From b0b7c860e13858cbc344dcf2baf860752e3a2dd3 Mon Sep 17 00:00:00 2001
From: Ben Kimock <kimockb@gmail.com>
Date: Thu, 4 Apr 2024 00:10:01 -0400
Subject: [PATCH] Teach MIR inliner query cycle avoidance about
 const_eval_select

---
 .../rustc_mir_transform/src/inline/cycle.rs    | 18 ++++++++++++++----
 tests/ui/mir/const_eval_select_cycle.rs        | 18 ++++++++++++++++++
 2 files changed, 32 insertions(+), 4 deletions(-)
 create mode 100644 tests/ui/mir/const_eval_select_cycle.rs

diff --git a/compiler/rustc_mir_transform/src/inline/cycle.rs b/compiler/rustc_mir_transform/src/inline/cycle.rs
index f2b6dcac58632..85e74a69ccedd 100644
--- a/compiler/rustc_mir_transform/src/inline/cycle.rs
+++ b/compiler/rustc_mir_transform/src/inline/cycle.rs
@@ -5,6 +5,7 @@ use rustc_middle::mir::TerminatorKind;
 use rustc_middle::ty::TypeVisitableExt;
 use rustc_middle::ty::{self, GenericArgsRef, InstanceDef, TyCtxt};
 use rustc_session::Limit;
+use rustc_span::sym;
 
 // FIXME: check whether it is cheaper to precompute the entire call graph instead of invoking
 // this query ridiculously often.
@@ -164,11 +165,20 @@ pub(crate) fn mir_inliner_callees<'tcx>(
     let mut calls = FxIndexSet::default();
     for bb_data in body.basic_blocks.iter() {
         let terminator = bb_data.terminator();
-        if let TerminatorKind::Call { func, .. } = &terminator.kind {
+        if let TerminatorKind::Call { func, args: call_args, .. } = &terminator.kind {
             let ty = func.ty(&body.local_decls, tcx);
-            let call = match ty.kind() {
-                ty::FnDef(def_id, args) => (*def_id, *args),
-                _ => continue,
+            let ty::FnDef(def_id, generic_args) = ty.kind() else {
+                continue;
+            };
+            let call = if tcx.is_intrinsic(*def_id, sym::const_eval_select) {
+                let func = &call_args[2].node;
+                let ty = func.ty(&body.local_decls, tcx);
+                let ty::FnDef(def_id, generic_args) = ty.kind() else {
+                    continue;
+                };
+                (*def_id, *generic_args)
+            } else {
+                (*def_id, *generic_args)
             };
             calls.insert(call);
         }
diff --git a/tests/ui/mir/const_eval_select_cycle.rs b/tests/ui/mir/const_eval_select_cycle.rs
new file mode 100644
index 0000000000000..0b84455b2f7fb
--- /dev/null
+++ b/tests/ui/mir/const_eval_select_cycle.rs
@@ -0,0 +1,18 @@
+// Regression test for #122659
+//@ build-pass
+//@ compile-flags: -O --crate-type=lib
+
+#![feature(core_intrinsics)]
+#![feature(const_eval_select)]
+
+use std::intrinsics::const_eval_select;
+
+#[inline]
+pub const fn f() {
+    const_eval_select((), g, g)
+}
+
+#[inline]
+pub const fn g() {
+    const_eval_select((), f, f)
+}