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Add a workaround for the `TailDuplicator` compile time overhead

This commit is contained in:
DianQK 2024-02-28 22:54:37 +08:00
parent b5bd98d540
commit 2884230df2
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GPG Key ID: 46BDB1AC96C48912
1 changed files with 24 additions and 5 deletions
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29
compiler/rustc_mir_transform/src/uninhabited_enum_branching.rs
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@ -4,7 +4,8 @@ use crate::MirPass;
use rustc_data_structures::fx::FxHashSet;
use rustc_middle::mir::patch::MirPatch;
use rustc_middle::mir::{
BasicBlockData, Body, Local, Operand, Rvalue, StatementKind, TerminatorKind,
BasicBlock, BasicBlockData, BasicBlocks, Body, Local, Operand, Rvalue, StatementKind,
TerminatorKind,
};
use rustc_middle::ty::layout::TyAndLayout;
use rustc_middle::ty::{Ty, TyCtxt};
@ -118,9 +119,28 @@ impl<'tcx> MirPass<'tcx> for UninhabitedEnumBranching {
unreachable_targets.push(index);
}
}
let replace_otherwise_to_unreachable = allowed_variants.len() <= 1
&& !body.basic_blocks[targets.otherwise()].is_empty_unreachable();
let otherwise_is_empty_unreachable =
body.basic_blocks[targets.otherwise()].is_empty_unreachable();
// After resolving https://github.com/llvm/llvm-project/issues/78578,
// we can remove the limit on the number of successors.
fn check_successors(basic_blocks: &BasicBlocks<'_>, bb: BasicBlock) -> bool {
let mut successors = basic_blocks[bb].terminator().successors();
let Some(first_successor) = successors.next() else { return true };
if successors.next().is_some() {
return true;
}
if let TerminatorKind::SwitchInt { .. } =
&basic_blocks[first_successor].terminator().kind
{
return false;
};
true
}
let otherwise_is_last_variant = !otherwise_is_empty_unreachable
&& allowed_variants.len() == 1
&& check_successors(&body.basic_blocks, targets.otherwise());
let replace_otherwise_to_unreachable = otherwise_is_last_variant
|| !otherwise_is_empty_unreachable && allowed_variants.is_empty();
if unreachable_targets.is_empty() && !replace_otherwise_to_unreachable {
continue;
@ -129,7 +149,6 @@ impl<'tcx> MirPass<'tcx> for UninhabitedEnumBranching {
let unreachable_block = patch.unreachable_no_cleanup_block();
let mut targets = targets.clone();
if replace_otherwise_to_unreachable {
let otherwise_is_last_variant = !allowed_variants.is_empty();
if otherwise_is_last_variant {
#[allow(rustc::potential_query_instability)]
let last_variant = *allowed_variants.iter().next().unwrap();