Emergency stack slots are a new kind of stack slot added relatively
recently. They need to be allocated a stack offset just like explicit
and spill slots.
Also, make StackSlotData's offset field an Option, to catch problems
like this in the future. Previously the value 0 was used when offsets
weren't assigned yet, however that made it non-obvious when the field
meant "not assigned yet" and when it meant "assigned the value 0".
Spiderwasm on 32-bit x86 always uses a 16-byte-aligned stack pointer.
Change the setting for the "native" convention as well, for
compatibility with Linux and Darwin ABIs, and so that if a platform
has different ABI rules, the problem will be detected in code emitted by
Cretonne, rather than somewhere else.
The term "local variables" predated the SSA builder in the front-end
crate, which also provides a way to implement source-language local
variables. The name "explicit stack slot" makes it clear what this
construct is.
Adds support for transforming integer division and remainder by constants
into sequences that do not involve division instructions.
* div/rem by constant powers of two are turned into right shifts, plus some
fixups for the signed cases.
* div/rem by constant non-powers of two are turned into double length
multiplies by a magic constant, plus some fixups involving shifts,
addition and subtraction, that depends on the constant, the word size and
the signedness involved.
* The following cases are transformed: div and rem, signed or unsigned, 32
or 64 bit. The only un-transformed cases are: unsigned div and rem by
zero, signed div and rem by zero or -1.
* This is all incorporated within a new transformation pass, "preopt", in
lib/cretonne/src/preopt.rs.
* In preopt.rs, fn do_preopt() is the main driver. It is designed to be
extensible to transformations of other kinds of instructions. Currently
it merely uses a helper to identify div/rem transformation candidates and
another helper to perform the transformation.
* In preopt.rs, fn get_div_info() pattern matches to find candidates, both
cases where the second arg is an immediate, and cases where the second
arg is an identifier bound to an immediate at its definition point.
* In preopt.rs, fn do_divrem_transformation() does the heavy lifting of the
transformation proper. It in turn uses magic{S,U}{32,64} to calculate the
magic numbers required for the transformations.
* There are many test cases for the transformation proper:
filetests/preopt/div_by_const_non_power_of_2.cton
filetests/preopt/div_by_const_power_of_2.cton
filetests/preopt/rem_by_const_non_power_of_2.cton
filetests/preopt/rem_by_const_power_of_2.cton
filetests/preopt/div_by_const_indirect.cton
preopt.rs also contains a set of tests for magic number generation.
* The main (non-power-of-2) transformation requires instructions that return
the high word of a double-length multiply. For this, instructions umulhi
and smulhi have been added to the core instruction set. These will map
directly to single instructions on most non-intel targets.
* intel does not have an instruction exactly like that. For intel,
instructions x86_umulx and x86_smulx have been added. These map to real
instructions and return both result words. The intel legaliser will
rewrite {s,u}mulhi into x86_{s,u}mulx uses that throw away the lower half
word. Tests:
filetests/isa/intel/legalize-mulhi.cton (new file)
filetests/isa/intel/binary64.cton (added x86_{s,u}mulx encoding tests)
Maintain an explicit "reachable" flag when decoding wasm. Push placeholder
frames on the control-flow stack instead of just maintaining a count of
the stack depth in unreachable code, so that we can whether If blocks
have Elses, and whether block exits are branched to, in all contexts.
Fixes#217.
With the change to the parser to preserve indices, it now inserts
placeholders to pad out index spaces as needed. Placeholder functions
use reserved signature indices, so skip them when writing them out,
to avoid writing them out as "sig4294967295".
Cretonne clients don't need to know how the register allocator works.
Export the RegDiversions type from the binemit module instead. It is
used by the "test binemit" driver.
StackSlotKind::OutgoingArg stack slots have an offset that is relative
to our own stack pointer, while all other stack slot kinds have offsets
that are relative to the caller's stack pointer.
Make sure we generate the right sp-relative offsets for outgoing
arguments too.
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.
