//! A SSA-building API that handles incomplete CFGs.
//!
//! The algorithm is based upon Braun M., Buchwald S., Hack S., Leißa R., Mallon C.,
//! Zwinkau A. (2013) Simple and Efficient Construction of Static Single Assignment Form.
//! In: Jhala R., De Bosschere K. (eds) Compiler Construction. CC 2013.
//! Lecture Notes in Computer Science, vol 7791. Springer, Berlin, Heidelberg
//!
//! <https://link.springer.com/content/pdf/10.1007/978-3-642-37051-9_6.pdf>
use crate::Variable;
use alloc::vec::Vec;
use core::convert::TryInto;
use core::mem;
use cranelift_codegen::cursor::{Cursor, FuncCursor};
use cranelift_codegen::entity::{EntityList, EntitySet, ListPool, SecondaryMap};
use cranelift_codegen::ir::immediates::{Ieee32, Ieee64};
use cranelift_codegen::ir::types::{F32, F64, I128, I64};
use cranelift_codegen::ir::{Block, Function, Inst, InstBuilder, Type, Value};
use cranelift_codegen::packed_option::PackedOption;
/// Structure containing the data relevant the construction of SSA for a given function.
///
/// The parameter struct `Variable` corresponds to the way variables are represented in the
/// non-SSA language you're translating from.
///
/// The SSA building relies on information about the variables used and defined.
///
/// This SSA building module allows you to def and use variables on the fly while you are
/// constructing the CFG, no need for a separate SSA pass after the CFG is completed.
///
/// A basic block is said _filled_ if all the instruction that it contains have been translated,
/// and it is said _sealed_ if all of its predecessors have been declared. Only filled predecessors
/// can be declared.
#[derive(Default)]
pub struct SSABuilder {
// TODO: Consider a sparse representation rather than SecondaryMap-of-SecondaryMap.
/// Records for every variable and for every relevant block, the last definition of
/// the variable in the block.
variables: SecondaryMap<Variable, SecondaryMap<Block, PackedOption<Value>>>,
/// Records the position of the basic blocks and the list of values used but not defined in the
/// block.
ssa_blocks: SecondaryMap<Block, SSABlockData>,
/// Call stack for use in the `use_var`/`predecessors_lookup` state machine.
calls: Vec<Call>,
/// Result stack for use in the `use_var`/`predecessors_lookup` state machine.
results: Vec<Value>,
/// Side effects accumulated in the `use_var`/`predecessors_lookup` state machine.
side_effects: SideEffects,
/// Reused storage for cycle-detection.
visited: EntitySet<Block>,
/// Storage for pending variable definitions.
variable_pool: ListPool<Variable>,
/// Storage for predecessor definitions.
inst_pool: ListPool<Inst>,
}
/// Side effects of a `use_var` or a `seal_block` method call.
#[derive(Default)]
pub struct SideEffects {
/// When a variable is used but has never been defined before (this happens in the case of
/// unreachable code), a placeholder `iconst` or `fconst` value is added to the right `Block`.
/// This field signals if it is the case and return the `Block` to which the initialization has
/// been added.
pub instructions_added_to_blocks: Vec<Block>,
}
impl SideEffects {
fn is_empty(&self) -> bool {
self.instructions_added_to_blocks.is_empty()
}
}
#[derive(Clone)]
enum Sealed {
No {
// List of current Block arguments for which an earlier def has not been found yet.
undef_variables: EntityList<Variable>,
},
Yes,
}
impl Default for Sealed {
fn default() -> Self {
Sealed::No {
undef_variables: EntityList::new(),
}
}
}
#[derive(Clone, Default)]
struct SSABlockData {
// The predecessors of the Block with the block and branch instruction.
predecessors: EntityList<Inst>,
// A block is sealed if all of its predecessors have been declared.
sealed: Sealed,
// If this block is sealed and it has exactly one predecessor, this is that predecessor.
single_predecessor: PackedOption<Block>,
}
impl SSABuilder {
/// Clears a `SSABuilder` from all its data, letting it in a pristine state without
/// deallocating memory.
pub fn clear(&mut self) {
self.variables.clear();
self.ssa_blocks.clear();
self.variable_pool.clear();
self.inst_pool.clear();
debug_assert!(self.calls.is_empty());
debug_assert!(self.results.is_empty());
debug_assert!(self.side_effects.is_empty());
}
/// Tests whether an `SSABuilder` is in a cleared state.
pub fn is_empty(&self) -> bool {
self.variables.is_empty()
&& self.ssa_blocks.is_empty()
&& self.calls.is_empty()
&& self.results.is_empty()
&& self.side_effects.is_empty()
}
}
/// States for the `use_var`/`predecessors_lookup` state machine.
enum Call {
UseVar(Inst),
FinishPredecessorsLookup(Value, Block),
}
/// Emit instructions to produce a zero value in the given type.
