Programming Languages explained (funny pic)

[Kosmik]

Pity they did not include assembler, and that old stalwart, BASIC...

10 PRINT "RESCUE THE PRINCESS"
20 GOTO CASTLE
30 GOTO PRINCESS
40 GOTO END

Please correct line 40 as per std 80's spec

40 PRINT "PRINCESS HAS BEEN TAKEN AGAIN"
50 GOTO 10

 

[mercurial]

I typically write this type of code in C or C++ and compile it. I will then use something like objdump or a compilation with the -S option to see the assembler source code that was generated. I will then look at the assembler and see if there are any inefficiencies in the code that was generated.

The kind of thing I would look for may be:
- Short pieces of code not being inlined
- The compiler can't tell that there is no overwrite between two reads of a global variable, so it gets read every time
- The compiler runs out of registers within a loop, and spill to the the stack
- The compiler generates many jumps to early out of a compound condition that I will almost always be true
- The compiler may make incorrect assumptions about the likelihood of a condition being true or false
- The compiler may correctly choose the likelihood of a condition being true or false, however, the unlikely case may be the speed sensitive one (and the one I want the CPU speculate)
- Compares and jumps can perhaps be avoided by conditional moves
- Vectorization may have unintended side effects
- Hand vectorization may accelerate a given piece of code
- The compiler may not be able to make assumptions about loop variable sizes, so it generates unnecessary remainder handling code that bloats the code cache as it gets prefetched.
- etc.

Wow, that's quite interesting, thanks

 

[Compton_effect]

You have VB6. You find a magic sword that rescues the princess for you - written ages ago by a wise and ancient programmer., You have no idea how it works and no way to find out, but no-one will notice if you use it. Everything is great, but now they want you to rescue a prince instead.

 

[cguy]

Wow, that's quite interesting, thanks

Sure.

BTW, today I needed to decompile some code to see why some hand vectorized code was slower than scalar code.

 

[mercurial]

Sure.

BTW, today I needed to decompile some code to see why some hand vectorized code was slower than scalar code.

You should start a channel on YouTube.

 

[Batista]

Thats why I love C# !

 

[cguy]

You should start a channel on YouTube.

Heh - tempting, but not sure what my employer would think of it.

 

[Nefertiti]

You have VB6. You find a magic sword that rescues the princess for you - written ages ago by a wise and ancient programmer., You have no idea how it works and no way to find out, but no-one will notice if you use it. Everything is great, but now they want you to rescue a prince instead.

you owe me a cup of coffee :crylaugh: