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High Performance GraphicOn The CPU Using ispc

Matt Pharr

Intel

Beyond Programmable Shading Cours

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Beyond Programmable Shading Cours

ispc: Goals

Deliver excellent performance to programmers

want to run SPMD programs on the CPU

Provide a thin abstraction layer: programmer c

cleanly reason about what the compiler will do

Allow close-coupling and fine-grained interactiobetween C/C++ code and ispc code

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ispc: Key Features

C-based syntax

Pointers, data structures shared with C/C++ code

(no driver/data reformatting)

Only a function call boundary between C/C++ and is

Recursion, externally-defined functions just work

Rich standard library: vectorized transcendentals, a

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Building Applications with ispc

ispc SourceC/C++ Source

ispc Compiler C/C++ Compiler

Object File Object File

Linker

ispc Source C/C++ Source

Executable

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Hello ispcHello ispc

int nVertices = ...;float *x = new float[nVertices];

float *y = new float[nVertices];

float *z = new float[nVertices];

// fill in x[], y[], z[]

float matrix[3][3] = { { ... }, ... };

transform3x3(x, y, z, matrix, nVertices);

export void

transform3x3(uniform float xarray[], uni

uniform float zarray[], uni

uniform int nVertices) {

uniform int i;

for (i = 0; i < nVertices; i +=prog

float x = xarray[i +programInde

float y = yarray[i +programInde

float z = zarray[i +programInde

float xt = m[0][0]*x + m[0][1]*y

float yt = m[1][0]*x + m[1][1]*y

float zt = m[2][0]*x + m[2][1]*y

xarray[i +programIndex] = xt;

yarray[i +programIndex] = yt;

zarray[i +programIndex] = zt;

}

}

ispc CodeC++ Application Code

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A Ray Tracer in ispc

int width = ..., height = ...;

const float raster2camera[4][4] = { ... };const float camera2world[4][4] = { ... };

float *image = new float[width*height];

Triangle *triangles = new Triangle[nTris];

LinearBVHNode *nodes = new LinearBVHNode[nNodes];

// init triangles and nodes

raytrace(width, height, raster2camera,

camera2world, image, nodes, triangles);

export voidraytrace(uniform int width, uniform in

const uniform float raster2ca

const uniform float camera2wo

uniform float image[],

const LinearBVHNode nodes[],

const Triangle triangles[])

// ...

// map program instances to rays

// ...

for (y = 0; y < height; y += yStep

for (x = 0; x < width; x += xS

Ray ray;

generateRay(raster2camera

x+dx, y+dy, ra

BVHIntersect(nodes, triangl

int offset = (y + idy) * wi

image[offset] = ray.maxt;

id[offset] = ray.hitId;

}

}

}

ispc CodC++ Application Code

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PerformanceDual Xeon X5680 (12 cores)

Serial C

ispc

SPMD +tasks

Ray Tracer 1x 102.25x

SHRadiance

Probe Gen.

1x 65.71x

Deferred

Shading1x 39.40x

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Integration WithRegular Debuggers

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Try It Yourself!

ispc is available in open-source from

http://ispc.github.com

Codegen uses the (excellent) LLVM compiler

Supports Linux, Windows, Mac OS X

x86 and x86-64 targets, SSE2 and SSE4

(AVX soon)

http://ispc.github.com/http://ispc.github.com/