fn emit_zero(ty: Type, mut cur: FuncCursor) -> Value {
if ty == I128 {
let zero = cur.ins().iconst(I64, 0);
cur.ins().uextend(I128, zero)
} else if ty.is_int() {
cur.ins().iconst(ty, 0)
} else if ty == F32 {
cur.ins().f32const(Ieee32::with_bits(0))
} else if ty == F64 {
cur.ins().f64const(Ieee64::with_bits(0))
} else if ty.is_ref() {
cur.ins().null(ty)
} else if ty.is_vector() {
let scalar_ty = ty.lane_type();
if scalar_ty.is_int() {
let zero = cur.func.dfg.constants.insert(
core::iter::repeat(0)
.take(ty.bytes().try_into().unwrap())
.collect(),
);
cur.ins().vconst(ty, zero)
} else if scalar_ty == F32 {
let scalar = cur.ins().f32const(Ieee32::with_bits(0));
cur.ins().splat(ty, scalar)
} else if scalar_ty == F64 {
let scalar = cur.ins().f64const(Ieee64::with_bits(0));
cur.ins().splat(ty, scalar)
} else {
panic!("unimplemented scalar type: {:?}", ty)
}
} else {
panic!("unimplemented type: {:?}", ty)
}
}
/// The following methods are the API of the SSA builder. Here is how it should be used when
/// translating to Cranelift IR:
///
/// - for each basic block, create a corresponding data for SSA construction with `declare_block`;
///
/// - while traversing a basic block and translating instruction, use `def_var` and `use_var`
/// to record definitions and uses of variables, these methods will give you the corresponding
/// SSA values;
///
/// - when all the instructions in a basic block have translated, the block is said _filled_ and
/// only then you can add it as a predecessor to other blocks with `declare_block_predecessor`;
///
/// - when you have constructed all the predecessor to a basic block,
/// call `seal_block` on it with the `Function` that you are building.
///
/// This API will give you the correct SSA values to use as arguments of your instructions,
/// as well as modify the jump instruction and `Block` parameters to account for the SSA
/// Phi functions.
///
impl SSABuilder {
/// Declares a new definition of a variable in a given basic block.
/// The SSA value is passed as an argument because it should be created with
/// `ir::DataFlowGraph::append_result`.
pub fn def_var(&mut self, var: Variable, val: Value, block: Block) {
self.variables[var][block] = PackedOption::from(val);
}
/// Declares a use of a variable in a given basic block. Returns the SSA value corresponding
/// to the current SSA definition of this variable and a list of newly created Blocks that
/// are the results of critical edge splitting for `br_table` with arguments.
///
/// If the variable has never been defined in this blocks or recursively in its predecessors,
/// this method will silently create an initializer with `iconst` or `fconst`. You are
/// responsible for making sure that you initialize your variables.
pub fn use_var(
&mut self,
func: &mut Function,
var: Variable,
ty: Type,
block: Block,
) -> (Value, SideEffects) {
debug_assert!(self.calls.is_empty());
debug_assert!(self.results.is_empty());
debug_assert!(self.side_effects.is_empty());
// Prepare the 'calls' and 'results' stacks for the state machine.
self.use_var_nonlocal(func, var, ty, block);
let value = self.run_state_machine(func, var, ty);
let side_effects = mem::take(&mut self.side_effects);
(value, side_effects)
}
/// Resolve the minimal SSA Value of `var` in `block` by traversing predecessors.
///
/// This function sets up state for `run_state_machine()` but does not execute it.
fn use_var_nonlocal(&mut self, func: &mut Function, var: Variable, ty: Type, mut block: Block) {
// First, try Local Value Numbering (Algorithm 1 in the paper).
// If the variable already has a known Value in this block, use that.
if let Some(val) = self.variables[var][block].expand() {
self.results.push(val);
return;
}
// Otherwise, use Global Value Numbering (Algorithm 2 in the paper).
// This resolves the Value with respect to its predecessors.
// Find the most recent definition of `var`, and the block the definition comes from.
let (val, from) = self.find_var(func, var, ty, block);
// The `from` block returned from `find_var` is guaranteed to be on the path we follow by
// traversing only single-predecessor edges. It might be equal to `block` if there is no
// such path, but in that case `find_var` ensures that the variable is defined in this block
// by a new block parameter. It also might be somewhere in a cycle, but even then this loop
// will terminate the first time it encounters that block, rather than continuing around the
// cycle forever.
//
// Why is it okay to copy the definition to all intervening blocks? For the initial block,
// this may not be the final definition of this variable within this block, but if we've
// gotten here then we know there is no earlier definition in the block already.
//
// For the remaining blocks: Recall that a block is only allowed to be set as a predecessor
// after all its instructions have already been filled in, so when we follow a predecessor
// edge to a block, we know there will never be any more local variable definitions added to
// that block. We also know that `find_var` didn't find a definition for this variable in
// any of the blocks before `from`.
//
// So in either case there is no definition in these blocks yet and we can blindly set one.
let var_defs = &mut self.variables[var];
while block != from {
debug_assert!(var_defs[block].is_none());
var_defs[block] = PackedOption::from(val);
block = self.ssa_blocks[block].single_predecessor.unwrap();
}
}
/// Find the most recent definition of this variable, returning both the definition and the
/// block in which it was found. If we can't find a definition that's provably the right one for
/// all paths to the current block, then append a block parameter to some block and use that as
/// the definition. Either way, also arrange that the definition will be on the `results` stack
/// when `run_state_machine` is done processing the current step.
///
/// If a block has exactly one predecessor, and the block is sealed so we know its predecessors
/// will never change, then its definition for this variable is the same as the definition from
/// that one predecessor. In this case it's easy to see that no block parameter is necessary,
/// but we need to look at the predecessor to see if a block parameter might be needed there.
/// That holds transitively across any chain of sealed blocks with exactly one predecessor each.
///
/// This runs into a problem, though, if such a chain has a cycle: Blindly following a cyclic
/// chain that never defines this variable would lead to an infinite loop in the compiler. It
/// doesn't really matter what code we generate in that case. Since each block in the cycle has
/// exactly one predecessor, there's no way to enter the cycle from the function's entry block;
/// and since all blocks in the cycle are sealed, the entire cycle is permanently dead code. But
/// we still have to prevent the possibility of an infinite loop.
