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MatchBranchSimplification: Consider empty-unreachable otherwise branch

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This commit is contained in:
clubby789 2024-10-04 20:26:41 +00:00
parent 11f7e302e1
commit e32ec45c02
7 changed files with 81 additions and 48 deletions
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7
compiler/rustc_data_structures/src/packed.rs
View file

@ -18,6 +18,13 @@ impl Pu128 {
}
}
impl From<Pu128> for u128 {
#[inline]
fn from(value: Pu128) -> Self {
value.get()
}
}
impl From<u128> for Pu128 {
#[inline]
fn from(value: u128) -> Self {

11
compiler/rustc_middle/src/mir/terminator.rs
View file

@ -67,6 +67,17 @@ impl SwitchTargets {
&mut self.targets
}
/// Returns a slice with all considered values (not including the fallback).
#[inline]
pub fn all_values(&self) -> &[Pu128] {
&self.values
}
#[inline]
pub fn all_values_mut(&mut self) -> &mut [Pu128] {
&mut self.values
}
/// Finds the `BasicBlock` to which this `SwitchInt` will branch given the
/// specific value. This cannot fail, as it'll return the `otherwise`
/// branch if there's not a specific match for the value.

30
compiler/rustc_mir_transform/src/match_branches.rs
View file

@ -7,6 +7,7 @@ use rustc_middle::mir::*;
use rustc_middle::ty::layout::{IntegerExt, TyAndLayout};
use rustc_middle::ty::{self, ScalarInt, Ty, TyCtxt};
use rustc_type_ir::TyKind::*;
use tracing::instrument;
use super::simplify::simplify_cfg;
@ -51,7 +52,7 @@ impl<'tcx> crate::MirPass<'tcx> for MatchBranchSimplification {
}
trait SimplifyMatch<'tcx> {
/// Simplifies a match statement, returning true if the simplification succeeds, false
/// Simplifies a match statement, returning `Some` if the simplification succeeds, `None`
/// otherwise. Generic code is written here, and we generally don't need a custom
/// implementation.
fn simplify(
@ -159,6 +160,7 @@ struct SimplifyToIf;
/// }
/// ```
impl<'tcx> SimplifyMatch<'tcx> for SimplifyToIf {
#[instrument(level = "debug", skip(self, tcx), ret)]
fn can_simplify(
&mut self,
tcx: TyCtxt<'tcx>,
@ -167,12 +169,15 @@ impl<'tcx> SimplifyMatch<'tcx> for SimplifyToIf {
bbs: &IndexSlice<BasicBlock, BasicBlockData<'tcx>>,
_discr_ty: Ty<'tcx>,
) -> Option<()> {
if targets.iter().len() != 1 {
return None;
}
let (first, second) = match targets.all_targets() {
&[first, otherwise] => (first, otherwise),
&[first, second, otherwise] if bbs[otherwise].is_empty_unreachable() => (first, second),
_ => {
return None;
}
};
// We require that the possible target blocks all be distinct.
let (_, first) = targets.iter().next().unwrap();
let second = targets.otherwise();
if first == second {
return None;
}
@ -221,8 +226,14 @@ impl<'tcx> SimplifyMatch<'tcx> for SimplifyToIf {
discr_local: Local,
discr_ty: Ty<'tcx>,
) {
let (val, first) = targets.iter().next().unwrap();
let second = targets.otherwise();
let ((val, first), second) = match (targets.all_targets(), targets.all_values()) {
(&[first, otherwise], &[val]) => ((val, first), otherwise),
(&[first, second, otherwise], &[val, _]) if bbs[otherwise].is_empty_unreachable() => {
((val, first), second)
}
_ => unreachable!(),
};
// We already checked that first and second are different blocks,
// and bb_idx has a different terminator from both of them.
let first = &bbs[first];
@ -297,7 +308,7 @@ struct SimplifyToExp {
transform_kinds: Vec<TransformKind>,
}
#[derive(Clone, Copy)]
#[derive(Clone, Copy, Debug)]
enum ExpectedTransformKind<'a, 'tcx> {
/// Identical statements.
Same(&'a StatementKind<'tcx>),
@ -362,6 +373,7 @@ impl From<ExpectedTransformKind<'_, '_>> for TransformKind {
/// }
/// ```
impl<'tcx> SimplifyMatch<'tcx> for SimplifyToExp {
#[instrument(level = "debug", skip(self, tcx), ret)]
fn can_simplify(
&mut self,
tcx: TyCtxt<'tcx>,

