Rollup merge of #123411 - saethlin:ub-checks, r=Urgau,RalfJung

Put checks that detect UB under their own flag below debug_assertions

Implementation of https://github.com/rust-lang/compiler-team/issues/725

1 files changed, 28 insertions, 0 deletions

diff --git a/tests/codegen/ub-checks.rs b/tests/codegen/ub-checks.rs
new file mode 100644
index 00000000000..de48d74e652
--- /dev/null
+++ b/tests/codegen/ub-checks.rs
@@ -0,0 +1,28 @@
+// With -Zub-checks=yes (enabled by default by -Cdebug-assertions=yes) we will produce a runtime
+// check that the index to slice::get_unchecked is in-bounds of the slice. That is tested for by
+// tests/ui/precondition-checks/out-of-bounds-get-unchecked.rs
+//
+// This test ensures that such a runtime check is *not* emitted when debug-assertions are enabled,
+// but ub-checks are explicitly disabled.
+
+//@ revisions: DEBUG NOCHECKS
+//@ [DEBUG] compile-flags:
+//@ [NOCHECKS] compile-flags: -Zub-checks=no
+//@ compile-flags: -O -Cdebug-assertions=yes
+
+#![crate_type = "lib"]
+
+use std::ops::Range;
+
+// CHECK-LABEL: @slice_get_unchecked(
+#[no_mangle]
+pub unsafe fn slice_get_unchecked(x: &[i32], i: usize) -> &i32 {
+    //    CHECK: icmp ult
+    // NOCHECKS: tail call void @llvm.assume
+    //    DEBUG: br i1
+    //    DEBUG: call core::panicking::panic_nounwind
+    //    DEBUG: unreachable
+    //    CHECK: getelementptr inbounds
+    //    CHECK: ret ptr
+    x.get_unchecked(i)
+}