///
/// To break cycles, we can pick any block within the cycle as the one where we'll add a block
/// parameter. It's convenient to pick the block at which we entered the cycle, because that's
/// the first place where we can detect that we just followed a cycle. Adding a block parameter
/// gives us a definition we can reuse throughout the rest of the cycle.
fn find_var(
&mut self,
func: &mut Function,
var: Variable,
ty: Type,
mut block: Block,
) -> (Value, Block) {
// Try to find an existing definition along single-predecessor edges first.
self.visited.clear();
let var_defs = &mut self.variables[var];
while let Some(pred) = self.ssa_blocks[block].single_predecessor.expand() {
if !self.visited.insert(block) {
break;
}
block = pred;
if let Some(val) = var_defs[block].expand() {
self.results.push(val);
return (val, block);
}
}
// We've promised to return the most recent block where `var` was defined, but we didn't
// find a usable definition. So create one.
let val = func.dfg.append_block_param(block, ty);
var_defs[block] = PackedOption::from(val);
// Now every predecessor needs to pass its definition of this variable to the newly added
// block parameter. To do that we have to "recursively" call `use_var`, but there are two
// problems with doing that. First, we need to keep a fixed bound on stack depth, so we
// can't actually recurse; instead we defer to `run_state_machine`. Second, if we don't
// know all our predecessors yet, we have to defer this work until the block gets sealed.
match &mut self.ssa_blocks[block].sealed {
// Once all the `calls` added here complete, this leaves either `val` or an equivalent
// definition on the `results` stack.
Sealed::Yes => self.begin_predecessors_lookup(val, block),
Sealed::No { undef_variables } => {
undef_variables.push(var, &mut self.variable_pool);
self.results.push(val);
}
}
(val, block)
}
/// Declares a new basic block to construct corresponding data for SSA construction.
/// No predecessors are declared here and the block is not sealed.
/// Predecessors have to be added with `declare_block_predecessor`.
pub fn declare_block(&mut self, block: Block) {
// Ensure the block exists so seal_all_blocks will see it even if no predecessors or
// variables get declared for this block. But don't assign anything to it:
// SecondaryMap automatically sets all blocks to `default()`.
let _ = &mut self.ssa_blocks[block];
}
/// Declares a new predecessor for a `Block` and record the branch instruction
/// of the predecessor that leads to it.
///
/// The precedent `Block` must be filled before added as predecessor.
/// Note that you must provide no jump arguments to the branch
/// instruction when you create it since `SSABuilder` will fill them for you.
///
/// Callers are expected to avoid adding the same predecessor more than once in the case
/// of a jump table.
pub fn declare_block_predecessor(&mut self, block: Block, inst: Inst) {
debug_assert!(!self.is_sealed(block));
self.ssa_blocks[block]
.predecessors
.push(inst, &mut self.inst_pool);
}
/// Remove a previously declared Block predecessor by giving a reference to the jump
/// instruction. Returns the basic block containing the instruction.
///
/// Note: use only when you know what you are doing, this might break the SSA building problem
pub fn remove_block_predecessor(&mut self, block: Block, inst: Inst) {
debug_assert!(!self.is_sealed(block));
let data = &mut self.ssa_blocks[block];
let pred = data
.predecessors
.as_slice(&self.inst_pool)
.iter()
.position(|&branch| branch == inst)
.expect("the predecessor you are trying to remove is not declared");
data.predecessors.swap_remove(pred, &mut self.inst_pool);
}
/// Completes the global value numbering for a `Block`, all of its predecessors having been
/// already sealed.
///
/// This method modifies the function's `Layout` by adding arguments to the `Block`s to
/// take into account the Phi function placed by the SSA algorithm.
///
/// Returns the list of newly created blocks for critical edge splitting.
pub fn seal_block(&mut self, block: Block, func: &mut Function) -> SideEffects {
debug_assert!(
!self.is_sealed(block),
"Attempting to seal {} which is already sealed.",
block
);
self.seal_one_block(block, func);
mem::take(&mut self.side_effects)
}
/// Completes the global value numbering for all unsealed `Block`s in `func`.
///
/// It's more efficient to seal `Block`s as soon as possible, during
/// translation, but for frontends where this is impractical to do, this
/// function can be used at the end of translating all blocks to ensure
/// that everything is sealed.
pub fn seal_all_blocks(&mut self, func: &mut Function) -> SideEffects {
// Seal all `Block`s currently in the function. This can entail splitting
// and creation of new blocks, however such new blocks are sealed on
// the fly, so we don't need to account for them here.
for block in self.ssa_blocks.keys() {
self.seal_one_block(block, func);
}
mem::take(&mut self.side_effects)
}
/// Helper function for `seal_block` and `seal_all_blocks`.
fn seal_one_block(&mut self, block: Block, func: &mut Function) {
// For each undef var we look up values in the predecessors and create a block parameter
// only if necessary.
let mut undef_variables =
match mem::replace(&mut self.ssa_blocks[block].sealed, Sealed::Yes) {
Sealed::No { undef_variables } => undef_variables,
Sealed::Yes => return,
};
let ssa_params = undef_variables.len(&self.variable_pool);
let predecessors = self.predecessors(block);
if predecessors.len() == 1 {
let pred = func.layout.inst_block(predecessors[0]).unwrap();
self.ssa_blocks[block].single_predecessor = PackedOption::from(pred);
}
// Note that begin_predecessors_lookup requires visiting these variables in the same order
// that they were defined by find_var, because it appends arguments to the jump instructions
// in all the predecessor blocks one variable at a time.
for idx in 0..ssa_params {
let var = undef_variables.get(idx, &self.variable_pool).unwrap();
// We need the temporary Value that was assigned to this Variable. If that Value shows
// up as a result from any of our predecessors, then it never got assigned on the loop
// through that block. We get the value from the next block param, where it was first
// allocated in find_var.
let block_params = func.dfg.block_params(block);
// On each iteration through this loop, there are (ssa_params - idx) undefined variables
// left to process. Previous iterations through the loop may have removed earlier block
// parameters, but the last (ssa_params - idx) block parameters always correspond to the
// remaining undefined variables. So index from the end of the current block params.
let val = block_params[block_params.len() - (ssa_params - idx)];
debug_assert!(self.calls.is_empty());
debug_assert!(self.results.is_empty());
// self.side_effects may be non-empty here so that callers can
// accumulate side effects over multiple calls.
self.begin_predecessors_lookup(val, block);
self.run_state_machine(func, var, func.dfg.value_type(val));
}
undef_variables.clear(&mut self.variable_pool);
}
/// Given the local SSA Value of a Variable in a Block, perform a recursive lookup on
/// predecessors to determine if it is redundant with another Value earlier in the CFG.