19
tests/mir-opt/issues/issue_59352.num_to_digit.PreCodegen.after.panic-abort.mir
View file

@ -25,12 +25,12 @@ fn num_to_digit(_1: char) -> u32 {
bb1: {
StorageLive(_3);
_3 = discriminant(_2);
switchInt(move _3) -> [1: bb2, 0: bb6, otherwise: bb8];
StorageDead(_2);
switchInt(move _3) -> [1: bb2, otherwise: bb7];
}
bb2: {
StorageDead(_3);
StorageDead(_2);
StorageLive(_4);
_4 = char::methods::<impl char>::to_digit(move _1, const 8_u32) -> [return: bb3, unwind unreachable];
}
@ -38,7 +38,7 @@ fn num_to_digit(_1: char) -> u32 {
bb3: {
StorageLive(_5);
_5 = discriminant(_4);
switchInt(move _5) -> [0: bb4, 1: bb5, otherwise: bb8];
switchInt(move _5) -> [0: bb4, 1: bb5, otherwise: bb6];
}
bb4: {
@ -49,21 +49,20 @@ fn num_to_digit(_1: char) -> u32 {
_0 = move ((_4 as Some).0: u32);
StorageDead(_5);
StorageDead(_4);
goto -> bb7;
goto -> bb8;
}
bb6: {
StorageDead(_3);
StorageDead(_2);
_0 = const 0_u32;
goto -> bb7;
unreachable;
}
bb7: {
return;
StorageDead(_3);
_0 = const 0_u32;
goto -> bb8;
}
bb8: {
unreachable;
return;
}
}

19
tests/mir-opt/issues/issue_59352.num_to_digit.PreCodegen.after.panic-unwind.mir
View file

@ -25,12 +25,12 @@ fn num_to_digit(_1: char) -> u32 {
bb1: {
StorageLive(_3);
_3 = discriminant(_2);
switchInt(move _3) -> [1: bb2, 0: bb6, otherwise: bb8];
StorageDead(_2);
switchInt(move _3) -> [1: bb2, otherwise: bb7];
}
bb2: {
StorageDead(_3);
StorageDead(_2);
StorageLive(_4);
_4 = char::methods::<impl char>::to_digit(move _1, const 8_u32) -> [return: bb3, unwind continue];
}
@ -38,7 +38,7 @@ fn num_to_digit(_1: char) -> u32 {
bb3: {
StorageLive(_5);
_5 = discriminant(_4);
switchInt(move _5) -> [0: bb4, 1: bb5, otherwise: bb8];
switchInt(move _5) -> [0: bb4, 1: bb5, otherwise: bb6];
}
bb4: {
@ -49,21 +49,20 @@ fn num_to_digit(_1: char) -> u32 {
_0 = move ((_4 as Some).0: u32);
StorageDead(_5);
StorageDead(_4);
goto -> bb7;
goto -> bb8;
}
bb6: {
StorageDead(_3);
StorageDead(_2);
_0 = const 0_u32;
goto -> bb7;
unreachable;
}
bb7: {
return;
StorageDead(_3);
_0 = const 0_u32;
goto -> bb8;
}
bb8: {
unreachable;
return;
}
}

41
tests/mir-opt/matches_reduce_branches.my_is_some.MatchBranchSimplification.diff
View file

@ -5,27 +5,32 @@
debug bar => _1;
let mut _0: bool;
let mut _2: isize;
+ let mut _3: isize;
bb0: {
_2 = discriminant(_1);
switchInt(move _2) -> [0: bb2, 1: bb3, otherwise: bb1];
}
bb1: {
unreachable;
}
bb2: {
_0 = const false;
goto -> bb4;
}
bb3: {
_0 = const true;
goto -> bb4;
}
bb4: {
- switchInt(move _2) -> [0: bb2, 1: bb3, otherwise: bb1];
- }
-
- bb1: {
- unreachable;
- }
-
- bb2: {
- _0 = const false;
- goto -> bb4;
- }
-
- bb3: {
- _0 = const true;
- goto -> bb4;
- }
-
- bb4: {
+ StorageLive(_3);
+ _3 = move _2;
+ _0 = Ne(copy _3, const 0_isize);
+ StorageDead(_3);
return;
}
}

2
tests/mir-opt/matches_reduce_branches.rs
View file

@ -23,7 +23,7 @@ fn foo(bar: Option<()>) {
// Test for #131219.
fn my_is_some(bar: Option<()>) -> bool {
// CHECK-LABEL: fn my_is_some(
// CHECK: switchInt
// CHECK: = Ne
// CHECK: return
match bar {
Some(_) => true,