inside the GHC code generator

Kevin Glynn glynn at
Thu Feb 23 13:06:25 EST 2006

Claus Reinke writes:
 > > the long answer is: are you ever heard promises that gcc is best
 > > cpu-independent assembler? no? and you know why? because gcc is not
 > > cpu-independent assembler. gcc was strongly optimized to make
 > > efficient asm from the code usually written by the C programmers. but
 > > code generated by ghc has nothing common with it. so we are stay with
 > > all these register-memory moves, non-unrolled loops and all other
 > > results of naive compilation. gcc is just don't know how to
 > > efficiently manage such code!
 > would there be any advantage to targetting gcc's backend directly?
 > I notice that Mercury seems to support this:
 > that is, does using C as assembler disable possible optimizations,
 > or is going through the C frontend enabling more optimizations than
 > going to the backend directly?

On a related point, Mercury has two C backends a low level one at the
level of GHC's and a high level one. Bulat might want to read this for
a description of the high level C implementation:

Also, ghc used to be faster than gcc for a naive, recursive factorial
function (once the cpr analysis and optimisation was added).  From
what Bulat wrote it seems that gcc got better ...


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