From 0bcac8a7f25b994ddd3c2deda74dae04c677b816 Mon Sep 17 00:00:00 2001
From: Arthur Carcano <arthur.carcano@ocamlpro.com>
Date: Wed, 2 Aug 2023 14:47:38 +0200
Subject: [PATCH] Add invariant to Vec::pop that len < cap if pop successful
Fixes: https://github.com/rust-lang/rust/issues/114334
---
library/alloc/src/vec/mod.rs | 1 +
tests/codegen/vec_pop_push_noop.rs | 24 ++++++++++++++++++++++++
2 files changed, 25 insertions(+)
create mode 100644 tests/codegen/vec_pop_push_noop.rs
diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs
index 35015238e6e2f..3b12c1bee0b76 100644
--- a/library/alloc/src/vec/mod.rs
+++ b/library/alloc/src/vec/mod.rs
@@ -1956,6 +1956,7 @@ impl<T, A: Allocator> Vec<T, A> {
} else {
unsafe {
self.len -= 1;
+ core::intrinsics::assume(self.len < self.capacity());
Some(ptr::read(self.as_ptr().add(self.len())))
}
}
diff --git a/tests/codegen/vec_pop_push_noop.rs b/tests/codegen/vec_pop_push_noop.rs
new file mode 100644
index 0000000000000..8bc7b68a816ec
--- /dev/null
+++ b/tests/codegen/vec_pop_push_noop.rs
@@ -0,0 +1,24 @@
+// compile-flags: -O
+
+#![crate_type = "lib"]
+
+#[no_mangle]
+// CHECK-LABEL: @noop(
+pub fn noop(v: &mut Vec<u8>) {
+ // CHECK-NOT: reserve_for_push
+ // CHECK-NOT: call
+ // CHECK: tail call void @llvm.assume
+ // CHECK-NOT: reserve_for_push
+ // CHECK-NOT: call
+ // CHECK: ret
+ if let Some(x) = v.pop() {
+ v.push(x)
+ }
+}
+
+#[no_mangle]
+// CHECK-LABEL: @push_byte(
+pub fn push_byte(v: &mut Vec<u8>) {
+ // CHECK: call {{.*}}reserve_for_push
+ v.push(3);
+}