//! A Dominator Tree represented as mappings of Ebbs to their immediate dominator.
use entity::EntityMap;
use flowgraph::{BasicBlock, ControlFlowGraph};
use ir::instructions::BranchInfo;
use ir::{Ebb, ExpandedProgramPoint, Function, Inst, Layout, ProgramOrder, Value};
use packed_option::PackedOption;
use std::cmp;
use std::cmp::Ordering;
use std::mem;
use std::vec::Vec;
use timing;
/// RPO numbers are not first assigned in a contiguous way but as multiples of STRIDE, to leave
/// room for modifications of the dominator tree.
const STRIDE: u32 = 4;
/// Special RPO numbers used during `compute_postorder`.
const DONE: u32 = 1;
const SEEN: u32 = 2;
/// Dominator tree node. We keep one of these per EBB.
#[derive(Clone, Default)]
struct DomNode {
/// Number of this node in a reverse post-order traversal of the CFG, starting from 1.
/// This number is monotonic in the reverse postorder but not contiguous, since we leave
/// holes for later localized modifications of the dominator tree.
/// Unreachable nodes get number 0, all others are positive.
rpo_number: u32,
/// The immediate dominator of this EBB, represented as the branch or jump instruction at the
/// end of the dominating basic block.
///
/// This is `None` for unreachable blocks and the entry block which doesn't have an immediate
/// dominator.
idom: PackedOption<Inst>,
}
/// The dominator tree for a single function.
pub struct DominatorTree {
nodes: EntityMap<Ebb, DomNode>,
/// CFG post-order of all reachable EBBs.
postorder: Vec<Ebb>,
/// Scratch memory used by `compute_postorder()`.
stack: Vec<Ebb>,
valid: bool,
}
/// Methods for querying the dominator tree.
impl DominatorTree {
/// Is `ebb` reachable from the entry block?
pub fn is_reachable(&self, ebb: Ebb) -> bool {
self.nodes[ebb].rpo_number != 0
}
/// Get the CFG post-order of EBBs that was used to compute the dominator tree.
///
/// Note that this post-order is not updated automatically when the CFG is modified. It is
/// computed from scratch and cached by `compute()`.
pub fn cfg_postorder(&self) -> &[Ebb] {
debug_assert!(self.is_valid());
&self.postorder
}
/// Returns the immediate dominator of `ebb`.
///
/// The immediate dominator of an extended basic block is a basic block which we represent by
/// the branch or jump instruction at the end of the basic block. This does not have to be the
/// terminator of its EBB.
///
/// A branch or jump is said to *dominate* `ebb` if all control flow paths from the function
/// entry to `ebb` must go through the branch.
///
/// The *immediate dominator* is the dominator that is closest to `ebb`. All other dominators
/// also dominate the immediate dominator.
///
/// This returns `None` if `ebb` is not reachable from the entry EBB, or if it is the entry EBB
/// which has no dominators.
pub fn idom(&self, ebb: Ebb) -> Option<Inst> {
self.nodes[ebb].idom.into()
}
/// Compare two EBBs relative to the reverse post-order.
fn rpo_cmp_ebb(&self, a: Ebb, b: Ebb) -> Ordering {
self.nodes[a].rpo_number.cmp(&self.nodes[b].rpo_number)
}
/// Compare two program points relative to a reverse post-order traversal of the control-flow
/// graph.
///
/// Return `Ordering::Less` if `a` comes before `b` in the RPO.
///
/// If `a` and `b` belong to the same EBB, compare their relative position in the EBB.
pub fn rpo_cmp<A, B>(&self, a: A, b: B, layout: &Layout) -> Ordering
where
A: Into<ExpandedProgramPoint>,
B: Into<ExpandedProgramPoint>,
{
let a = a.into();
let b = b.into();
self.rpo_cmp_ebb(layout.pp_ebb(a), layout.pp_ebb(b))
.then(layout.cmp(a, b))
}
/// Returns `true` if `a` dominates `b`.
///
/// This means that every control-flow path from the function entry to `b` must go through `a`.
///
/// Dominance is ill defined for unreachable blocks. This function can always determine
/// dominance for instructions in the same EBB, but otherwise returns `false` if either block
/// is unreachable.