///
/// If such a Value exists and is redundant, the local Value is replaced by the
/// corresponding non-local Value. If the original Value was a Block parameter,
/// the parameter may be removed if redundant. Parameters are placed eagerly by callers
/// to avoid infinite loops when looking up a Value for a Block that is in a CFG loop.
///
/// Doing this lookup for each Value in each Block preserves SSA form during construction.
///
/// ## Arguments
///
/// `sentinel` is a dummy Block parameter inserted by `use_var_nonlocal()`.
/// Its purpose is to allow detection of CFG cycles while traversing predecessors.
fn begin_predecessors_lookup(&mut self, sentinel: Value, dest_block: Block) {
self.calls
.push(Call::FinishPredecessorsLookup(sentinel, dest_block));
// Iterate over the predecessors.
self.calls.extend(
self.ssa_blocks[dest_block]
.predecessors
.as_slice(&self.inst_pool)
.iter()
.rev()
.copied()
.map(Call::UseVar),
);
}
/// Examine the values from the predecessors and compute a result value, creating
/// block parameters as needed.
fn finish_predecessors_lookup(
&mut self,
func: &mut Function,
sentinel: Value,
dest_block: Block,
) -> Value {
// Determine how many predecessors are yielding unique, non-temporary Values. If a variable
// is live and unmodified across several control-flow join points, earlier blocks will
// introduce aliases for that variable's definition, so we resolve aliases eagerly here to
// ensure that we can tell when the same definition has reached this block via multiple
// paths. Doing so also detects cyclic references to the sentinel, which can occur in
// unreachable code.
let num_predecessors = self.predecessors(dest_block).len();
// When this `Drain` is dropped, these elements will get truncated.
let results = self.results.drain(self.results.len() - num_predecessors..);
let pred_val = {
let mut iter = results
.as_slice()
.iter()
.map(|&val| func.dfg.resolve_aliases(val))
.filter(|&val| val != sentinel);
if let Some(val) = iter.next() {
// This variable has at least one non-temporary definition. If they're all the same
// value, we can remove the block parameter and reference that value instead.
if iter.all(|other| other == val) {
Some(val)
} else {
None
}
} else {
// The variable is used but never defined before. This is an irregularity in the
// code, but rather than throwing an error we silently initialize the variable to
// 0. This will have no effect since this situation happens in unreachable code.
if !func.layout.is_block_inserted(dest_block) {
func.layout.append_block(dest_block);
}
self.side_effects
.instructions_added_to_blocks
.push(dest_block);
let zero = emit_zero(
func.dfg.value_type(sentinel),
FuncCursor::new(func).at_first_insertion_point(dest_block),
);
Some(zero)
}
};
if let Some(pred_val) = pred_val {
// Here all the predecessors use a single value to represent our variable
// so we don't need to have it as a block argument.
// We need to replace all the occurrences of val with pred_val but since
// we can't afford a re-writing pass right now we just declare an alias.
func.dfg.remove_block_param(sentinel);
func.dfg.change_to_alias(sentinel, pred_val);
pred_val
} else {
// There is disagreement in the predecessors on which value to use so we have
// to keep the block argument.
let mut preds = self.ssa_blocks[dest_block].predecessors;
let dfg = &mut func.stencil.dfg;
for (idx, &val) in results.as_slice().iter().enumerate() {
let pred = preds.get_mut(idx, &mut self.inst_pool).unwrap();
let branch = *pred;
let dests = dfg.insts[branch].branch_destination_mut(&mut dfg.jump_tables);
assert!(
!dests.is_empty(),
"you have declared a non-branch instruction as a predecessor to a block!"
);
for block in dests {
if block.block(&dfg.value_lists) == dest_block {
block.append_argument(val, &mut dfg.value_lists);
}
}
}
sentinel
}
}
/// Returns the list of `Block`s that have been declared as predecessors of the argument.
fn predecessors(&self, block: Block) -> &[Inst] {
self.ssa_blocks[block]
.predecessors
.as_slice(&self.inst_pool)
}
/// Returns whether the given Block has any predecessor or not.
pub fn has_any_predecessors(&self, block: Block) -> bool {
!self.predecessors(block).is_empty()
}
/// Returns `true` if and only if `seal_block` has been called on the argument.
pub fn is_sealed(&self, block: Block) -> bool {
matches!(self.ssa_blocks[block].sealed, Sealed::Yes)
}
/// The main algorithm is naturally recursive: when there's a `use_var` in a
/// block with no corresponding local defs, it recurses and performs a
/// `use_var` in each predecessor. To avoid risking running out of callstack
/// space, we keep an explicit stack and use a small state machine rather
/// than literal recursion.
fn run_state_machine(&mut self, func: &mut Function, var: Variable, ty: Type) -> Value {
// Process the calls scheduled in `self.calls` until it is empty.
