Re: Compile-time v. execution-time tradeoff

On Tue, Feb 16, 2016 at 8:49 AM, Rob Arthan <[email protected]> wrote:
> Does MLton have any options that let me trade off execution time against compile time? The scenario is that I have a parser generator that I have recently ported to run on MLton. The parser generator itself is very efficient when built with MLton, but the test suite runs slowly because of the time taken to compile the generated parsers. As the tests only run each parser once, it would be nice if I could speed up the tests by opting for less optimisation. I tried -inline 0, but it didn’t make much difference.

MLton doesn't currently have distinct optimization levels.  The
"-drop-pass" option can be used to skip a particular optimization
pass.  The "-ssa-passes" option (and similarly for the other IRs) can
be used to set a particular sequence of optimization passes;
"-ssa-passes minimal" is recognized and will only execute those passes
necessary for correctness.  Unfortunately, while this speeds up the
time in the SSA optimizations, it tends to slow down the codegen
significantly, since the program hasn't be simplified.

There is also a minimum of time that any compile takes, due to the
whole-program compilation requiring scanning, parsing, and elaborating
the whole Basis Library in addition to the program of interest.

You could try compiling one of your representative tests with
"-verbose 2", which will give timings for all of the optimization
passes.  If a particular pass is taking very long, then you can use
"-drop-pass" to skip that one.  Occasionally, performance bugs in the
optimization passes have turned up, especially when presented with
stylistically distinct code, such as might appear in parser generator
output.

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