///
/// An instruction is considered to dominate itself.
pub fn dominates<A, B>(&self, a: A, b: B, layout: &Layout) -> bool
where
A: Into<ExpandedProgramPoint>,
B: Into<ExpandedProgramPoint>,
{
let a = a.into();
let b = b.into();
match a {
ExpandedProgramPoint::Ebb(ebb_a) => {
a == b || self.last_dominator(ebb_a, b, layout).is_some()
}
ExpandedProgramPoint::Inst(inst_a) => {
let ebb_a = layout.inst_ebb(inst_a).expect("Instruction not in layout.");
match self.last_dominator(ebb_a, b, layout) {
Some(last) => layout.cmp(inst_a, last) != Ordering::Greater,
None => false,
}
}
}
}
/// Find the last instruction in `a` that dominates `b`.
/// If no instructions in `a` dominate `b`, return `None`.
pub fn last_dominator<B>(&self, a: Ebb, b: B, layout: &Layout) -> Option<Inst>
where
B: Into<ExpandedProgramPoint>,
{
let (mut ebb_b, mut inst_b) = match b.into() {
ExpandedProgramPoint::Ebb(ebb) => (ebb, None),
ExpandedProgramPoint::Inst(inst) => (
layout.inst_ebb(inst).expect("Instruction not in layout."),
Some(inst),
),
};
let rpo_a = self.nodes[a].rpo_number;
// Run a finger up the dominator tree from b until we see a.
// Do nothing if b is unreachable.
while rpo_a < self.nodes[ebb_b].rpo_number {
let idom = match self.idom(ebb_b) {
Some(idom) => idom,
None => return None, // a is unreachable, so we climbed past the entry
};
ebb_b = layout.inst_ebb(idom).expect("Dominator got removed.");
inst_b = Some(idom);
}
if a == ebb_b {
inst_b
} else {
None
}
}
/// Compute the common dominator of two basic blocks.
///
/// Both basic blocks are assumed to be reachable.
pub fn common_dominator(
&self,
mut a: BasicBlock,
mut b: BasicBlock,
layout: &Layout,
) -> BasicBlock {
loop {
match self.rpo_cmp_ebb(a.0, b.0) {
Ordering::Less => {
// `a` comes before `b` in the RPO. Move `b` up.
let idom = self.nodes[b.0].idom.expect("Unreachable basic block?");
b = (
layout.inst_ebb(idom).expect("Dangling idom instruction"),
idom,
);
}
Ordering::Greater => {
// `b` comes before `a` in the RPO. Move `a` up.
let idom = self.nodes[a.0].idom.expect("Unreachable basic block?");
a = (
layout.inst_ebb(idom).expect("Dangling idom instruction"),
idom,
);
}
Ordering::Equal => break,
}
}
debug_assert_eq!(a.0, b.0, "Unreachable block passed to common_dominator?");
// We're in the same EBB. The common dominator is the earlier instruction.
if layout.cmp(a.1, b.1) == Ordering::Less {
a
} else {
b
}
}
}
impl DominatorTree {
/// Allocate a new blank dominator tree. Use `compute` to compute the dominator tree for a
/// function.
pub fn new() -> Self {
Self {
nodes: EntityMap::new(),
postorder: Vec::new(),
stack: Vec::new(),
valid: false,
}
}
/// Allocate and compute a dominator tree.
pub fn with_function(func: &Function, cfg: &ControlFlowGraph) -> Self {
let mut domtree = Self::new();
domtree.compute(func, cfg);
domtree
}
/// Reset and compute a CFG post-order and dominator tree.
pub fn compute(&mut self, func: &Function, cfg: &ControlFlowGraph) {
let _tt = timing::domtree();
debug_assert!(cfg.is_valid());
self.compute_postorder(func);
self.compute_domtree(func, cfg);
self.valid = true;
}
/// Clear the data structures used to represent the dominator tree. This will leave the tree in
/// a state where `is_valid()` returns false.
pub fn clear(&mut self) {
self.nodes.clear();
self.postorder.clear();
debug_assert!(self.stack.is_empty());
self.valid = false;
}
/// Check if the dominator tree is in a valid state.
///
/// Note that this doesn't perform any kind of validity checks. It simply checks if the
/// `compute()` method has been called since the last `clear()`. It does not check that the
/// dominator tree is consistent with the CFG.
pub fn is_valid(&self) -> bool {
self.valid
}
/// Reset all internal data structures and compute a post-order of the control flow graph.
