From adf53d4b068e216f0705ba2baae4cc21dd0988a3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tomasz=20Mi=C4=85sko?= <tomasz.miasko@gmail.com>
Date: Fri, 16 Dec 2022 00:00:00 +0000
Subject: [PATCH] Remove dead code after destination propagation
---
compiler/rustc_mir_transform/src/dest_prop.rs | 7 ++
.../unreachable.f.DestinationPropagation.diff | 86 +++++++++++++++++++
src/test/mir-opt/dest-prop/unreachable.rs | 18 ++++
3 files changed, 111 insertions(+)
create mode 100644 src/test/mir-opt/dest-prop/unreachable.f.DestinationPropagation.diff
create mode 100644 src/test/mir-opt/dest-prop/unreachable.rs
diff --git a/compiler/rustc_mir_transform/src/dest_prop.rs b/compiler/rustc_mir_transform/src/dest_prop.rs
index 3e45319431cec..74d8337653f03 100644
--- a/compiler/rustc_mir_transform/src/dest_prop.rs
+++ b/compiler/rustc_mir_transform/src/dest_prop.rs
@@ -129,6 +129,7 @@
use std::collections::hash_map::{Entry, OccupiedEntry};
+use crate::simplify::remove_dead_blocks;
use crate::MirPass;
use rustc_data_structures::fx::FxHashMap;
use rustc_index::bit_set::BitSet;
@@ -235,6 +236,12 @@ impl<'tcx> MirPass<'tcx> for DestinationPropagation {
apply_merges(body, tcx, &merges, &merged_locals);
}
+ if round_count != 0 {
+ // Merging can introduce overlap between moved arguments and/or call destination in an
+ // unreachable code, which validator considers to be ill-formed.
+ remove_dead_blocks(tcx, body);
+ }
+
trace!(round_count);
}
}
diff --git a/src/test/mir-opt/dest-prop/unreachable.f.DestinationPropagation.diff b/src/test/mir-opt/dest-prop/unreachable.f.DestinationPropagation.diff
new file mode 100644
index 0000000000000..9ea756c271298
--- /dev/null
+++ b/src/test/mir-opt/dest-prop/unreachable.f.DestinationPropagation.diff
@@ -0,0 +1,86 @@
+- // MIR for `f` before DestinationPropagation
++ // MIR for `f` after DestinationPropagation
+
+ fn f(_1: T) -> () {
+ debug a => _1; // in scope 0 at $DIR/unreachable.rs:+0:19: +0:20
+ let mut _0: (); // return place in scope 0 at $DIR/unreachable.rs:+0:25: +0:25
+ let _2: T; // in scope 0 at $DIR/unreachable.rs:+1:9: +1:10
+ let mut _3: bool; // in scope 0 at $DIR/unreachable.rs:+2:8: +2:13
+ let _4: (); // in scope 0 at $DIR/unreachable.rs:+3:9: +3:16
+ let mut _5: T; // in scope 0 at $DIR/unreachable.rs:+3:11: +3:12
+ let mut _6: T; // in scope 0 at $DIR/unreachable.rs:+3:14: +3:15
+ let _7: (); // in scope 0 at $DIR/unreachable.rs:+5:9: +5:16
+ let mut _8: T; // in scope 0 at $DIR/unreachable.rs:+5:11: +5:12
+ let mut _9: T; // in scope 0 at $DIR/unreachable.rs:+5:14: +5:15
+ scope 1 {
+- debug b => _2; // in scope 1 at $DIR/unreachable.rs:+1:9: +1:10
++ debug b => _1; // in scope 1 at $DIR/unreachable.rs:+1:9: +1:10
+ }
+
+ bb0: {
+- StorageLive(_2); // scope 0 at $DIR/unreachable.rs:+1:9: +1:10
+- _2 = _1; // scope 0 at $DIR/unreachable.rs:+1:13: +1:14
++ nop; // scope 0 at $DIR/unreachable.rs:+1:9: +1:10
++ nop; // scope 0 at $DIR/unreachable.rs:+1:13: +1:14
+ StorageLive(_3); // scope 1 at $DIR/unreachable.rs:+2:8: +2:13
+ _3 = const false; // scope 1 at $DIR/unreachable.rs:+2:8: +2:13
+- goto -> bb3; // scope 1 at $DIR/unreachable.rs:+2:8: +2:13
++ goto -> bb1; // scope 1 at $DIR/unreachable.rs:+2:8: +2:13
