1. Rational Apex 4.0 Optimization “Beware the benchmark!”

2. Solid Palette Gradient Palette I Gradient Palette II APPLYING THESE COLORS 1.1. 2.2. 3.3. Click on the desired color Click on the paintbrush tool located on your toolbar Click on the object you want to colorize Helpful tip: Double click the paintbrush tool to apply color to more than one object at a time. Do not use Gradient or transparent fills for slides to be used on PlaceWare.com To use or remove these color palettes, go to View/Master/Slide Master Optional logo for your notes/handouts slides Presentation Outline  Outline Rational Apex optimization behaviour  Demonstrate some of the optimization techniques being used by modern compilers  Show how these techniques defeat many of the assumptions made by traditional benchmarking suites  Outline Rational Apex optimization behaviour  Demonstrate some of the optimization techniques being used by modern compilers  Show how these techniques defeat many of the assumptions made by traditional benchmarking suites

3. Solid Palette Gradient Palette I Gradient Palette II APPLYING THESE COLORS 1.1. 2.2. 3.3. Click on the desired color Click on the paintbrush tool located on your toolbar Click on the object you want to colorize Helpful tip: Double click the paintbrush tool to apply color to more than one object at a time. Do not use Gradient or transparent fills for slides to be used on PlaceWare.com To use or remove these color palettes, go to View/Master/Slide Master Optional logo for your notes/handouts slides Rational Apex Optimization  Optimization with Apex has 3 levels, controlled by the OPTIMIZATION_LEVEL switch  Level 0 – No optimization, maximize debuggability This is the default  Level 1 – Many optimizations performed, some debuggability maintained  Level 2 – All optimizations performed, debugging may be very limited in some code  Optimization with Apex can have one of two objectives  Time – try to generate code with that will execute in minimal time  Space – try to generate code that is as compact as possible  These two objectives are not mutually exclusive!  Optimization with Apex has 3 levels, controlled by the OPTIMIZATION_LEVEL switch  Level 0 – No optimization, maximize debuggability This is the default  Level 1 – Many optimizations performed, some debuggability maintained  Level 2 – All optimizations performed, debugging may be very limited in some code  Optimization with Apex can have one of two objectives  Time – try to generate code with that will execute in minimal time  Space – try to generate code that is as compact as possible  These two objectives are not mutually exclusive!

4. Solid Palette Gradient Palette I Gradient Palette II APPLYING THESE COLORS 1.1. 2.2. 3.3. Click on the desired color Click on the paintbrush tool located on your toolbar Click on the object you want to colorize Helpful tip: Double click the paintbrush tool to apply color to more than one object at a time. Do not use Gradient or transparent fills for slides to be used on PlaceWare.com To use or remove these color palettes, go to View/Master/Slide Master Optional logo for your notes/handouts slides Rational Apex Optimization  Apex performs optimization in several different places  Front End – post semantics Common sub-expression elimination Code in-lining Loop unrolling Remove unused code from local scope  Machine independent instruction stream optimizer “optim” Loop invariant hoisting Range propogation Constraint check elimination Reduce memory movement  Machine specific code generator Peep-hole optimization  All optimization consumes extra CPU during compilation  The default is off – OPTIMIZATION_LEVEL: 0  Apex performs optimization in several different places  Front End – post semantics Common sub-expression elimination Code in-lining Loop unrolling Remove unused code from local scope  Machine independent instruction stream optimizer “optim” Loop invariant hoisting Range propogation Constraint check elimination Reduce memory movement  Machine specific code generator Peep-hole optimization  All optimization consumes extra CPU during compilation  The default is off – OPTIMIZATION_LEVEL: 0

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8. Solid Palette Gradient Palette I Gradient Palette II APPLYING THESE COLORS 1.1. 2.2. 3.3. Click on the desired color Click on the paintbrush tool located on your toolbar Click on the object you want to colorize Helpful tip: Double click the paintbrush tool to apply color to more than one object at a time. Do not use Gradient or transparent fills for slides to be used on PlaceWare.com To use or remove these color palettes, go to View/Master/Slide Master Optional logo for your notes/handouts slides Optimization Level 0  No inlining, no code elimination, no check elimination  Disassembly of sum_sqrt.2.ada is 15845 lines long  No unused code has been eliminated – all the code for generic_elementary_functions remains  No inlining, no code elimination, no check elimination  Disassembly of sum_sqrt.2.ada is 15845 lines long  No unused code has been eliminated – all the code for generic_elementary_functions remains

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10. Solid Palette Gradient Palette I Gradient Palette II APPLYING THESE COLORS 1.1. 2.2. 3.3. Click on the desired color Click on the paintbrush tool located on your toolbar Click on the object you want to colorize Helpful tip: Double click the paintbrush tool to apply color to more than one object at a time. Do not use Gradient or transparent fills for slides to be used on PlaceWare.com To use or remove these color palettes, go to View/Master/Slide Master Optional logo for your notes/handouts slides Optimization Level 0 – Disassembly of sqrt  163 lines of assembly  Slightly abridged  163 lines of assembly  Slightly abridged

