CompilerAssisted Optimization for Graphics

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Compiler-Assisted Optimization for Graphics

• Paul Arthur Navrátil
• The University of Texas at Austin

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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 wont become an expert on each
  implementation of each extension
• Extension pragmatics are not documented

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Current Compilers Are Dumb

• Current compilers understand only syntax
• Incorrect use of library abstractions are allowed

float vtx func_023(200func_041(float)) func_
174(2, 0x1406, 0, vtx) func_288(0x8074) func_07
5(vtx)
GLfloat vtx malloc(200sizeof(GLfloat)) glVert
exPointer(2, GL_FLOAT, 0, vtx) glEnableClientSta
te(GL_VERTEX_ARRAY) free(vtx)
GLfloat vtx glXAllocateMemoryNV(200sizeof(GLfl
oat),0.0,0.0,1.0) glVertexPointer(2, GL_FLOAT,
0, vtx) glEnableClientState(GL_VERTEX_ARRAY_RANGE
_NV) glEnableClientState(GL_VERTEX_ARRAY) glXFre
eMemoryNV(vtx)
Adapted from Sam Guyer
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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

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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

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Example Vertex Arrays

• // Mesa GL types
• include "pnav_enum.h"
• include ltmalloc.hgt
• / 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

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Example Vertex Arrays

• procedure glVertexPointer( size, type, stride,
  ptr )
• on_entry ptr --gt memory_chunk
• analyze MemoryType memory_chunk lt- Vector
• when (11) 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)

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Example Vertex Arrays

• procedure malloc( size )
• on_exit return --gt 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 --gt memory_chunk
• modify memory_chunk
• when (MemoryType memory_chunk is-exactly
  Vector)
• replace-with glXFreeMemoryNV( ptr )

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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)

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Initial Results gfxbench
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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
• Broadways 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?

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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()