///
/// This leaves `rpo_number == 1` for all reachable EBBs, 0 for unreachable ones.
fn compute_postorder(&mut self, func: &Function) {
self.clear();
self.nodes.resize(func.dfg.num_ebbs());
// This algorithm is a depth first traversal (DFT) of the control flow graph, computing a
// post-order of the EBBs that are reachable form the entry block. A DFT post-order is not
// unique. The specific order we get is controlled by two factors:
//
// 1. The order each node's children are visited, and
// 2. The method used for pruning graph edges to get a tree.
//
// There are two ways of viewing the CFG as a graph:
//
// 1. Each EBB is a node, with outgoing edges for all the branches in the EBB>
// 2. Each basic block is a node, with outgoing edges for the single branch at the end of
// the BB. (An EBB is a linear sequence of basic blocks).
//
// The first graph is a contraction of the second one. We want to compute an EBB post-order
// that is compatible both graph interpretations. That is, if you compute a BB post-order
// and then remove those BBs that do not correspond to EBB headers, you get a post-order of
// the EBB graph.
//
// Node child order:
//
// In the BB graph, we always go down the fall-through path first and follow the branch
// destination second.
//
// In the EBB graph, this is equivalent to visiting EBB successors in a bottom-up
// order, starting from the destination of the EBB's terminating jump, ending at the
// destination of the first branch in the EBB.
//
// Edge pruning:
//
// In the BB graph, we keep an edge to an EBB the first time we visit the *source* side
// of the edge. Any subsequent edges to the same EBB are pruned.
//
// The equivalent tree is reached in the EBB graph by keeping the first edge to an EBB
// in a top-down traversal of the successors. (And then visiting edges in a bottom-up
// order).
//
// This pruning method makes it possible to compute the DFT without storing lots of
// information about the progress through an EBB.
// During this algorithm only, use `rpo_number` to hold the following state:
//
// 0: EBB has not yet been reached in the pre-order.
// SEEN: EBB has been pushed on the stack but successors not yet pushed.
// DONE: Successors pushed.
match func.layout.entry_block() {
Some(ebb) => {
self.stack.push(ebb);
self.nodes[ebb].rpo_number = SEEN;
}
None => return,
}
while let Some(ebb) = self.stack.pop() {
match self.nodes[ebb].rpo_number {
SEEN => {
// This is the first time we pop the EBB, so we need to scan its successors and
// then revisit it.
self.nodes[ebb].rpo_number = DONE;
self.stack.push(ebb);
self.push_successors(func, ebb);
}
DONE => {
// This is the second time we pop the EBB, so all successors have been
// processed.
self.postorder.push(ebb);
}
_ => unreachable!(),
}
}
}
/// Push `ebb` successors onto `self.stack`, filtering out those that have already been seen.
///
/// The successors are pushed in program order which is important to get a split-invariant
/// post-order. Split-invariant means that if an EBB is split in two, we get the same
/// post-order except for the insertion of the new EBB header at the split point.
fn push_successors(&mut self, func: &Function, ebb: Ebb) {
for inst in func.layout.ebb_insts(ebb) {
match func.dfg.analyze_branch(inst) {
BranchInfo::SingleDest(succ, _) => {
if self.nodes[succ].rpo_number == 0 {
self.nodes[succ].rpo_number = SEEN;
self.stack.push(succ);
}
}
BranchInfo::Table(jt) => {
for (_, succ) in func.jump_tables[jt].entries() {
if self.nodes[succ].rpo_number == 0 {
self.nodes[succ].rpo_number = SEEN;
self.stack.push(succ);
}
}
}
BranchInfo::NotABranch => {}
}
}
}
/// Build a dominator tree from a control flow graph using Keith D. Cooper's
/// "Simple, Fast Dominator Algorithm."
fn compute_domtree(&mut self, func: &Function, cfg: &ControlFlowGraph) {
// During this algorithm, `rpo_number` has the following values:
//
// 0: EBB is not reachable.
// 1: EBB is reachable, but has not yet been visited during the first pass. This is set by
// `compute_postorder`.
// 2+: EBB is reachable and has an assigned RPO number.
// We'll be iterating over a reverse post-order of the CFG, skipping the entry block.
let (entry_block, postorder) = match self.postorder.as_slice().split_last() {
Some((&eb, rest)) => (eb, rest),
None => return,
};
debug_assert_eq!(Some(entry_block), func.layout.entry_block());
// Do a first pass where we assign RPO numbers to all reachable nodes.
self.nodes[entry_block].rpo_number = 2 * STRIDE;
for (rpo_idx, &ebb) in postorder.iter().rev().enumerate() {
// Update the current node and give it an RPO number.