while let Some(call) = self.calls.pop() {
match call {
Call::UseVar(branch) => {
let block = func.layout.inst_block(branch).unwrap();
self.use_var_nonlocal(func, var, ty, block);
}
Call::FinishPredecessorsLookup(sentinel, dest_block) => {
let val = self.finish_predecessors_lookup(func, sentinel, dest_block);
self.results.push(val);
}
}
}
debug_assert_eq!(self.results.len(), 1);
self.results.pop().unwrap()
}
}
#[cfg(test)]
mod tests {
use crate::ssa::SSABuilder;
use crate::Variable;
use cranelift_codegen::cursor::{Cursor, FuncCursor};
use cranelift_codegen::entity::EntityRef;
use cranelift_codegen::ir;
use cranelift_codegen::ir::types::*;
use cranelift_codegen::ir::{Function, Inst, InstBuilder, JumpTableData, Opcode};
use cranelift_codegen::settings;
use cranelift_codegen::verify_function;
#[test]
fn simple_block() {
let mut func = Function::new();
let mut ssa = SSABuilder::default();
let block0 = func.dfg.make_block();
// Here is the pseudo-program we want to translate:
// block0:
// x = 1;
// y = 2;
// z = x + y;
// z = x + z;
ssa.declare_block(block0);
let x_var = Variable::new(0);
let x_ssa = {
let mut cur = FuncCursor::new(&mut func);
cur.insert_block(block0);
cur.ins().iconst(I32, 1)
};
ssa.def_var(x_var, x_ssa, block0);
let y_var = Variable::new(1);
let y_ssa = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block0);
cur.ins().iconst(I32, 2)
};
ssa.def_var(y_var, y_ssa, block0);
assert_eq!(ssa.use_var(&mut func, x_var, I32, block0).0, x_ssa);
assert_eq!(ssa.use_var(&mut func, y_var, I32, block0).0, y_ssa);
let z_var = Variable::new(2);
let x_use1 = ssa.use_var(&mut func, x_var, I32, block0).0;
let y_use1 = ssa.use_var(&mut func, y_var, I32, block0).0;
let z1_ssa = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block0);
cur.ins().iadd(x_use1, y_use1)
};
ssa.def_var(z_var, z1_ssa, block0);
assert_eq!(ssa.use_var(&mut func, z_var, I32, block0).0, z1_ssa);
let x_use2 = ssa.use_var(&mut func, x_var, I32, block0).0;
let z_use1 = ssa.use_var(&mut func, z_var, I32, block0).0;
let z2_ssa = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block0);
cur.ins().iadd(x_use2, z_use1)
};
ssa.def_var(z_var, z2_ssa, block0);
assert_eq!(ssa.use_var(&mut func, z_var, I32, block0).0, z2_ssa);
}
#[test]
fn sequence_of_blocks() {
let mut func = Function::new();
let mut ssa = SSABuilder::default();
let block0 = func.dfg.make_block();
let block1 = func.dfg.make_block();
let block2 = func.dfg.make_block();
// Here is the pseudo-program we want to translate:
// block0:
// x = 1;
// y = 2;
// z = x + y;
// brif y, block1, block1;
// block1:
// z = x + z;
// jump block2;
// block2:
// y = x + y;
{
let mut cur = FuncCursor::new(&mut func);
cur.insert_block(block0);
cur.insert_block(block1);
cur.insert_block(block2);
}
// block0
ssa.declare_block(block0);
ssa.seal_block(block0, &mut func);
let x_var = Variable::new(0);
let x_ssa = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block0);
cur.ins().iconst(I32, 1)
};
ssa.def_var(x_var, x_ssa, block0);
let y_var = Variable::new(1);
let y_ssa = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block0);
cur.ins().iconst(I32, 2)
};
ssa.def_var(y_var, y_ssa, block0);
let z_var = Variable::new(2);
let x_use1 = ssa.use_var(&mut func, x_var, I32, block0).0;
let y_use1 = ssa.use_var(&mut func, y_var, I32, block0).0;
let z1_ssa = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block0);
cur.ins().iadd(x_use1, y_use1)
};
ssa.def_var(z_var, z1_ssa, block0);
let y_use2 = ssa.use_var(&mut func, y_var, I32, block0).0;
let brif_block0_block2_block1: Inst = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block0);
cur.ins().brif(y_use2, block2, &[], block1, &[])
};
assert_eq!(ssa.use_var(&mut func, x_var, I32, block0).0, x_ssa);
assert_eq!(ssa.use_var(&mut func, y_var, I32, block0).0, y_ssa);
assert_eq!(ssa.use_var(&mut func, z_var, I32, block0).0, z1_ssa);
// block1
ssa.declare_block(block1);
ssa.declare_block_predecessor(block1, brif_block0_block2_block1);
ssa.seal_block(block1, &mut func);
let x_use2 = ssa.use_var(&mut func, x_var, I32, block1).0;
let z_use1 = ssa.use_var(&mut func, z_var, I32, block1).0;
let z2_ssa = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block1);
cur.ins().iadd(x_use2, z_use1)
};
ssa.def_var(z_var, z2_ssa, block1);
let jump_block1_block2: Inst = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block1);
cur.ins().jump(block2, &[])
};
assert_eq!(x_use2, x_ssa);
assert_eq!(z_use1, z1_ssa);
assert_eq!(ssa.use_var(&mut func, z_var, I32, block1).0, z2_ssa);
// block2
ssa.declare_block(block2);
ssa.declare_block_predecessor(block2, brif_block0_block2_block1);
ssa.declare_block_predecessor(block2, jump_block1_block2);
ssa.seal_block(block2, &mut func);
let x_use3 = ssa.use_var(&mut func, x_var, I32, block2).0;
let y_use3 = ssa.use_var(&mut func, y_var, I32, block2).0;
let y2_ssa = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block2);
cur.ins().iadd(x_use3, y_use3)
};
ssa.def_var(y_var, y2_ssa, block2);
assert_eq!(x_ssa, x_use3);
assert_eq!(y_ssa, y_use3);
match func.dfg.insts[brif_block0_block2_block1] {
ir::InstructionData::Brif {
blocks: [block_then, block_else],
..
