Make sure all allocas are created in the entry block and are given the
right lifetimes. This is good for code quality:
* Moving allocas to the entry block makes sure they are always
allocated statically (avoiding the need for a frame pointer) and do
not grow the stack on each new alloca instruction. This is
especially useful in loops where it could otherwise lead to a stack
overflow even though there is no recursion.
* Adding lifetime markers allows LLVM to reuse stack areas for
different allocas as long as their lifetimes do not overlap.
All in all, this reduces code size in all tested cases for the BBC
micro:bit, and reduces code size for most cases for WebAssembly.
By moving all allocas used in hashmap operations to the entry block, the
stack frame remains at a fixed size known at compile time. This avoids
stack overflows when doing map operations in loops and in general
improves code quality: the compiled size of testdata/map.go went from
3776 to 3632 in .text size.
Most of these errors are actually "todo" or "unimplemented" errors, so
the return type is known. This means that compilation can proceed (with
errors) even though the output will be incorrect. This is useful because
this way, all errors in a compilation unit can be shown together to the
user.
This commit replaces "unknown type" errors in getLLVMType with panics.
The main reason this is done is that it simplifies the code *a lot*.
Many `if err != nil` lines were there just because of type information.
Additionally, simply panicking is probably a better approach as the only
way this error can be produced is either with big new language features
or a serious compiler bug. Panicking is probably a better way to handle
this error anyway.
Ayke van Laethem
Konstantin Yegupov