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Asserts the maximum value that can be returned from Vec::len 
1 parent 4790a43 commit b5ea631

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4 files changed

+72
-2
lines changed

4 files changed

+72
-2
lines changed

‎library/alloc/src/vec/mod.rs‎

Lines changed: 9 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -56,7 +56,6 @@
5656
#[cfg(not(no_global_oom_handling))]
5757
use core::cmp;
5858
use core::cmp::Ordering;
59-
use core::fmt;
6059
use core::hash::{Hash, Hasher};
6160
#[cfg(not(no_global_oom_handling))]
6261
use core::iter;
@@ -65,6 +64,7 @@ use core::mem::{self, ManuallyDrop, MaybeUninit, SizedTypeProperties};
6564
use core::ops::{self, Index, IndexMut, Range, RangeBounds};
6665
use core::ptr::{self, NonNull};
6766
use core::slice::{self, SliceIndex};
67+
use core::{fmt, intrinsics};
6868

6969
#[unstable(feature = "extract_if", reason = "recently added", issue = "43244")]
7070
pub use self::extract_if::ExtractIf;
@@ -2675,7 +2675,14 @@ impl<T, A: Allocator> Vec<T, A> {
26752675
#[rustc_const_unstable(feature = "const_vec_string_slice", issue = "129041")]
26762676
#[rustc_confusables("length", "size")]
26772677
pub const fn len(&self) -> usize {
2678-
self.len
2678+
let len = self.len;
2679+
2680+
// SAFETY: The maximum capacity of `Vec<T>` is `isize::MAX` bytes, so the maximum value can
2681+
// be returned is `usize::checked_div(mem::size_of::<T>()).unwrap_or(usize::MAX)`, which
2682+
// matches the definition of `T::MAX_SLICE_LEN`.
2683+
unsafe { intrinsics::assume(len <= T::MAX_SLICE_LEN) };
2684+
2685+
len
26792686
}
26802687

26812688
/// Returns `true` if the vector contains no elements.

‎library/core/src/mem/mod.rs‎

Lines changed: 11 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1241,6 +1241,17 @@ pub trait SizedTypeProperties: Sized {
12411241
#[doc(hidden)]
12421242
#[unstable(feature = "sized_type_properties", issue = "none")]
12431243
const LAYOUT: Layout = Layout::new::<Self>();
1244+
1245+
/// The largest safe length for a `[Self]`.
1246+
///
1247+
/// Anything larger than this would make `size_of_val` overflow `isize::MAX`,
1248+
/// which is never allowed for a single object.
1249+
#[doc(hidden)]
1250+
#[unstable(feature = "sized_type_properties", issue = "none")]
1251+
const MAX_SLICE_LEN: usize = match size_of::<Self>() {
1252+
0 => usize::MAX,
1253+
n => (isize::MAX as usize) / n,
1254+
};
12441255
}
12451256
#[doc(hidden)]
12461257
#[unstable(feature = "sized_type_properties", issue = "none")]

‎tests/codegen/vec-in-place.rs‎

Lines changed: 46 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -36,6 +36,9 @@ pub struct Baz {
3636
// CHECK-LABEL: @vec_iterator_cast_primitive
3737
#[no_mangle]
3838
pub fn vec_iterator_cast_primitive(vec: Vec<i8>) -> Vec<u8> {
39+
// CHECK-NOT: loop
40+
// CHECK: call
41+
// CHECK-SAME: void @llvm.assume(i1 %{{.+}})
3942
// CHECK-NOT: loop
4043
// CHECK-NOT: call
4144
vec.into_iter().map(|e| e as u8).collect()
@@ -44,14 +47,37 @@ pub fn vec_iterator_cast_primitive(vec: Vec<i8>) -> Vec<u8> {
4447
// CHECK-LABEL: @vec_iterator_cast_wrapper
4548
#[no_mangle]
4649
pub fn vec_iterator_cast_wrapper(vec: Vec<u8>) -> Vec<Wrapper<u8>> {
50+
// CHECK-NOT: loop
51+
// CHECK: call
52+
// CHECK-SAME: void @llvm.assume(i1 %{{.+}})
4753
// CHECK-NOT: loop
4854
// CHECK-NOT: call
4955
vec.into_iter().map(|e| Wrapper(e)).collect()
5056
}
5157