} => {
assert_eq!(block_then.block(&func.dfg.value_lists), block2);
assert_eq!(block_then.args_slice(&func.dfg.value_lists).len(), 0);
assert_eq!(block_else.block(&func.dfg.value_lists), block1);
assert_eq!(block_else.args_slice(&func.dfg.value_lists).len(), 0);
}
_ => assert!(false),
};
match func.dfg.insts[brif_block0_block2_block1] {
ir::InstructionData::Brif {
blocks: [block_then, block_else],
..
} => {
assert_eq!(block_then.block(&func.dfg.value_lists), block2);
assert_eq!(block_then.args_slice(&func.dfg.value_lists).len(), 0);
assert_eq!(block_else.block(&func.dfg.value_lists), block1);
assert_eq!(block_else.args_slice(&func.dfg.value_lists).len(), 0);
}
_ => assert!(false),
};
match func.dfg.insts[jump_block1_block2] {
ir::InstructionData::Jump {
destination: dest, ..
} => {
assert_eq!(dest.block(&func.dfg.value_lists), block2);
assert_eq!(dest.args_slice(&func.dfg.value_lists).len(), 0);
}
_ => assert!(false),
};
}
#[test]
fn program_with_loop() {
let mut func = Function::new();
let mut ssa = SSABuilder::default();
let block0 = func.dfg.make_block();
let block1 = func.dfg.make_block();
let block2 = func.dfg.make_block();
let block3 = func.dfg.make_block();
{
let mut cur = FuncCursor::new(&mut func);
cur.insert_block(block0);
cur.insert_block(block1);
cur.insert_block(block2);
cur.insert_block(block3);
}
// Here is the pseudo-program we want to translate:
// block0:
// x = 1;
// y = 2;
// z = x + y;
// jump block1
// block1:
// z = z + y;
// brif y, block3, block2;
// block2:
// z = z - x;
// return y
// block3:
// y = y - x
// jump block1
// block0
ssa.declare_block(block0);
ssa.seal_block(block0, &mut func);
let x_var = Variable::new(0);
let x1 = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block0);
cur.ins().iconst(I32, 1)
};
ssa.def_var(x_var, x1, block0);
let y_var = Variable::new(1);
let y1 = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block0);
cur.ins().iconst(I32, 2)
};
ssa.def_var(y_var, y1, block0);
let z_var = Variable::new(2);
let x2 = ssa.use_var(&mut func, x_var, I32, block0).0;
let y2 = ssa.use_var(&mut func, y_var, I32, block0).0;
let z1 = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block0);
cur.ins().iadd(x2, y2)
};
ssa.def_var(z_var, z1, block0);
let jump_block0_block1 = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block0);
cur.ins().jump(block1, &[])
};
assert_eq!(ssa.use_var(&mut func, x_var, I32, block0).0, x1);
assert_eq!(ssa.use_var(&mut func, y_var, I32, block0).0, y1);
assert_eq!(x2, x1);
assert_eq!(y2, y1);
// block1
ssa.declare_block(block1);
ssa.declare_block_predecessor(block1, jump_block0_block1);
let z2 = ssa.use_var(&mut func, z_var, I32, block1).0;
let y3 = ssa.use_var(&mut func, y_var, I32, block1).0;
let z3 = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block1);
cur.ins().iadd(z2, y3)
};
ssa.def_var(z_var, z3, block1);
let y4 = ssa.use_var(&mut func, y_var, I32, block1).0;
assert_eq!(y4, y3);
let brif_block1_block3_block2 = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block1);
cur.ins().brif(y4, block3, &[], block2, &[])
};
// block2
ssa.declare_block(block2);
ssa.declare_block_predecessor(block2, brif_block1_block3_block2);
ssa.seal_block(block2, &mut func);
let z4 = ssa.use_var(&mut func, z_var, I32, block2).0;
assert_eq!(z4, z3);
let x3 = ssa.use_var(&mut func, x_var, I32, block2).0;
let z5 = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block2);
cur.ins().isub(z4, x3)
};
ssa.def_var(z_var, z5, block2);
let y5 = ssa.use_var(&mut func, y_var, I32, block2).0;
assert_eq!(y5, y3);
{
let mut cur = FuncCursor::new(&mut func).at_bottom(block2);
cur.ins().return_(&[y5])
};
// block3
ssa.declare_block(block3);
ssa.declare_block_predecessor(block3, brif_block1_block3_block2);
ssa.seal_block(block3, &mut func);
let y6 = ssa.use_var(&mut func, y_var, I32, block3).0;
assert_eq!(y6, y3);
let x4 = ssa.use_var(&mut func, x_var, I32, block3).0;
assert_eq!(x4, x3);
let y7 = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block3);
cur.ins().isub(y6, x4)
};
ssa.def_var(y_var, y7, block3);
let jump_block3_block1 = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block3);
cur.ins().jump(block1, &[])
};
// block1 after all predecessors have been visited.