// The entry block got 2, the rest start at 3 by multiples of STRIDE to leave
// room for future dominator tree modifications.
//
// Since `compute_idom` will only look at nodes with an assigned RPO number, the
// function will never see an uninitialized predecessor.
//
// Due to the nature of the post-order traversal, every node we visit will have at
// least one predecessor that has previously been visited during this RPO.
self.nodes[ebb] = DomNode {
idom: self.compute_idom(ebb, cfg, &func.layout).into(),
rpo_number: (rpo_idx as u32 + 3) * STRIDE,
}
}
// Now that we have RPO numbers for everything and initial immediate dominator estimates,
// iterate until convergence.
//
// If the function is free of irreducible control flow, this will exit after one iteration.
let mut changed = true;
while changed {
changed = false;
for &ebb in postorder.iter().rev() {
let idom = self.compute_idom(ebb, cfg, &func.layout).into();
if self.nodes[ebb].idom != idom {
self.nodes[ebb].idom = idom;
changed = true;
}
}
}
}
// Compute the immediate dominator for `ebb` using the current `idom` states for the reachable
// nodes.
fn compute_idom(&self, ebb: Ebb, cfg: &ControlFlowGraph, layout: &Layout) -> Inst {
// Get an iterator with just the reachable, already visited predecessors to `ebb`.
// Note that during the first pass, `rpo_number` is 1 for reachable blocks that haven't
// been visited yet, 0 for unreachable blocks.
let mut reachable_preds = cfg.pred_iter(ebb)
.filter(|&(pred, _)| self.nodes[pred].rpo_number > 1);
// The RPO must visit at least one predecessor before this node.
let mut idom = reachable_preds
.next()
.expect("EBB node must have one reachable predecessor");
for pred in reachable_preds {
idom = self.common_dominator(idom, pred, layout);
}
idom.1
}
}
impl DominatorTree {
/// When splitting an `Ebb` using `Layout::split_ebb`, you can use this method to update
/// the dominator tree locally rather than recomputing it.
///
/// `old_ebb` is the `Ebb` before splitting, and `new_ebb` is the `Ebb` which now contains
/// the second half of `old_ebb`. `split_jump_inst` is the terminator jump instruction of
/// `old_ebb` that points to `new_ebb`.
pub fn recompute_split_ebb(&mut self, old_ebb: Ebb, new_ebb: Ebb, split_jump_inst: Inst) {
if !self.is_reachable(old_ebb) {
// old_ebb is unreachable, it stays so and new_ebb is unreachable too
self.nodes[new_ebb] = Default::default();
return;
}
// We use the RPO comparison on the postorder list so we invert the operands of the
// comparison
let old_ebb_postorder_index = self.postorder
.as_slice()
.binary_search_by(|probe| self.rpo_cmp_ebb(old_ebb, *probe))
.expect("the old ebb is not declared to the dominator tree");
let new_ebb_rpo = self.insert_after_rpo(old_ebb, old_ebb_postorder_index, new_ebb);
self.nodes[new_ebb] = DomNode {
rpo_number: new_ebb_rpo,
idom: Some(split_jump_inst).into(),
};
}
// Insert new_ebb just after ebb in the RPO. This function checks
// if there is a gap in rpo numbers; if yes it returns the number in the gap and if
// not it renumbers.
fn insert_after_rpo(&mut self, ebb: Ebb, ebb_postorder_index: usize, new_ebb: Ebb) -> u32 {
let ebb_rpo_number = self.nodes[ebb].rpo_number;
let inserted_rpo_number = ebb_rpo_number + 1;
// If there is no gaps in RPo numbers to insert this new number, we iterate
// forward in RPO numbers and backwards in the postorder list of EBBs, renumbering the Ebbs
// until we find a gap
for (¤t_ebb, current_rpo) in self.postorder[0..ebb_postorder_index]
.iter()
.rev()
.zip(inserted_rpo_number + 1..)
{
if self.nodes[current_ebb].rpo_number < current_rpo {
// There is no gap, we renumber
self.nodes[current_ebb].rpo_number = current_rpo;
} else {
// There is a gap, we stop the renumbering and exit
break;
}
}
// TODO: insert in constant time?
self.postorder.insert(ebb_postorder_index, new_ebb);
inserted_rpo_number
}
}
/// Optional pre-order information that can be computed for a dominator tree.
