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.
Stop passing Cursor references to legalizer functions. Give them the
whole &mut Function instead. Given the whole Function reference, these
functions can create their own cursors.
This lets legalizer actions access other Function data structures like
the global variables.
The Cursor navigation methods all just depend on the cursor's position
and layout reference. Make a CursorBase trait that provides access to
this information with methods and implement the navigation methods on
top of that.
This makes it possible to have multiple types implement the cursor
interface.
When making an outgoing call, some arguments may have to be passed on
the stack. Allocate OutgoingArg stack slots for these arguments and
write them immediately before the outgoing call instruction.
Do the same for incoming function arguments on the stack, but use
IncomingArg stack slots instead. This was previously done in the
spiller, but we move it to the legalizer so it is done at the same time
as outgoing stack arguments.
These stack slot assignments are done in the legalizer before live
range analysis because the outgoing arguments usually are in different
SSSA values with their own short live ranges.
Replace the isa::Legalize enumeration with a function pointer. This
allows an ISA to define its own specific legalization actions instead of
relying on the default two.
Generate a LEGALIZE_ACTIONS table for each ISA which contains
legalization function pointers indexed by the legalization codes that
are already in the encoding tables. Include this table in
isa/*/enc_tables.rs.
Give the `Encodings` iterator a reference to the action table and change
its `legalize()` method to return a function pointer instead of an
ISA-specific code.
The Result<> returned from TargetIsa::encode() no longer implements
Debug, so eliminate uses of unwrap and expect on that type.
Switch to the new domtree.cfg_postorder() which returns a reference to a
pre-computed post-order instead of allocating memory and computing a new
post-order.
If we generated new instructions as part of legalize, and the new
instructions failed to legalize, we'd be left with a func.encodings[]
that would panic when you dereferenced the inst.
The other legalizer cases have a continue after setting the position
to double back, while this one didn't. Make sure that we do, in case
another legalizer block is added after this one.
These special-purpose arguments and return values are only relevant for
the function being compiled, so add a `current` flag to
legalize_signature().
- Add the necessary argument values to the entry block to represent
the special-purpose arguments.
- Propagate the link and sret arguments to return instructions if the
legalized signature asks for it.
When converting from ABI types to original program types, the final
conversion instruction can place its result into the original value, so
it doesn't need to be changed to an alias.
When we're splitting an EBB argument, we insert a iconcat/vconcat
instruction that computes the original value from the new split
arguments.
The concat instruction can now define the original value directly, it is
not necessary to define a new value and alias the old one.
Soon, InstructionData won't have sufficient information to compute this.
Give TargetIsa::encode() an explicit ctrl_typevar argument. This
function does not require the instruction to be inserted in the DFG
tables.
We only ever create table values now.
Simplify legalizer::legalize_inst_results. Instead of calling
detach_secondary_results, just detach all the results and don't treat
the first result specially.
We don't want to distinguish between single-result and multiple-result
instructions any longer.
- Merge the simple_instruction() and complex_instruction() builder
methods into a single build() that can handle all cases.
- All format constructors now take a ctrl_type argument. Previously,
some would take a result_type argument.
- Instruction constructors no longer attempt to compute a single result
type. Just pass a ctrl_type and let the backend decide.
Fix one format constructor call in legalizer/split.rs which now takes a
ctrl_type instead of a result type.
Now we can access instruction results and arguments as well as EBB
arguments as slices.
Delete the Values iterator which was traversing the linked lists of
values. It is no longer needed.
Rather than returning the head of a linked list of EBB arguments, just
return the whole value list of all the arguments.
Delete the next_ebb_arg() method which was only used for traversing that
list.
* Verify that a recomputed dominator tree is identical to the existing one.
* The verifier now typechecks instruction results and arguments.
* The verifier now typechecks instruction results and arguments.
* The verifier now typechecks instruction results and arguments.
* Added `inst_{fixed,variable}_args` accessor functions.
* Improved error messages in verifier.
* Type check return statements against the function signature.
This means that whenever we need to split a value, it is either already
defined by a concatenation instruction in a previously processed EBB, or
it's an EBB argument.
The EBB argument splitting may generate concat-split dependencies when
it repairs branch arguments in EBBs that have not yet been fully
legalized. Add a branch argument simplification step that can resolve
these dependency chains.
This means that all split and concatenation instructions will be dead
after legalization for types that have no legal instructions using them.
When the legalizer splits a value into halves, it would previously stop
if the value was an EBB argument. With this change, we also split EBB
arguments and iteratively split arguments on branches to the EBB.
The iterative splitting stops when we hit the entry block arguments or
an instruction that isn't one of the concatenation instructions.
Legalizing some instructions may require modifications to the control
flow graph, and some operations need to use the CFG analysis.
The CFG reference is threaded through all the legalization functions to
reach the generated expansion functions as well as the legalizer::split
module where it will be used first.
The legalizer often splits values into parts with the vsplit and
isplit_lohi instructions. Avoid doing that for values that are already
defined by the corresponding concatenation instructions.
This reduces the number of instructions created during legalization, and
it simplifies later optimizations. A number of dead concatenation
instructions are left behind. They can be trivially cleaned up by a dead
code elimination pass.
