Mark loads from globals generated by cton_wasm or by legalization as
`aligned` and `notrap`, since memory for these globals should be
allocated by the runtime environment for that purpose. This reduces
the number of potentially trapping instructions, which can reduce
the amount of metadata required by embedding environments.
This makes it easier to debug testcases:
- the entity numbers in a .cton file match the entity numbers used
within Cretonne.
- serializing and deserializing doesn't cause indices to change.
One disadvantage is that if a .cton file uses sparse entity numbers,
deserializing to the in-memory form doesn't compact it. However, the
text format is not intended to be performance-critical, so this isn't
expected to be a big burden.
This instruction loads a stack limit from a global variable and compares
it to the stack pointer, trapping if the stack has grown beyond the
limit.
Also add a expand_flags transform group containing legalization patterns
for ISAs with CPU flags.
Fixes#234.
The expansion of a heap_addr instruction depends on the type of heap and
its configuration, so this is handled by custom code.
Add a couple examples of heap access code to the language reference
manual.
The code to compute the address of a global variable depends on the kind
of variable, so custom legalization is required.
- Add a legalizer::globalvar module which exposes an
expand_global_addr() function. This module is likely to grow as we add
more types of global variables.
- Add a ArgumentPurpose::VMContext enumerator. This is used to represent
special 'vmctx' arguments that are used as base pointers for vmctx
globals.
