When coloring registers for a branch instruction, also make sure that
the values passed as EBB arguments are in the registers expected by the
EBB.
The first time a branch to an EBB is processed, assign the EBB arguments
to the registers where the branch arguments already reside so no
regmoves are needed.
Coalescing means creating virtual registers and transforming the code
into conventional SSA form. This means that every value used as a branch
argument will belong to the same virtual register as the corresponding
EBB argument value.
Conventional SSA form makes it easy to avoid memory-memory copies when
spilling values, and the virtual registers can be used as hints when
picking registers too. This reduces the number of register moves needed
for EBB arguments.
As soon as a value is spilled, also assign it to a spill slot.
For now, create a new spill slot for each spilled value. In the future,
values will be sharing spill slots of they are phi-related.
An instruction may have fixed operand constraints that make it
impossibly to use a single register value to satisfy two at a time.
Detect when the same value is used for multiple fixed register operands
and insert copies during the spilling pass.
Add a spilling pass which lowers register pressure by assigning SSA
values to the stack. Important missing features:
- Resolve conflicts where an instruction uses the same value more than
once in incompatible ways.
- Deal with EBB arguments.
Fix bugs in the reload pass exposed by the first test case:
- Create live ranges for temporary registers.
- Set encodings on created spill and fill instructions.
* Function names should start with %
* Create FunctionName from string
* Implement displaying of FunctionName as %nnnn with fallback to #xxxx
* Run rustfmt and fix FunctionName::with_string in parser
* Implement FunctionName::new as a generic function
* Binary function names should start with #
* Implement NameRepr for function name
* Fix examples in docs to reflect that function names start with %
* Rebase and fix filecheck tests
The live value tracker expects them to be there.
We may eventually delete dead arguments from internal EBBs, but at least
the entry block needs to be able to handle dead function arguments.
The arguments to the entry block arrive in registers determined by the
ABI. This information is stored in the signature.
Use a separate function for coloring entry block arguments using the
signature information. We can't handle stack arguments yet.
