The control flow graph does not guarantee any particular ordering for
its successor lists, and the post-order we are computing for building
the dominator tree needs to be "split-invariant".
See #146 for details.
- Discover EBB successors directly from the EBB instruction sequence to
guarantee that the post-order we compute is canonical/split-invariant.
- Use an alternative graph DFS algorithm which doesn't require indexing
into a slice of successors.
This changes cfg_postorder in some cases because the edge pruning when
converting the (DAG) CFG to a tree for the DFT is different.
The default container is empty. We need a manual implementation of
Default because deriving it seems to imply that K and V generic
parameter types must also implement Default.
Cloning can be used to clone an empty container or for cloning the whole
forest. We can derive this trait because we already require Copy for K
and V.
The iter() methods return an iterator that traverses all set elements /
map key-value pairs. The iterator doesn't require a mutable container
and forest reference, unlike the cursor types.
Add new ordered set and map data structures based on B+-trees. These are
not general-purpose data structures like the BTreeSet and BTreeMap types
in the standard library. They are specialized for:
- Keys and values are small `Copy` types, optimized for 32-bit entities.
- Each set or map has a very small footprint, using only 32 bits of
memory when empty.
- Keys are compared using a borrowed comparator object which can provide
context for comparing tiny types that don't contain enough information
to implement `Ord`.
- A whole forest of B-trees can be cleared in constant time without
having to traverse the whole data structure.
Fixes#178.
When an instruction with a fixed output operand defines a globally live
SSA value, we need to check if the fixed register is available in the
`regs.global` set of registers that can be used across EBB boundaries.
If the fixed output register is not available in regs.global, set the
replace_global_defines flag so the output operands are rewritten as
local values.
Fixes#175.
The Intel division instructions have fixed input operands that are
clobbered by fixed output operands, so the value passed as an input will
be clobbered just like a tied operand.
The FixedTied operand constraint is used to indicate a fixed input
operand that has a corresponding output operand with the same fixed
register.
Teach the spiller to teach a FixedTied operand the same as a Tied
operand constraint and make sure that the input value is killed by the
instruction.
Rename the ArgumentType type to AbiParam since it describes the ABI
characteristics of a parameter or return value, not just the value type.
In Signature, rename members argument_types and return_types to "params"
and "returns". Again, they are not just types.
Fix a couple lingering references to "EBB arguments".
Add EBB parameter and EBB argument to the langref glossary to clarify
the distinction between formal EBB parameter values and arguments passed
to branches.
- Replace "ebb_arg" with "ebb_param" in function names that deal with
EBB parameters.
- Rename the ValueDef variants to Result and Param.
- A bunch of other small langref fixes.
No functional changes intended.
Also move the CursorPosition type into the cursor module.
Move layout::cursor into the tests module as LayoutCursor and remove its
ability to insert instructions via the dfg.ins() method. This cursor
type is only used in the layout unit tests now.
The FuncCursor and EncCursor types are the commonly used cursors now.
On some ISAs like Intel's, all arithmetic instructions set all or some
of the CPU flags, so flag values can't be live across these
instructions. On ISAs like ARM's Aarch32, flags are clobbered by compact
16-bit encodings but not necessarily by 32-bit encodings of the same
instruction.
The "clobbers_flags" bit on the encoding recipe is used to indicate if
CPU flag values can be live across an instruction, or conversely whether
the encoding can be used where flag values are live.
