For a full explanation, see interp/README.md. In short, this rewrite is
a redesign of the partial evaluator which improves it over the previous
partial evaluator. The main functional difference is that when
interpreting a function, the interpretation can be rolled back when an
unsupported instruction is encountered (for example, an actual unknown
instruction or a branch on a value that's only known at runtime). This
also means that it is no longer necessary to scan functions to see
whether they can be interpreted: instead, this package now just tries to
interpret it and reverts when it can't go further.
This new design has several benefits:
* Most errors coming from the interp package are avoided, as it can
simply skip the code it can't handle. This has long been an issue.
* The memory model has been improved, which means some packages now
pass all tests that previously didn't pass them.
* Because of a better design, it is in fact a bit faster than the
previous version.
This means the following packages now pass tests with `tinygo test`:
* hash/adler32: previously it would hang in an infinite loop
* math/cmplx: previously it resulted in errors
This also means that the math/big package can be imported. It would
previously fail with a "interp: branch on a non-constant" error.
This commit replaces most panics in interp/frame.go and interp/scan.go
with real error messages. The remaining ones are panics that should not
happen when working with valid IR.
This commit improves error reporting in several ways:
* Location information is read from the intruction that causes the
error, as far as that's available.
* The package that is being interpreted is included in the error
message. This may be the most useful part of the improvements.
* The hashmap update intrinsics now doesn't panic, instead it logs a
clear error (with location information, as in the above two bullet
points).
This is possible thanks to improvements in LLVM 9. This means that after
this change, TinyGo will depend on LLVM 9.
This interpreter currently complements the Go SSA level interpreter. It
may stay complementary or may be the only interpreter in the future.
This interpreter is experimental and not yet finished (there are known
bugs!) so it is disabled by default. It can be enabled by passing the
-initinterp flag.
The goal is to be able to run all initializations at compile time except
for the ones having side effects. This mostly works except perhaps for a
few edge cases.
In the future, this interpeter may be used to actually run regular Go
code, perhaps in a shell.
