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Insert split-edge of conditional branches before the destination.

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This commit is contained in:
Nicolas B. Pierron
2019-10-01 14:45:08 +02:00
committed by Nicolas B. Pierron
parent 093b3b3426
commit e0005f1e6c
5 changed files with 32 additions and 52 deletions
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37
cranelift/codegen/src/regalloc/branch_splitting.rs
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@@ -22,7 +22,6 @@ pub fn run(
) {
let mut ctx = Context {
has_new_blocks: false,
has_fallthrough_return: None,
cur: EncCursor::new(func, isa),
domtree,
topo,
@@ -35,12 +34,6 @@ struct Context<'a> {
/// True if new blocks were inserted.
has_new_blocks: bool,
/// Record whether newly inserted empty blocks should be inserted last, or before the last, to
/// avoid disturbing the expected control flow of `fallthroug_return` statements.
///
/// This value is computed when needed. The Option wraps the computed value if any.
has_fallthrough_return: Option<bool>,
/// Current instruction as well as reference to function and ISA.
cur: EncCursor<'a>,
@@ -89,7 +82,13 @@ impl<'a> Context<'a> {
// If there are any parameters, split the edge.
if self.should_split_edge(target) {
// Create the block the branch will jump to.
let new_ebb = self.make_empty_ebb();
let new_ebb = self.cur.func.dfg.make_ebb();
// Insert the new block before the destination, such that it can fallthrough in the
// target block.
assert_ne!(Some(target), self.cur.layout().entry_block());
self.cur.layout_mut().insert_ebb(new_ebb, target);
self.has_new_blocks = true;
// Extract the arguments of the branch instruction, split the Ebb parameters and the
// branch arguments
@@ -157,28 +156,6 @@ impl<'a> Context<'a> {
}
}
// A new ebb must be inserted before the last ebb because the last ebb may have a
// fallthrough_return and can't have anything after it.
fn make_empty_ebb(&mut self) -> Ebb {
let last_ebb = self.cur.layout().last_ebb().unwrap();
if self.has_fallthrough_return == None {
let last_inst = self.cur.layout().last_inst(last_ebb).unwrap();
self.has_fallthrough_return =
Some(self.cur.func.dfg[last_inst].opcode() == Opcode::FallthroughReturn);
}
let new_ebb = self.cur.func.dfg.make_ebb();
if self.has_fallthrough_return == Some(true) {
// Insert before the last block which has a fallthrough_return
// instruction.
self.cur.layout_mut().insert_ebb(new_ebb, last_ebb);
} else {
// Insert after the last block.
self.cur.layout_mut().insert_ebb_after(new_ebb, last_ebb);
}
self.has_new_blocks = true;
new_ebb
}
/// Returns whether we should introduce a new branch.
fn should_split_edge(&self, target: Ebb) -> bool {
// We should split the edge if the target has any parameters.