ssa.declare_block_predecessor(block1, jump_block3_block1);
ssa.seal_block(block1, &mut func);
assert_eq!(func.dfg.block_params(block1)[0], z2);
assert_eq!(func.dfg.block_params(block1)[1], y3);
assert_eq!(func.dfg.resolve_aliases(x3), x1);
}
#[test]
fn br_table_with_args() {
// This tests the on-demand splitting of critical edges for br_table with jump arguments
//
// Here is the pseudo-program we want to translate:
//
// function %f {
// block0:
// x = 1;
// br_table x, block2, [block2, block1]
// block1:
// x = 2
// jump block2
// block2:
// x = x + 1
// return
// }
let mut func = Function::new();
let mut ssa = SSABuilder::default();
let block0 = func.dfg.make_block();
let block1 = func.dfg.make_block();
let block2 = func.dfg.make_block();
{
let mut cur = FuncCursor::new(&mut func);
cur.insert_block(block0);
cur.insert_block(block1);
cur.insert_block(block2);
}
// block0
let x1 = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block0);
cur.ins().iconst(I32, 1)
};
ssa.declare_block(block0);
ssa.seal_block(block0, &mut func);
let x_var = Variable::new(0);
ssa.def_var(x_var, x1, block0);
ssa.use_var(&mut func, x_var, I32, block0).0;
let br_table = {
let jump_table = JumpTableData::new(
func.dfg.block_call(block2, &[]),
&[
func.dfg.block_call(block2, &[]),
func.dfg.block_call(block1, &[]),
],
);
let jt = func.create_jump_table(jump_table);
let mut cur = FuncCursor::new(&mut func).at_bottom(block0);
cur.ins().br_table(x1, jt)
};
// block1
ssa.declare_block(block1);
ssa.declare_block_predecessor(block1, br_table);
ssa.seal_block(block1, &mut func);
let x2 = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block1);
cur.ins().iconst(I32, 2)
};
ssa.def_var(x_var, x2, block1);
let jump_block1_block2 = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block1);
cur.ins().jump(block2, &[])
};
// block2
ssa.declare_block(block2);
ssa.declare_block_predecessor(block2, jump_block1_block2);
ssa.declare_block_predecessor(block2, br_table);
ssa.seal_block(block2, &mut func);
let x3 = ssa.use_var(&mut func, x_var, I32, block2).0;
let x4 = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block2);
cur.ins().iadd_imm(x3, 1)
};
ssa.def_var(x_var, x4, block2);
{
let mut cur = FuncCursor::new(&mut func).at_bottom(block2);
cur.ins().return_(&[])
};
let flags = settings::Flags::new(settings::builder());
match verify_function(&func, &flags) {
Ok(()) => {}
Err(_errors) => {
#[cfg(feature = "std")]
panic!("{}", _errors);
#[cfg(not(feature = "std"))]
panic!("function failed to verify");
}
}
}
#[test]
fn undef_values_reordering() {
// Here is the pseudo-program we want to translate:
// block0:
// x = 0;
// y = 1;
// z = 2;
// jump block1;
// block1:
// x = z + x;
// y = y - x;
// jump block1;
//
let mut func = Function::new();
let mut ssa = SSABuilder::default();
let block0 = func.dfg.make_block();
let block1 = func.dfg.make_block();
{
let mut cur = FuncCursor::new(&mut func);
cur.insert_block(block0);
cur.insert_block(block1);
}
// block0
ssa.declare_block(block0);
let x_var = Variable::new(0);
ssa.seal_block(block0, &mut func);
let x1 = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block0);
cur.ins().iconst(I32, 0)
};
ssa.def_var(x_var, x1, block0);
let y_var = Variable::new(1);
let y1 = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block0);
cur.ins().iconst(I32, 1)
};
ssa.def_var(y_var, y1, block0);
let z_var = Variable::new(2);
let z1 = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block0);
cur.ins().iconst(I32, 2)
};
ssa.def_var(z_var, z1, block0);
let jump_block0_block1 = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block0);
cur.ins().jump(block1, &[])
};
// block1
ssa.declare_block(block1);
ssa.declare_block_predecessor(block1, jump_block0_block1);
let z2 = ssa.use_var(&mut func, z_var, I32, block1).0;
assert_eq!(func.dfg.block_params(block1)[0], z2);
let x2 = ssa.use_var(&mut func, x_var, I32, block1).0;
assert_eq!(func.dfg.block_params(block1)[1], x2);
let x3 = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block1);
cur.ins().iadd(x2, z2)
};
ssa.def_var(x_var, x3, block1);
let x4 = ssa.use_var(&mut func, x_var, I32, block1).0;
let y3 = ssa.use_var(&mut func, y_var, I32, block1).0;
assert_eq!(func.dfg.block_params(block1)[2], y3);
let y4 = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block1);
cur.ins().isub(y3, x4)
};
ssa.def_var(y_var, y4, block1);
let jump_block1_block1 = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block1);
cur.ins().jump(block1, &[])
};
ssa.declare_block_predecessor(block1, jump_block1_block1);
ssa.seal_block(block1, &mut func);
// At sealing the "z" argument disappear but the remaining "x" and "y" args have to be
// in the right order.
assert_eq!(func.dfg.block_params(block1)[1], y3);
assert_eq!(func.dfg.block_params(block1)[0], x2);
}
#[test]
fn undef() {
// Use vars of various types which have not been defined.
let mut func = Function::new();
let mut ssa = SSABuilder::default();
let block0 = func.dfg.make_block();
ssa.declare_block(block0);
ssa.seal_block(block0, &mut func);
let i32_var = Variable::new(0);
let f32_var = Variable::new(1);
let f64_var = Variable::new(2);
let i8_var = Variable::new(3);
let f32x4_var = Variable::new(4);
ssa.use_var(&mut func, i32_var, I32, block0);
ssa.use_var(&mut func, f32_var, F32, block0);
ssa.use_var(&mut func, f64_var, F64, block0);
ssa.use_var(&mut func, i8_var, I8, block0);
ssa.use_var(&mut func, f32x4_var, F32X4, block0);
assert_eq!(func.dfg.num_block_params(block0), 0);
}
#[test]
fn undef_in_entry() {
// Use a var which has not been defined. The search should hit the
// top of the entry block, and then fall back to inserting an iconst.
