This key was intended as some sort of cache key (as the name indicates)
but that never happened. Let's remove it to avoid clutter. The cacheLoad
and cacheStore functions are only used for C libraries (libc,
compiler-rt) so their caching behavior is a bit different from other
things worth caching.
This commit parallelizes almost everything that can currently be
parallelized. With that, it also introduces a framework for easily
parallelizing other parts of the compiler.
Code for baremetal targets already compiles slightly faster because it
can parallelize the compilation of supporting assembly files. However,
the speedup is especially noticeable when libraries (compiler-rt,
picolibc) also need to be compiled: they will be compiled in parallel
next to the Go files using all available cores. On my dual core laptop
(4 cores if you count hyperthreading) this cuts compilation time roughly
in half when compiling something for a Cortex-M board after running
`tinygo clean`.
This is a large commit that moves all code directly related to
compiling/linking into a new builder package. This has a number of
advantages:
* It cleanly separates the API between the command line and the full
compilation (with a very small API surface).
* When the compiler finally compiles one package at a time (instead of
everything at once as it does now), something will have to invoke it
once per package. This builder package will be the natural place to
do that, and also be the place where the whole process can be
parallelized.
* It allows the TinyGo compiler to be used as a package. A client can
simply import the builder package and compile code using it.
As part of this refactor, the following additional things changed:
* Exported symbols have been made unexported when they weren't needed.
* The compilation target has been moved into the compileopts.Options
struct. This is done because the target really is just another
compiler option, and the API is simplified by moving it in there.
* The moveFile function has been duplicated. It does not really belong
in the builder API but is used both by the builder and the command
line. Moving it into a separate package didn't seem useful either
for what is essentially an utility function.
* Some doc strings have been improved.
Some future changes/refactors I'd like to make after this commit:
* Clean up the API between the builder and the compiler package.
* Perhaps move the test files (in testdata/) into the builder package.
* Perhaps move the loader package into the builder package.
