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Move post-elaboration const-checking earlier in the pipeline
Instead we run `RemoveFalseEdges` and `RemoveUninitDrops` at the
appropriate time. The extra `SimplifyCfg` avoids visiting unreachable
blocks during `RemoveUninitDrops`.
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ecstatic-morse committed Dec 1, 2021
1 parent 3e0e8be commit 58c996c
Showing 1 changed file with 14 additions and 2 deletions.
16 changes: 14 additions & 2 deletions compiler/rustc_mir_transform/src/lib.rs
Expand Up @@ -77,7 +77,7 @@ mod simplify_try;
mod uninhabited_enum_branching;
mod unreachable_prop;

use rustc_const_eval::transform::check_consts;
use rustc_const_eval::transform::check_consts::{self, ConstCx};
use rustc_const_eval::transform::promote_consts;
use rustc_const_eval::transform::validate;
pub use rustc_const_eval::transform::MirPass;
Expand Down Expand Up @@ -447,8 +447,20 @@ fn mir_drops_elaborated_and_const_checked<'tcx>(
let (body, _) = tcx.mir_promoted(def);
let mut body = body.steal();

// IMPORTANT
remove_false_edges::RemoveFalseEdges.run_pass(tcx, &mut body);

// Do a little drop elaboration before const-checking if `const_precise_live_drops` is enabled.
//
// FIXME: Can't use `run_passes` for these, since `run_passes` SILENTLY DOES NOTHING IF THE MIR
// PHASE DOESN'T CHANGE.
if check_consts::post_drop_elaboration::checking_enabled(&ConstCx::new(tcx, &body)) {
simplify::SimplifyCfg::new("remove-false-edges").run_pass(tcx, &mut body);
remove_uninit_drops::RemoveUninitDrops.run_pass(tcx, &mut body);
check_consts::post_drop_elaboration::check_live_drops(tcx, &body);
}

run_post_borrowck_cleanup_passes(tcx, &mut body);
check_consts::post_drop_elaboration::check_live_drops(tcx, &body);
tcx.alloc_steal_mir(body)
}

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