11. Solid Palette Gradient Palette I Gradient Palette II APPLYING THESE COLORS 1.1. 2.2. 3.3. Click on the desired color Click on the paintbrush tool located on your toolbar Click on the object you want to colorize Helpful tip: Double click the paintbrush tool to apply color to more than one object at a time. Do not use Gradient or transparent fills for slides to be used on PlaceWare.com To use or remove these color palettes, go to View/Master/Slide Master Optional logo for your notes/handouts slides Optimization Level 0 – Disassembly of hardware  56 Lines of disassembly for SQRT  10 Instructions for SQRT_32  56 Lines of disassembly for SQRT  10 Instructions for SQRT_32

12. Solid Palette Gradient Palette I Gradient Palette II APPLYING THESE COLORS 1.1. 2.2. 3.3. Click on the desired color Click on the paintbrush tool located on your toolbar Click on the object you want to colorize Helpful tip: Double click the paintbrush tool to apply color to more than one object at a time. Do not use Gradient or transparent fills for slides to be used on PlaceWare.com To use or remove these color palettes, go to View/Master/Slide Master Optional logo for your notes/handouts slides Optimization Level 0 – Summary  Total of over 220 instructions generated for the code that we are interested in  Lots of it will be unused  Not to mention the rest of the code for the instantiation  Code maps back to source easily  Code layout follows source  Lots of overhead for this straightforward code  Subprogram prolog/epilog code Stack checks Register management  Subprogram call/return code (3 levels deep)  No delayed branch slots being filled  Total of over 220 instructions generated for the code that we are interested in  Lots of it will be unused  Not to mention the rest of the code for the instantiation  Code maps back to source easily  Code layout follows source  Lots of overhead for this straightforward code  Subprogram prolog/epilog code Stack checks Register management  Subprogram call/return code (3 levels deep)  No delayed branch slots being filled

13. Solid Palette Gradient Palette I Gradient Palette II APPLYING THESE COLORS 1.1. 2.2. 3.3. Click on the desired color Click on the paintbrush tool located on your toolbar Click on the object you want to colorize Helpful tip: Double click the paintbrush tool to apply color to more than one object at a time. Do not use Gradient or transparent fills for slides to be used on PlaceWare.com To use or remove these color palettes, go to View/Master/Slide Master Optional logo for your notes/handouts slides Optimization Level 2 – Disassembly of “for” loop

14. Solid Palette Gradient Palette I Gradient Palette II APPLYING THESE COLORS 1.1. 2.2. 3.3. Click on the desired color Click on the paintbrush tool located on your toolbar Click on the object you want to colorize Helpful tip: Double click the paintbrush tool to apply color to more than one object at a time. Do not use Gradient or transparent fills for slides to be used on PlaceWare.com To use or remove these color palettes, go to View/Master/Slide Master Optional logo for your notes/handouts slides Optimization Level 2 – Observations  Disassembly of sum_sqrt.2.ada is 85 lines long  Entire loop and all the called subprogram code is now 12 instructions long  5 instructions for “for” loop management Includes 2 instructions for branching  4 instructions for integer to float conversion 2 are identical, as one copy is used to fill a delayed branch slot at the bottom of the loop  1 instruction for the Text_Io code is used to fill a branch delay slot  2 Instructions to perform the actual Sqrt and summation.  Disassembly of sum_sqrt.2.ada is 85 lines long  Entire loop and all the called subprogram code is now 12 instructions long  5 instructions for “for” loop management Includes 2 instructions for branching  4 instructions for integer to float conversion 2 are identical, as one copy is used to fill a delayed branch slot at the bottom of the loop  1 instruction for the Text_Io code is used to fill a branch delay slot  2 Instructions to perform the actual Sqrt and summation.

15. Solid Palette Gradient Palette I Gradient Palette II APPLYING THESE COLORS 1.1. 2.2. 3.3. Click on the desired color Click on the paintbrush tool located on your toolbar Click on the object you want to colorize Helpful tip: Double click the paintbrush tool to apply color to more than one object at a time. Do not use Gradient or transparent fills for slides to be used on PlaceWare.com To use or remove these color palettes, go to View/Master/Slide Master Optional logo for your notes/handouts slides Optimization Level 2 – Observations  The optimization objective was Time  Time is certainly optimized, but Space also benefited enormously  Different optimization techniques combined effectively to produce very effective code  Inlining of 3 levels of subprogram call eliminated a significant amount of subprogram prolog/epilog  Range propagation determined that the argument to SQRT could never be less than zero, which allowed the argument check to be removed  Evaluation of compile static expressions resulted in a lot of code not being generated Kind of floating point type – no case statement needed Availability of Hardware SQRT – no call needed to Has_Sqrt  Register lifetime analysis on the resulting code meant that the loop control variable and the summation variable could live in registers  The optimization objective was Time  Time is certainly optimized, but Space also benefited enormously  Different optimization techniques combined effectively to produce very effective code  Inlining of 3 levels of subprogram call eliminated a significant amount of subprogram prolog/epilog  Range propagation determined that the argument to SQRT could never be less than zero, which allowed the argument check to be removed  Evaluation of compile static expressions resulted in a lot of code not being generated Kind of floating point type – no case statement needed Availability of Hardware SQRT – no call needed to Has_Sqrt  Register lifetime analysis on the resulting code meant that the loop control variable and the summation variable could live in registers