///
/// This data structure is computed from a `DominatorTree` and provides:
///
/// - A forward traversable dominator tree through the `children()` iterator.
/// - An ordering of EBBs according to a dominator tree pre-order.
/// - Constant time dominance checks at the EBB granularity.
///
/// The information in this auxillary data structure is not easy to update when the control flow
/// graph changes, which is why it is kept separate.
pub struct DominatorTreePreorder {
nodes: EntityMap<Ebb, ExtraNode>,
// Scratch memory used by `compute_postorder()`.
stack: Vec<Ebb>,
}
#[derive(Default, Clone)]
struct ExtraNode {
/// First child node in the domtree.
child: PackedOption<Ebb>,
/// Next sibling node in the domtree. This linked list is ordered according to the CFG RPO.
sibling: PackedOption<Ebb>,
/// Sequence number for this node in a pre-order traversal of the dominator tree.
/// Unreachable blocks have number 0, the entry block is 1.
pre_number: u32,
/// Maximum `pre_number` for the sub-tree of the dominator tree that is rooted at this node.
/// This is always >= `pre_number`.
pre_max: u32,
}
/// Creating and computing the dominator tree pre-order.
impl DominatorTreePreorder {
/// Create a new blank `DominatorTreePreorder`.
pub fn new() -> Self {
Self {
nodes: EntityMap::new(),
stack: Vec::new(),
}
}
/// Recompute this data structure to match `domtree`.
pub fn compute(&mut self, domtree: &DominatorTree, layout: &Layout) {
self.nodes.clear();
debug_assert_eq!(self.stack.len(), 0);
// Step 1: Populate the child and sibling links.
//
// By following the CFG post-order and pushing to the front of the lists, we make sure that
// sibling lists are ordered according to the CFG reverse post-order.
for &ebb in domtree.cfg_postorder() {
if let Some(idom_inst) = domtree.idom(ebb) {
let idom = layout.pp_ebb(idom_inst);
let sib = mem::replace(&mut self.nodes[idom].child, ebb.into());
self.nodes[ebb].sibling = sib;
} else {
// The only EBB without an immediate dominator is the entry.
self.stack.push(ebb);
}
}
// Step 2. Assign pre-order numbers from a DFS of the dominator tree.
debug_assert!(self.stack.len() <= 1);
let mut n = 0;
while let Some(ebb) = self.stack.pop() {
n += 1;
let node = &mut self.nodes[ebb];
node.pre_number = n;
node.pre_max = n;
if let Some(n) = node.sibling.expand() {
self.stack.push(n);
}
if let Some(n) = node.child.expand() {
self.stack.push(n);
}
}
// Step 3. Propagate the `pre_max` numbers up the tree.
// The CFG post-order is topologically ordered w.r.t. dominance so a node comes after all
// its dominator tree children.
for &ebb in domtree.cfg_postorder() {
if let Some(idom_inst) = domtree.idom(ebb) {
let idom = layout.pp_ebb(idom_inst);
let pre_max = cmp::max(self.nodes[ebb].pre_max, self.nodes[idom].pre_max);
self.nodes[idom].pre_max = pre_max;
}
}
}
}
/// An iterator that enumerates the direct children of an EBB in the dominator tree.
pub struct ChildIter<'a> {
dtpo: &'a DominatorTreePreorder,
next: PackedOption<Ebb>,
}
impl<'a> Iterator for ChildIter<'a> {
type Item = Ebb;
fn next(&mut self) -> Option<Ebb> {
let n = self.next.expand();
if let Some(ebb) = n {
self.next = self.dtpo.nodes[ebb].sibling;
}
n
}
}
/// Query interface for the dominator tree pre-order.
impl DominatorTreePreorder {
/// Get an iterator over the direct children of `ebb` in the dominator tree.
///
/// These are the EBB's whose immediate dominator is an instruction in `ebb`, ordered according
/// to the CFG reverse post-order.
pub fn children(&self, ebb: Ebb) -> ChildIter {
ChildIter {
dtpo: self,
next: self.nodes[ebb].child,
}
}
/// Fast, constant time dominance check with EBB granularity.
///
/// This computes the same result as `domtree.dominates(a, b)`, but in guaranteed fast constant
/// time. This is less general than the `DominatorTree` method because it only works with EBB
/// program points.
