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vii
Considerations for Code Conversion to SIMD Programming.................................................. 3-8
Identifying Hot Spots ...................................................................................................... 3-10
Determine If Code Benefits by Conversion to SIMD Execution...................................... 3-11
Coding Techniques ............................................................................................................... 3-12
Coding Methodologies.................................................................................................... 3-13
Assembly.................................................................................................................. 3-15
Intrinsics.................................................................................................................... 3-15
Classes..................................................................................................................... 3-17
Automatic Vectorization............................................................................................ 3-18
Stack and Data Alignment..................................................................................................... 3-20
Alignment and Contiguity of Data Access Patterns........................................................ 3-20
Using Padding to Align Data..................................................................................... 3-20
Using Arrays to Make Data Contiguous.................................................................... 3-21
Stack Alignment For 128-bit SIMD Technologies ........................................................... 3-22
Data Alignment for MMX Technology ............................................................................. 3-23
Data Alignment for 128-bit data...................................................................................... 3-24
Compiler-Supported Alignment................................................................................. 3-24
Improving Memory Utilization................................................................................................ 3-27
Data Structure Layout..................................................................................................... 3-27
Strip Mining..................................................................................................................... 3-32
Loop Blocking................................................................................................................. 3-34
Instruction Selection.............................................................................................................. 3-37
SIMD Optimizations and Microarchitectures .................................................................. 3-38
Tuning the Final Application.................................................................................................. 3-39
Chapter 4 Optimizing for SIMD Integer Applications
General Rules on SIMD Integer Code .................................................................................... 4-2
Using SIMD Integer with x87 Floating-point............................................................................ 4-3
Using the EMMS Instruction............................................................................................. 4-3
Guidelines for Using EMMS Instruction............................................................................ 4-4
Data Alignment........................................................................................................................ 4-6
Data Movement Coding Techniques ....................................................................................... 4-6
Unsigned Unpack............................................................................................................. 4-6
Signed Unpack................................................................................................................. 4-7
Interleaved Pack with Saturation...................................................................................... 4-8
Interleaved Pack without Saturation............................................................................... 4-10
Non-Interleaved Unpack................................................................................................. 4-11
Extract Word................................................................................................................... 4-13
Insert Word..................................................................................................................... 4-14
Move Byte Mask to Integer............................................................................................. 4-16