16. Solid Palette Gradient Palette I Gradient Palette II APPLYING THESE COLORS 1.1. 2.2. 3.3. Click on the desired color Click on the paintbrush tool located on your toolbar Click on the object you want to colorize Helpful tip: Double click the paintbrush tool to apply color to more than one object at a time. Do not use Gradient or transparent fills for slides to be used on PlaceWare.com To use or remove these color palettes, go to View/Master/Slide Master Optional logo for your notes/handouts slides Performing Benchmarks  Benchmarks usually consist of two distinct loops  A “Null Timing” loop to determine the overhead of the loop code itself  The Code Under Test loop which has the same structure as the Null timing loop with the inside of the loop replaced with the C.U.T  Timing equation looks like  T CUT = (T CUT_loop – T null_loop ) / n Where n is the number of iterations Usually n has to be very high so that the resolution of the system clock is not significant in the result  Benchmarks usually consist of two distinct loops  A “Null Timing” loop to determine the overhead of the loop code itself  The Code Under Test loop which has the same structure as the Null timing loop with the inside of the loop replaced with the C.U.T  Timing equation looks like  T CUT = (T CUT_loop – T null_loop ) / n Where n is the number of iterations Usually n has to be very high so that the resolution of the system clock is not significant in the result

17. Solid Palette Gradient Palette I Gradient Palette II APPLYING THESE COLORS 1.1. 2.2. 3.3. Click on the desired color Click on the paintbrush tool located on your toolbar Click on the object you want to colorize Helpful tip: Double click the paintbrush tool to apply color to more than one object at a time. Do not use Gradient or transparent fills for slides to be used on PlaceWare.com To use or remove these color palettes, go to View/Master/Slide Master Optional logo for your notes/handouts slides Performing Benchmarks  One effect we notice is that sometimes a benchmark suite reports slower times for code even though we know we have improved our optimizations!  What’s happening?  The Null Timing loops of benchmark suites attempt to defeat compiler optimizations that skew their results  Compilers are better at getting rid of unnecessary code, often defeating the smart null loop  So now the equation looks like: T CUT = (T CUT_loop – 0 ) / n  So the remaining loop overhead time gets included in the time of the Code Under Test making it look worse than before  One effect we notice is that sometimes a benchmark suite reports slower times for code even though we know we have improved our optimizations!  What’s happening?  The Null Timing loops of benchmark suites attempt to defeat compiler optimizations that skew their results  Compilers are better at getting rid of unnecessary code, often defeating the smart null loop  So now the equation looks like: T CUT = (T CUT_loop – 0 ) / n  So the remaining loop overhead time gets included in the time of the Code Under Test making it look worse than before

18. Solid Palette Gradient Palette I Gradient Palette II APPLYING THESE COLORS 1.1. 2.2. 3.3. Click on the desired color Click on the paintbrush tool located on your toolbar Click on the object you want to colorize Helpful tip: Double click the paintbrush tool to apply color to more than one object at a time. Do not use Gradient or transparent fills for slides to be used on PlaceWare.com To use or remove these color palettes, go to View/Master/Slide Master Optional logo for your notes/handouts slides Performing Benchmarks  One other effect we observe is that benchmarks often don’t do anything with the results they calculate  Compilers can detect this and conclude that running the code has no effect and (very importantly) no side-effects  Range propagation concludes that overflow cannot be raised  Result is never used  Code is thrown away  A good example is the Henessey Benchmark in the PIWG suite  Large matrix multiplications, using a range of values that will not result in overflow  Apex 4.0 reports zero time for that test  One other effect we observe is that benchmarks often don’t do anything with the results they calculate  Compilers can detect this and conclude that running the code has no effect and (very importantly) no side-effects  Range propagation concludes that overflow cannot be raised  Result is never used  Code is thrown away  A good example is the Henessey Benchmark in the PIWG suite  Large matrix multiplications, using a range of values that will not result in overflow  Apex 4.0 reports zero time for that test

19. Solid Palette Gradient Palette I Gradient Palette II APPLYING THESE COLORS 1.1. 2.2. 3.3. Click on the desired color Click on the paintbrush tool located on your toolbar Click on the object you want to colorize Helpful tip: Double click the paintbrush tool to apply color to more than one object at a time. Do not use Gradient or transparent fills for slides to be used on PlaceWare.com To use or remove these color palettes, go to View/Master/Slide Master Optional logo for your notes/handouts slides Performing Benchmarks  When trying to compare different compiler technologies you need to look beyond the results printed by a benchmark program  Printed numbers can be very misleading  Look at absolute times and iteration counts  Benchmarks don’t translate well b/n processor variants and processor types  The best benchmark is your application  Or a sizable portion of it  When trying to compare different compiler technologies you need to look beyond the results printed by a benchmark program  Printed numbers can be very misleading  Look at absolute times and iteration counts  Benchmarks don’t translate well b/n processor variants and processor types  The best benchmark is your application  Or a sizable portion of it