+ }
+
+ bb1: {
+- StorageLive(_4); // scope 1 at $DIR/unreachable.rs:+3:9: +3:16
+- StorageLive(_5); // scope 1 at $DIR/unreachable.rs:+3:11: +3:12
+- _5 = _1; // scope 1 at $DIR/unreachable.rs:+3:11: +3:12
+- StorageLive(_6); // scope 1 at $DIR/unreachable.rs:+3:14: +3:15
+- _6 = _2; // scope 1 at $DIR/unreachable.rs:+3:14: +3:15
+- _4 = g::<T>(move _5, move _6) -> bb2; // scope 1 at $DIR/unreachable.rs:+3:9: +3:16
+- // mir::Constant
+- // + span: $DIR/unreachable.rs:11:9: 11:10
+- // + literal: Const { ty: fn(T, T) {g::<T>}, val: Value(<ZST>) }
+- }
+-
+- bb2: {
+- StorageDead(_6); // scope 1 at $DIR/unreachable.rs:+3:15: +3:16
+- StorageDead(_5); // scope 1 at $DIR/unreachable.rs:+3:15: +3:16
+- StorageDead(_4); // scope 1 at $DIR/unreachable.rs:+3:16: +3:17
+- _0 = const (); // scope 1 at $DIR/unreachable.rs:+2:14: +4:6
+- goto -> bb5; // scope 1 at $DIR/unreachable.rs:+2:5: +6:6
+- }
+-
+- bb3: {
+ StorageLive(_7); // scope 1 at $DIR/unreachable.rs:+5:9: +5:16
+- StorageLive(_8); // scope 1 at $DIR/unreachable.rs:+5:11: +5:12
+- _8 = _2; // scope 1 at $DIR/unreachable.rs:+5:11: +5:12
++ nop; // scope 1 at $DIR/unreachable.rs:+5:11: +5:12
++ nop; // scope 1 at $DIR/unreachable.rs:+5:11: +5:12
+ StorageLive(_9); // scope 1 at $DIR/unreachable.rs:+5:14: +5:15
+- _9 = _2; // scope 1 at $DIR/unreachable.rs:+5:14: +5:15
+- _7 = g::<T>(move _8, move _9) -> bb4; // scope 1 at $DIR/unreachable.rs:+5:9: +5:16
++ _9 = _1; // scope 1 at $DIR/unreachable.rs:+5:14: +5:15
++ _7 = g::<T>(move _1, move _9) -> bb2; // scope 1 at $DIR/unreachable.rs:+5:9: +5:16
+ // mir::Constant
+ // + span: $DIR/unreachable.rs:13:9: 13:10
+ // + literal: Const { ty: fn(T, T) {g::<T>}, val: Value(<ZST>) }
+ }
+
+- bb4: {
++ bb2: {
+ StorageDead(_9); // scope 1 at $DIR/unreachable.rs:+5:15: +5:16
+- StorageDead(_8); // scope 1 at $DIR/unreachable.rs:+5:15: +5:16
++ nop; // scope 1 at $DIR/unreachable.rs:+5:15: +5:16
+ StorageDead(_7); // scope 1 at $DIR/unreachable.rs:+5:16: +5:17
+ _0 = const (); // scope 1 at $DIR/unreachable.rs:+4:12: +6:6
+- goto -> bb5; // scope 1 at $DIR/unreachable.rs:+2:5: +6:6
++ goto -> bb3; // scope 1 at $DIR/unreachable.rs:+2:5: +6:6
+ }
+
+- bb5: {
++ bb3: {
+ StorageDead(_3); // scope 1 at $DIR/unreachable.rs:+6:5: +6:6
+- StorageDead(_2); // scope 0 at $DIR/unreachable.rs:+7:1: +7:2
++ nop; // scope 0 at $DIR/unreachable.rs:+7:1: +7:2
+ return; // scope 0 at $DIR/unreachable.rs:+7:2: +7:2
+ }
+ }
+
diff --git a/src/test/mir-opt/dest-prop/unreachable.rs b/src/test/mir-opt/dest-prop/unreachable.rs
new file mode 100644
index 0000000000000..32b5def984a80
--- /dev/null
+++ b/src/test/mir-opt/dest-prop/unreachable.rs
@@ -0,0 +1,18 @@
+// Check that unreachable code is removed after the destination propagation.
+// Regression test for issue #105428.
+//
+// compile-flags: --crate-type=lib -Zmir-opt-level=0
+// compile-flags: -Zmir-enable-passes=+ConstProp,+SimplifyConstCondition-after-const-prop,+DestinationPropagation
+
+// EMIT_MIR unreachable.f.DestinationPropagation.diff
+pub fn f<T: Copy>(a: T) {
+ let b = a;
+ if false {
+ g(a, b);
+ } else {
+ g(b, b);
+ }
+}
+
+#[inline(never)]
+pub fn g<T: Copy>(_: T, _: T) {}