From 508b803c44e4df10fe189e8d1ae3a551ade9b2da Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tomasz=20Mi=C4=85sko?= <tomasz.miasko@gmail.com>
Date: Wed, 5 Mar 2025 23:36:47 +0100
Subject: [PATCH 1/2] Remove start block special case
Edges to the start block are invalid. The special case is unnecessary.
---
compiler/rustc_mir_transform/src/add_call_guards.rs | 1 -
1 file changed, 1 deletion(-)
diff --git a/compiler/rustc_mir_transform/src/add_call_guards.rs b/compiler/rustc_mir_transform/src/add_call_guards.rs
index 55694cacd92e0..f9e757dda431c 100644
--- a/compiler/rustc_mir_transform/src/add_call_guards.rs
+++ b/compiler/rustc_mir_transform/src/add_call_guards.rs
@@ -34,7 +34,6 @@ impl<'tcx> crate::MirPass<'tcx> for AddCallGuards {
fn run_pass(&self, _tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
let mut pred_count: IndexVec<_, _> =
body.basic_blocks.predecessors().iter().map(|ps| ps.len()).collect();
- pred_count[START_BLOCK] += 1;
// We need a place to store the new blocks generated
let mut new_blocks = Vec::new();
From 5bae3adde9410c4f0f7363ec44b183a255463a0e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tomasz=20Mi=C4=85sko?= <tomasz.miasko@gmail.com>
Date: Wed, 5 Mar 2025 23:41:44 +0100
Subject: [PATCH 2/2] Calculate predecessor count directly
Avoid allocating a vector of small vectors merely to determine how many
predecessors each basic block has.
Additionally use u8 and saturating operations. The pass only needs to
distinguish between [0..1] and [2..].
---
compiler/rustc_mir_transform/src/add_call_guards.rs | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/compiler/rustc_mir_transform/src/add_call_guards.rs b/compiler/rustc_mir_transform/src/add_call_guards.rs
index f9e757dda431c..60e6342d4ecf7 100644
--- a/compiler/rustc_mir_transform/src/add_call_guards.rs
+++ b/compiler/rustc_mir_transform/src/add_call_guards.rs
@@ -32,8 +32,12 @@ pub(super) use self::AddCallGuards::*;
impl<'tcx> crate::MirPass<'tcx> for AddCallGuards {
fn run_pass(&self, _tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
- let mut pred_count: IndexVec<_, _> =
- body.basic_blocks.predecessors().iter().map(|ps| ps.len()).collect();
+ let mut pred_count = IndexVec::from_elem(0u8, &body.basic_blocks);
+ for (_, data) in body.basic_blocks.iter_enumerated() {
+ for succ in data.terminator().successors() {
+ pred_count[succ] = pred_count[succ].saturating_add(1);
+ }
+ }
// We need a place to store the new blocks generated
let mut new_blocks = Vec::new();