let mut func = Function::new();
let mut ssa = SSABuilder::default();
let block0 = func.dfg.make_block();
ssa.declare_block(block0);
ssa.seal_block(block0, &mut func);
let x_var = Variable::new(0);
assert_eq!(func.dfg.num_block_params(block0), 0);
ssa.use_var(&mut func, x_var, I32, block0);
assert_eq!(func.dfg.num_block_params(block0), 0);
assert_eq!(
func.dfg.insts[func.layout.first_inst(block0).unwrap()].opcode(),
Opcode::Iconst
);
}
#[test]
fn undef_in_entry_sealed_after() {
// Use a var which has not been defined, but the block is not sealed
// until afterward. Before sealing, the SSA builder should insert an
// block param; after sealing, it should be removed.
let mut func = Function::new();
let mut ssa = SSABuilder::default();
let block0 = func.dfg.make_block();
ssa.declare_block(block0);
let x_var = Variable::new(0);
assert_eq!(func.dfg.num_block_params(block0), 0);
ssa.use_var(&mut func, x_var, I32, block0);
assert_eq!(func.dfg.num_block_params(block0), 1);
ssa.seal_block(block0, &mut func);
assert_eq!(func.dfg.num_block_params(block0), 0);
assert_eq!(
func.dfg.insts[func.layout.first_inst(block0).unwrap()].opcode(),
Opcode::Iconst
);
}
#[test]
fn unreachable_use() {
// Here is the pseudo-program we want to translate:
// block0:
// return;
// block1:
// brif x, block1, block1;
let mut func = Function::new();
let mut ssa = SSABuilder::default();
let block0 = func.dfg.make_block();
let block1 = func.dfg.make_block();
{
let mut cur = FuncCursor::new(&mut func);
cur.insert_block(block0);
cur.insert_block(block1);
}
// block0
ssa.declare_block(block0);
ssa.seal_block(block0, &mut func);
{
let mut cur = FuncCursor::new(&mut func).at_bottom(block0);
cur.ins().return_(&[]);
}
// block1
ssa.declare_block(block1);
{
let mut cur = FuncCursor::new(&mut func).at_bottom(block1);
let x_var = Variable::new(0);
let x_val = ssa.use_var(&mut cur.func, x_var, I32, block1).0;
let brif = cur.ins().brif(x_val, block1, &[], block1, &[]);
ssa.declare_block_predecessor(block1, brif);
}
ssa.seal_block(block1, &mut func);
let flags = settings::Flags::new(settings::builder());
match verify_function(&func, &flags) {
Ok(()) => {}
Err(_errors) => {
#[cfg(feature = "std")]
panic!("{}", _errors);
#[cfg(not(feature = "std"))]
panic!("function failed to verify");
}
}
}
#[test]
fn unreachable_use_with_multiple_preds() {
// Here is the pseudo-program we want to translate:
// block0:
// return;
// block1:
// brif x, block1, block2;
// block2:
// jump block1;
let mut func = Function::new();
let mut ssa = SSABuilder::default();
let block0 = func.dfg.make_block();
let block1 = func.dfg.make_block();
let block2 = func.dfg.make_block();
{
let mut cur = FuncCursor::new(&mut func);
cur.insert_block(block0);
cur.insert_block(block1);
cur.insert_block(block2);
}
// block0
ssa.declare_block(block0);
ssa.seal_block(block0, &mut func);
{
let mut cur = FuncCursor::new(&mut func).at_bottom(block0);
cur.ins().return_(&[]);
}
// block1
ssa.declare_block(block1);
let brif = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block1);
let x_var = Variable::new(0);
let x_val = ssa.use_var(&mut cur.func, x_var, I32, block1).0;
cur.ins().brif(x_val, block2, &[], block1, &[])
};
// block2
ssa.declare_block(block2);
ssa.declare_block_predecessor(block1, brif);
ssa.declare_block_predecessor(block2, brif);
ssa.seal_block(block2, &mut func);
let jump_block2_block1 = {
let mut cur = FuncCursor::new(&mut func).at_bottom(block2);
cur.ins().jump(block1, &[])
};
// seal block1
ssa.declare_block_predecessor(block1, jump_block2_block1);
ssa.seal_block(block1, &mut func);
let flags = settings::Flags::new(settings::builder());
match verify_function(&func, &flags) {
Ok(()) => {}
Err(_errors) => {
#[cfg(feature = "std")]
panic!("{}", _errors);
#[cfg(not(feature = "std"))]
panic!("function failed to verify");
}
}
}
#[test]
fn reassign_with_predecessor_loop_hangs() {
// Here is the pseudo-program we want to translate:
// block0:
// var0 = iconst 0
// return;
// block1:
// jump block2;
// block2:
// ; phantom use of var0
// var0 = iconst 1
// jump block1;
let mut func = Function::new();
let mut ssa = SSABuilder::default();
let block0 = func.dfg.make_block();
let block1 = func.dfg.make_block();
let block2 = func.dfg.make_block();
let var0 = Variable::new(0);
{
let mut cur = FuncCursor::new(&mut func);
for block in [block0, block1, block2] {
cur.insert_block(block);
ssa.declare_block(block);
}
}
// block0
{
let mut cur = FuncCursor::new(&mut func).at_bottom(block0);
let var0_iconst = cur.ins().iconst(I32, 0);
ssa.def_var(var0, var0_iconst, block0);
cur.ins().return_(&[]);
}
// block1
{
let mut cur = FuncCursor::new(&mut func).at_bottom(block1);
let jump = cur.ins().jump(block2, &[]);
ssa.declare_block_predecessor(block2, jump);
}
// block2
{
let mut cur = FuncCursor::new(&mut func).at_bottom(block2);
let _ = ssa.use_var(&mut cur.func, var0, I32, block2).0;
let var0_iconst = cur.ins().iconst(I32, 1);
ssa.def_var(var0, var0_iconst, block2);
let jump = cur.ins().jump(block1, &[]);
ssa.declare_block_predecessor(block1, jump);
}
// The sealing algorithm would enter a infinite loop here
ssa.seal_all_blocks(&mut func);
}
}