///
/// An EBB is considered to dominate itself.
pub fn dominates(&self, a: Ebb, b: Ebb) -> bool {
let na = &self.nodes[a];
let nb = &self.nodes[b];
na.pre_number <= nb.pre_number && na.pre_max >= nb.pre_max
}
/// Compare two EBBs according to the dominator pre-order.
pub fn pre_cmp_ebb(&self, a: Ebb, b: Ebb) -> Ordering {
self.nodes[a].pre_number.cmp(&self.nodes[b].pre_number)
}
/// Compare two program points according to the dominator tree pre-order.
///
/// This ordering of program points have the property that given a program point, pp, all the
/// program points dominated by pp follow immediately and contiguously after pp in the order.
pub fn pre_cmp<A, B>(&self, a: A, b: B, layout: &Layout) -> Ordering
where
A: Into<ExpandedProgramPoint>,
B: Into<ExpandedProgramPoint>,
{
let a = a.into();
let b = b.into();
self.pre_cmp_ebb(layout.pp_ebb(a), layout.pp_ebb(b))
.then(layout.cmp(a, b))
}
/// Compare two value defs according to the dominator tree pre-order.
///
/// Two values defined at the same program point are compared according to their parameter or
/// result order.
///
/// This is a total ordering of the values in the function.
pub fn pre_cmp_def(&self, a: Value, b: Value, func: &Function) -> Ordering {
let da = func.dfg.value_def(a);
let db = func.dfg.value_def(b);
self.pre_cmp(da, db, &func.layout)
.then_with(|| da.num().cmp(&db.num()))
}
}
#[cfg(test)]
mod test {
use super::*;
use cursor::{Cursor, FuncCursor};
use flowgraph::ControlFlowGraph;
use ir::types::*;
use ir::{Function, InstBuilder, TrapCode};
use settings;
use verifier::verify_context;
#[test]
fn empty() {
let func = Function::new();
let cfg = ControlFlowGraph::with_function(&func);
debug_assert!(cfg.is_valid());
let dtree = DominatorTree::with_function(&func, &cfg);
assert_eq!(0, dtree.nodes.keys().count());
assert_eq!(dtree.cfg_postorder(), &[]);
let mut dtpo = DominatorTreePreorder::new();
dtpo.compute(&dtree, &func.layout);
}
#[test]
fn unreachable_node() {
let mut func = Function::new();
let ebb0 = func.dfg.make_ebb();
let v0 = func.dfg.append_ebb_param(ebb0, I32);
let ebb1 = func.dfg.make_ebb();
let ebb2 = func.dfg.make_ebb();
let mut cur = FuncCursor::new(&mut func);
cur.insert_ebb(ebb0);
cur.ins().brnz(v0, ebb2, &[]);
cur.ins().trap(TrapCode::User(0));
cur.insert_ebb(ebb1);
let v1 = cur.ins().iconst(I32, 1);
let v2 = cur.ins().iadd(v0, v1);
cur.ins().jump(ebb0, &[v2]);
cur.insert_ebb(ebb2);
cur.ins().return_(&[v0]);
let cfg = ControlFlowGraph::with_function(cur.func);
let dt = DominatorTree::with_function(cur.func, &cfg);
// Fall-through-first, prune-at-source DFT:
//
// ebb0 {
// brnz ebb2 {
// trap
// ebb2 {
// return
// } ebb2
// } ebb0
assert_eq!(dt.cfg_postorder(), &[ebb2, ebb0]);
let v2_def = cur.func.dfg.value_def(v2).unwrap_inst();
assert!(!dt.dominates(v2_def, ebb0, &cur.func.layout));
assert!(!dt.dominates(ebb0, v2_def, &cur.func.layout));
let mut dtpo = DominatorTreePreorder::new();
dtpo.compute(&dt, &cur.func.layout);
assert!(dtpo.dominates(ebb0, ebb0));
assert!(!dtpo.dominates(ebb0, ebb1));
assert!(dtpo.dominates(ebb0, ebb2));
assert!(!dtpo.dominates(ebb1, ebb0));
