Adds a third init function to the store testdata: an initial partial
store puts the buffer into the current memory view, then a partial load
is followed by another partial store at the same offset, and finally the
loaded value is written to a separate global.
The expected output captures the current (incorrect) behavior of the
in-place partial store optimization: the loaded value gets corrupted by
the subsequent in-place store. The next commit fixes this.
memoryView.store cloned the entire destination object on every partial
store. Compiling a program that pulls in golang.org/x/text/collate hit
this hard: its generated tables are initialized one element at a time,
and each element store copied the whole global, making interp quadratic
in the table size.
Switch to copy-on-first-write per memory view: clone the object the
first time this view writes to it, then mutate that private copy in
place on later partial stores. Rollback is unaffected because revert
still discards the view's objects wholesale.
Two extra safety tweaks fall out of this:
- Full overwrites now clone the incoming value, so the stored buffer
can never alias state held by the caller.
- Partial in-place stores snapshot the source buffer, so a store
whose source is a load from the same object (overlapping or not)
still sees the pre-store bytes.
Add an interp golden test exercising both the overlapping load/store
case and a cross-object aliased load/store case.
Jake Bailey