_NV); glEnableClientState(GL_VERTEX_ARRAY); glXFreeMemoryNV(vtx); [Adapted from Sam Guyer] Navrátil - UT Austin

  4. Solution: Library Annotations • Expert annotates extension definition • Makes programmer knowledge explicit • Relationships among functions (e.g. malloc and free) • Function arguments, e.g.: glBegin(…), glEnable(…) • Specializations, e.g.: GL_VERTEX_ARRAY, GL_VERTEX_ARRAY_RANGE_NV • Compiler applies expert knowledge to user code • Effort amortized across use of library • Need a complete system to perform all opts Navrátil - UT Austin

  5. System: Broadway [Guyer, Lin; 2000, 2003] [Guyer 2003] • Library meta-interface to describe: • Domain-specific analysis • Domain-specific transformations • Client-driven: adaptive analysis strength • [ Flow | Context ] [ Insensitive | Sensitive ] • Provides powerful analysis at cheap cost • Pointer analysis important too • Need accurate picture of memory Navrátil - UT Austin

  6. Example: Vertex Arrays %{ // Mesa GL types #include "pnav_enum.h" #include <malloc.h> /* these OpenGL functions use vertex and color arrays */ void glVertexPointer( int size, int type, int stride, int ptr ); void glColorPointer( int size, int type, int stride, int ptr ); void glTexCoordPointer( int size, int type, int stride, int ptr ); /* this is called to enable the use of the arrays */ /* vals are GL_VERTEX_ARRAY, GL_COLOR_ARRAY, GL_TEXTURE_COORD_ARRAY */ void glEnableClientState( int type ); }% property MemoryType : { Normal, Vector, Color, Texture } initially Normal Navrátil - UT Austin

  7. Example: Vertex Arrays procedure glVertexPointer( size, type, stride, ptr ) { on_entry { ptr --> memory_chunk } analyze MemoryType { memory_chunk <- Vector } when (1==1) replace with %{ { glVertexArrayRangeNV( ${size}, ${ptr} ); glVertexPointer( ${size}, ${type}, ${stride}, ${ptr} ); } }% } procedure glEnableClientState( type ) { when (type == GL_VERTEX_ARRAY) replace-with %{ { glEnableClientState(GL_VERTEX_ARRAY_RANGE_NV); glEnableClientState(GL_VERTEX_ARRAY); } }% } Navrátil - UT Austin

  8. Example: Vertex Arrays procedure malloc( size ) { on_exit { return --> new memory_chunk } modify { memory_chunk } when (MemoryType : memory_chunk is-exactly Vector || replace-with %{ glAllocateMemoryNV(${size}, 0.0, 0.0, 0.75); }% } procedure free( ptr ) { on_entry { ptr --> memory_chunk } modify { memory_chunk } when (MemoryType : memory_chunk is-exactly Vector) replace-with %{ glXFreeMemoryNV( ${ptr} ); }% } Navrátil - UT Austin

  9. Initial Results: gfxbench • Adaptation of class project code [Ian Buck] • Originally designed to test rasterization pattern • Triangle strip: 100 triangles, 202 vertices • Strip rotated 360º in 5º increments • Strip repeatedly rendered for one second of clock time per orientation (~ 3 sec) Navrátil - UT Austin

  10. Initial Results: gfxbench Navrátil - UT Austin

  11. Issues: gfxbench and beyond • Is the extension used correctly? • Are vertices getting flushed prematurely? • Is the vertex declaration in the right place to capitalize on the benefits of the extension? • GLUT windowing callback structure • Broadway’s analysis cannot reach into function specified by glutDisplayFunc() • Annotation of glutMainLoop() may fix this • Do we even need Broadway? • Implemented gfxbench optimization in perl • More complex programs will need pointer analysis • How many others can be inserted automatically? Navrátil - UT Austin

  12. Future Work • More complex models • Tessellated spheres – 13k, 130k triangles • Texture mapped surfaces • Suggest opportunities to use subjective extensions • Expand to errors • OpenGL • Matching glBegin(), glEnd() pairs • Invalid command between glBegin(), glEnd() • Windowing libraries (GLUT, X, MFC) • No glutPostRedisplay() call in function marked with glutReshapeFunc() • glutKeyboardFunc() vs. glutSpecialFunc() Navrátil - UT Austin

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