assert!(dtpo.dominates(ebb1, ebb1));
assert!(!dtpo.dominates(ebb1, ebb2));
assert!(!dtpo.dominates(ebb2, ebb0));
assert!(!dtpo.dominates(ebb2, ebb1));
assert!(dtpo.dominates(ebb2, ebb2));
}
#[test]
fn non_zero_entry_block() {
let mut func = Function::new();
let ebb0 = func.dfg.make_ebb();
let ebb1 = func.dfg.make_ebb();
let ebb2 = func.dfg.make_ebb();
let ebb3 = func.dfg.make_ebb();
let cond = func.dfg.append_ebb_param(ebb3, I32);
let mut cur = FuncCursor::new(&mut func);
cur.insert_ebb(ebb3);
let jmp_ebb3_ebb1 = cur.ins().jump(ebb1, &[]);
cur.insert_ebb(ebb1);
let br_ebb1_ebb0 = cur.ins().brnz(cond, ebb0, &[]);
let jmp_ebb1_ebb2 = cur.ins().jump(ebb2, &[]);
cur.insert_ebb(ebb2);
cur.ins().jump(ebb0, &[]);
cur.insert_ebb(ebb0);
let cfg = ControlFlowGraph::with_function(cur.func);
let dt = DominatorTree::with_function(cur.func, &cfg);
// Fall-through-first, prune-at-source DFT:
//
// ebb3 {
// ebb3:jump ebb1 {
// ebb1 {
// ebb1:brnz ebb0 {
// ebb1:jump ebb2 {
// ebb2 {
// ebb2:jump ebb0 (seen)
// } ebb2
// } ebb1:jump ebb2
// ebb0 {
// } ebb0
// } ebb1:brnz ebb0
// } ebb1
// } ebb3:jump ebb1
// } ebb3
assert_eq!(dt.cfg_postorder(), &[ebb2, ebb0, ebb1, ebb3]);
assert_eq!(cur.func.layout.entry_block().unwrap(), ebb3);
assert_eq!(dt.idom(ebb3), None);
assert_eq!(dt.idom(ebb1).unwrap(), jmp_ebb3_ebb1);
assert_eq!(dt.idom(ebb2).unwrap(), jmp_ebb1_ebb2);
assert_eq!(dt.idom(ebb0).unwrap(), br_ebb1_ebb0);
assert!(dt.dominates(br_ebb1_ebb0, br_ebb1_ebb0, &cur.func.layout));
assert!(!dt.dominates(br_ebb1_ebb0, jmp_ebb3_ebb1, &cur.func.layout));
assert!(dt.dominates(jmp_ebb3_ebb1, br_ebb1_ebb0, &cur.func.layout));
assert_eq!(dt.rpo_cmp(ebb3, ebb3, &cur.func.layout), Ordering::Equal);
assert_eq!(dt.rpo_cmp(ebb3, ebb1, &cur.func.layout), Ordering::Less);
assert_eq!(
dt.rpo_cmp(ebb3, jmp_ebb3_ebb1, &cur.func.layout),
Ordering::Less
);
assert_eq!(
dt.rpo_cmp(jmp_ebb3_ebb1, jmp_ebb1_ebb2, &cur.func.layout),
Ordering::Less
);
}
#[test]
fn backwards_layout() {
let mut func = Function::new();
let ebb0 = func.dfg.make_ebb();
let ebb1 = func.dfg.make_ebb();
let ebb2 = func.dfg.make_ebb();
let mut cur = FuncCursor::new(&mut func);
cur.insert_ebb(ebb0);
let jmp02 = cur.ins().jump(ebb2, &[]);
cur.insert_ebb(ebb1);
let trap = cur.ins().trap(TrapCode::User(5));
cur.insert_ebb(ebb2);
let jmp21 = cur.ins().jump(ebb1, &[]);
let cfg = ControlFlowGraph::with_function(cur.func);
let dt = DominatorTree::with_function(cur.func, &cfg);
assert_eq!(cur.func.layout.entry_block(), Some(ebb0));
assert_eq!(dt.idom(ebb0), None);
assert_eq!(dt.idom(ebb1), Some(jmp21));
assert_eq!(dt.idom(ebb2), Some(jmp02));
assert!(dt.dominates(ebb0, ebb0, &cur.func.layout));
assert!(dt.dominates(ebb0, jmp02, &cur.func.layout));
assert!(dt.dominates(ebb0, ebb1, &cur.func.layout));
assert!(dt.dominates(ebb0, trap, &cur.func.layout));
assert!(dt.dominates(ebb0, ebb2, &cur.func.layout));
assert!(dt.dominates(ebb0, jmp21, &cur.func.layout));
assert!(!dt.dominates(jmp02, ebb0, &cur.func.layout));
assert!(dt.dominates(jmp02, jmp02, &cur.func.layout));
assert!(dt.dominates(jmp02, ebb1, &cur.func.layout));
