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machinst: Avoid a full instructions traversal of all the blocks when computing the final block ordering;

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This commit is contained in:
Benjamin Bouvier
2020-05-05 18:58:47 +02:00
parent 162fcd3d75
commit 1d90751ba9
3 changed files with 22 additions and 18 deletions
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22
cranelift/codegen/src/machinst/blockorder.rs
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@@ -1,7 +1,6 @@
//! Computation of basic block order in emitted code.
use crate::machinst::*;
use regalloc::{BlockIx, Function};
/// Simple reverse postorder-based block order emission.
///
@@ -10,15 +9,13 @@ use regalloc::{BlockIx, Function};
struct BlockRPO {
visited: Vec<bool>,
postorder: Vec<BlockIndex>,
deferred_last: Option<BlockIndex>,
}
impl BlockRPO {
fn new<I: VCodeInst>(vcode: &VCode<I>) -> BlockRPO {
BlockRPO {
visited: vec![false; vcode.num_blocks()],
postorder: vec![],
deferred_last: None,
postorder: Vec::with_capacity(vcode.num_blocks()),
}
}
@@ -29,22 +26,15 @@ impl BlockRPO {
self.visit(vcode, *succ);
}
}
for i in vcode.block_insns(BlockIx::new(block)) {
if vcode.get_insn(i).is_epilogue_placeholder() {
debug_assert!(self.deferred_last.is_none());
self.deferred_last = Some(block);
return;
}
if Some(block) != vcode.fallthrough_return_block {
self.postorder.push(block);
}
self.postorder.push(block);
}
fn rpo(self) -> Vec<BlockIndex> {
fn rpo<I: VCodeInst>(self, vcode: &VCode<I>) -> Vec<BlockIndex> {
let mut rpo = self.postorder;
rpo.reverse();
if let Some(block) = self.deferred_last {
if let Some(block) = vcode.fallthrough_return_block {
rpo.push(block);
}
rpo
@@ -55,5 +45,5 @@ impl BlockRPO {
pub fn compute_final_block_order<I: VCodeInst>(vcode: &VCode<I>) -> Vec<BlockIndex> {
let mut rpo = BlockRPO::new(vcode);
rpo.visit(vcode, vcode.entry());
rpo.rpo()
rpo.rpo(vcode)
}