This simplifies the process of constructing and encoding layout bitmaps.
Instead of creating big integers and merging them, we can create a pre-sized bitmap and set positions within it.
This also changes the encoding logic to allow larger layouts to be encoded inline.
We would previously not encode a layout inline unless the size was less than the width of the data field.
This is overly conservative.
A layout can be encoded inline as long as:
1. The size fits within the size field.
2. All set bits in the bitmap fit into the data field.
Large object layouts don't fit in a pointer-sized integer and therefore
need to be stored in a global instead. However, the way the data was
stored in these globals was not correct for buffers that don't have
pointers near the end. This commit fixes this issue by using math/big
FillBytes() instead of Bytes().
This gets the unicode package to compile on AVR.
This commit adds object layout information to new heap allocations. It
is not yet used anywhere: the next commit will make use of it.
Object layout information will eventually be used for a (mostly) precise
garbage collector. This is what the data is made for. However, it is
also useful in the interp package which can work better if it knows the
memory layout and thus the approximate LLVM type of heap-allocated
objects.
Nia Waldvogel
Ayke van Laethem