assert!(dt.dominates(jmp02, trap, &cur.func.layout));
assert!(dt.dominates(jmp02, ebb2, &cur.func.layout));
assert!(dt.dominates(jmp02, jmp21, &cur.func.layout));
assert!(!dt.dominates(ebb1, ebb0, &cur.func.layout));
assert!(!dt.dominates(ebb1, jmp02, &cur.func.layout));
assert!(dt.dominates(ebb1, ebb1, &cur.func.layout));
assert!(dt.dominates(ebb1, trap, &cur.func.layout));
assert!(!dt.dominates(ebb1, ebb2, &cur.func.layout));
assert!(!dt.dominates(ebb1, jmp21, &cur.func.layout));
assert!(!dt.dominates(trap, ebb0, &cur.func.layout));
assert!(!dt.dominates(trap, jmp02, &cur.func.layout));
assert!(!dt.dominates(trap, ebb1, &cur.func.layout));
assert!(dt.dominates(trap, trap, &cur.func.layout));
assert!(!dt.dominates(trap, ebb2, &cur.func.layout));
assert!(!dt.dominates(trap, jmp21, &cur.func.layout));
assert!(!dt.dominates(ebb2, ebb0, &cur.func.layout));
assert!(!dt.dominates(ebb2, jmp02, &cur.func.layout));
assert!(dt.dominates(ebb2, ebb1, &cur.func.layout));
assert!(dt.dominates(ebb2, trap, &cur.func.layout));
assert!(dt.dominates(ebb2, ebb2, &cur.func.layout));
assert!(dt.dominates(ebb2, jmp21, &cur.func.layout));
assert!(!dt.dominates(jmp21, ebb0, &cur.func.layout));
assert!(!dt.dominates(jmp21, jmp02, &cur.func.layout));
assert!(dt.dominates(jmp21, ebb1, &cur.func.layout));
assert!(dt.dominates(jmp21, trap, &cur.func.layout));
assert!(!dt.dominates(jmp21, ebb2, &cur.func.layout));
assert!(dt.dominates(jmp21, jmp21, &cur.func.layout));
}
#[test]
fn renumbering() {
let mut func = Function::new();
let entry = func.dfg.make_ebb();
let ebb0 = func.dfg.make_ebb();
let ebb100 = func.dfg.make_ebb();
let mut cur = FuncCursor::new(&mut func);
cur.insert_ebb(entry);
cur.ins().jump(ebb0, &[]);
cur.insert_ebb(ebb0);
let cond = cur.ins().iconst(I32, 0);
let inst2 = cur.ins().brz(cond, ebb0, &[]);
let inst3 = cur.ins().brz(cond, ebb0, &[]);
let inst4 = cur.ins().brz(cond, ebb0, &[]);
let inst5 = cur.ins().brz(cond, ebb0, &[]);
cur.ins().jump(ebb100, &[]);
cur.insert_ebb(ebb100);
cur.ins().return_(&[]);
let mut cfg = ControlFlowGraph::with_function(cur.func);
let mut dt = DominatorTree::with_function(cur.func, &cfg);
let ebb1 = cur.func.dfg.make_ebb();
cur.func.layout.split_ebb(ebb1, inst2);
cur.goto_bottom(ebb0);
let middle_jump_inst = cur.ins().jump(ebb1, &[]);
dt.recompute_split_ebb(ebb0, ebb1, middle_jump_inst);
let ebb2 = cur.func.dfg.make_ebb();
cur.func.layout.split_ebb(ebb2, inst3);
cur.goto_bottom(ebb1);
let middle_jump_inst = cur.ins().jump(ebb2, &[]);
dt.recompute_split_ebb(ebb1, ebb2, middle_jump_inst);
let ebb3 = cur.func.dfg.make_ebb();
cur.func.layout.split_ebb(ebb3, inst4);
cur.goto_bottom(ebb2);
let middle_jump_inst = cur.ins().jump(ebb3, &[]);
dt.recompute_split_ebb(ebb2, ebb3, middle_jump_inst);
let ebb4 = cur.func.dfg.make_ebb();
cur.func.layout.split_ebb(ebb4, inst5);
cur.goto_bottom(ebb3);
let middle_jump_inst = cur.ins().jump(ebb4, &[]);
dt.recompute_split_ebb(ebb3, ebb4, middle_jump_inst);
cfg.compute(cur.func);
let flags = settings::Flags::new(settings::builder());
verify_context(cur.func, &cfg, &dt, &flags).unwrap();
}
}