58+
// CHECK-LABEL: @vec_iterator_cast_signed
59+
#[no_mangle]
60+
pub fn vec_iterator_cast_signed(vec: Vec<i32>) -> Vec<u32> {
61+
// CHECK-NOT: and i{{[0-9]+}} %{{.*}}, {{[0-9]+}}
62+
vec.into_iter().map(|e| u32::from_ne_bytes(e.to_ne_bytes())).collect()
63+
}
64+
65+
// CHECK-LABEL: @vec_iterator_cast_signed_nested
66+
#[no_mangle]
67+
pub fn vec_iterator_cast_signed_nested(vec: Vec<Vec<i32>>) -> Vec<Vec<u32>> {
68+
// CHECK-NOT: br i1 %{{.*}}, label %{{.*}}, label %{{.*}}
69+
// CHECK-NOT: %{{.*}} = udiv
70+
vec.into_iter()
71+
.map(|e| e.into_iter().map(|e| u32::from_ne_bytes(e.to_ne_bytes())).collect())
72+
.collect()
73+
}
74+
5275
// CHECK-LABEL: @vec_iterator_cast_unwrap
5376
#[no_mangle]
5477
pub fn vec_iterator_cast_unwrap(vec: Vec<Wrapper<u8>>) -> Vec<u8> {
78+
// CHECK-NOT: loop
79+
// CHECK: call
80+
// CHECK-SAME: void @llvm.assume(i1 %{{.+}})
5581
// CHECK-NOT: loop
5682
// CHECK-NOT: call
5783
vec.into_iter().map(|e| e.0).collect()
@@ -60,6 +86,9 @@ pub fn vec_iterator_cast_unwrap(vec: Vec<Wrapper<u8>>) -> Vec<u8> {
6086
// CHECK-LABEL: @vec_iterator_cast_aggregate
6187
#[no_mangle]
6288
pub fn vec_iterator_cast_aggregate(vec: Vec<[u64; 4]>) -> Vec<Foo> {
89+
// CHECK-NOT: loop
90+
// CHECK: call
91+
// CHECK-SAME: void @llvm.assume(i1 %{{.+}})
6392
// CHECK-NOT: loop
6493
// CHECK-NOT: call
6594
vec.into_iter().map(|e| unsafe { std::mem::transmute(e) }).collect()
@@ -68,6 +97,9 @@ pub fn vec_iterator_cast_aggregate(vec: Vec<[u64; 4]>) -> Vec<Foo> {
6897
// CHECK-LABEL: @vec_iterator_cast_deaggregate_tra
6998
#[no_mangle]
7099
pub fn vec_iterator_cast_deaggregate_tra(vec: Vec<Bar>) -> Vec<[u64; 4]> {
100+
// CHECK-NOT: loop
101+
// CHECK: call
102+
// CHECK-SAME: void @llvm.assume(i1 %{{.+}})
71103
// CHECK-NOT: loop
72104
// CHECK-NOT: call
73105

@@ -81,6 +113,9 @@ pub fn vec_iterator_cast_deaggregate_tra(vec: Vec<Bar>) -> Vec<[u64; 4]> {
81113
// CHECK-LABEL: @vec_iterator_cast_deaggregate_fold
82114
#[no_mangle]
83115
pub fn vec_iterator_cast_deaggregate_fold(vec: Vec<Baz>) -> Vec<[u64; 4]> {
116+
// CHECK-NOT: loop
117+
// CHECK: call
118+
// CHECK-SAME: void @llvm.assume(i1 %{{.+}})
84119
// CHECK-NOT: loop
85120
// CHECK-NOT: call
86121

@@ -94,6 +129,11 @@ pub fn vec_iterator_cast_deaggregate_fold(vec: Vec<Baz>) -> Vec<[u64; 4]> {
94129
// CHECK-LABEL: @vec_iterator_cast_unwrap_drop
95130
#[no_mangle]
96131
pub fn vec_iterator_cast_unwrap_drop(vec: Vec<Wrapper<String>>) -> Vec<String> {
132+
// CHECK-NOT: br i1 %{{.*}}, label %{{.*}}, label %{{.*}}
133+
// CHECK-NOT: %{{.*}} = mul
134+
// CHECK-NOT: %{{.*}} = udiv
135+
// CHECK: call
136+
// CHECK-SAME: void @llvm.assume(i1 %{{.+}})
97137
// CHECK-NOT: br i1 %{{.*}}, label %{{.*}}, label %{{.*}}
98138
// CHECK-NOT: call
99139
// CHECK-NOT: %{{.*}} = mul
@@ -105,10 +145,16 @@ pub fn vec_iterator_cast_unwrap_drop(vec: Vec<Wrapper<String>>) -> Vec<String> {
105145
// CHECK-LABEL: @vec_iterator_cast_wrap_drop
106146
#[no_mangle]
107147
pub fn vec_iterator_cast_wrap_drop(vec: Vec<String>) -> Vec<Wrapper<String>> {
148+
// CHECK-NOT: br i1 %{{.*}}, label %{{.*}}, label %{{.*}}
149+
// CHECK-NOT: %{{.*}} = mul
150+
// CHECK-NOT: %{{.*}} = udiv
151+
// CHECK: call
152+
// CHECK-SAME: void @llvm.assume(i1 %{{.+}})
108153
// CHECK-NOT: br i1 %{{.*}}, label %{{.*}}, label %{{.*}}
109154
// CHECK-NOT: call
110155
// CHECK-NOT: %{{.*}} = mul
111156
// CHECK-NOT: %{{.*}} = udiv
157+
// CHECK: ret void
112158

113159
vec.into_iter().map(Wrapper).collect()
114160
}

‎tests/codegen/vec_pop_push_noop.rs‎

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1,3 +1,6 @@
1+
//@ revisions: llvm-pre-19 llvm-19
2+
//@ [llvm-19] min-llvm-version: 19
3+
//@ [llvm-pre-19] max-llvm-major-version: 18
14
//@ compile-flags: -O
25

36
#![crate_type = "lib"]
@@ -9,6 +12,9 @@ pub fn noop(v: &mut Vec<u8>) {
912
// CHECK-NOT: call
1013
// CHECK: tail call void @llvm.assume
1114
// CHECK-NOT: grow_one
15+
// llvm-pre-19: call
16+
// llvm-pre-19-same: void @llvm.assume
17+
// llvm-pre-19-NOT: grow_one
1218
// CHECK-NOT: call
1319
// CHECK: ret
1420
if let Some(x) = v.pop() {

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