Rollup merge of #124293 - oli-obk:miri_intrinsic_fallback_body, r=RalfJung

Let miri and const eval execute intrinsics' fallback bodies

fixes https://github.com/rust-lang/miri/issues/3397

r? ``@RalfJung``

2 files changed, 28 insertions, 0 deletions

diff --git a/src/tools/miri/tests/fail/intrinsic_fallback_checks_ub.rs b/src/tools/miri/tests/fail/intrinsic_fallback_checks_ub.rs
new file mode 100644
index 00000000000..93c9d3d7814
--- /dev/null
+++ b/src/tools/miri/tests/fail/intrinsic_fallback_checks_ub.rs
@@ -0,0 +1,14 @@
+#![feature(rustc_attrs, effects)]
+
+#[rustc_intrinsic]
+#[rustc_nounwind]
+#[rustc_do_not_const_check]
+#[inline]
+pub const fn ptr_guaranteed_cmp<T>(ptr: *const T, other: *const T) -> u8 {
+    (ptr == other) as u8
+}
+
+fn main() {
+    ptr_guaranteed_cmp::<()>(std::ptr::null(), std::ptr::null());
+    //~^ ERROR: can only use intrinsic fallback bodies that check UB.
+}
diff --git a/src/tools/miri/tests/fail/intrinsic_fallback_checks_ub.stderr b/src/tools/miri/tests/fail/intrinsic_fallback_checks_ub.stderr
new file mode 100644
index 00000000000..b37e05c62f9
--- /dev/null
+++ b/src/tools/miri/tests/fail/intrinsic_fallback_checks_ub.stderr
@@ -0,0 +1,14 @@
+error: unsupported operation: miri can only use intrinsic fallback bodies that check UB. After verifying that `ptr_guaranteed_cmp` does so, add the `#[miri::intrinsic_fallback_checks_ub]` attribute to it; also ping @rust-lang/miri when you do that
+  --> $DIR/intrinsic_fallback_checks_ub.rs:LL:CC
+   |
+LL |     ptr_guaranteed_cmp::<()>(std::ptr::null(), std::ptr::null());
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ miri can only use intrinsic fallback bodies that check UB. After verifying that `ptr_guaranteed_cmp` does so, add the `#[miri::intrinsic_fallback_checks_ub]` attribute to it; also ping @rust-lang/miri when you do that
+   |
+   = help: this is likely not a bug in the program; it indicates that the program performed an operation that the interpreter does not support
+   = note: BACKTRACE:
+   = note: inside `main` at $DIR/intrinsic_fallback_checks_ub.rs:LL:CC
+
+note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace
+
+error: aborting due to 1 previous error
+