Auto merge of #89247 - fee1-dead:const-eval-select, r=oli-obk

Add `const_eval_select` intrinsic

Adds an intrinsic that calls a given function when evaluated at compiler time, but generates a call to another function when called at runtime.

See https://github.com/rust-lang/const-eval/issues/7 for previous discussion.

r? `@oli-obk.`

1 files changed, 17 insertions, 0 deletions

diff --git a/src/test/codegen/intrinsics/const_eval_select.rs b/src/test/codegen/intrinsics/const_eval_select.rs
new file mode 100644
index 00000000000..34e653b4b9d
--- /dev/null
+++ b/src/test/codegen/intrinsics/const_eval_select.rs
@@ -0,0 +1,17 @@
+// compile-flags: -C no-prepopulate-passes
+
+#![crate_type = "lib"]
+#![feature(const_eval_select)]
+
+use std::intrinsics::const_eval_select;
+
+const fn foo(_: i32) -> i32 { 1 }
+
+#[no_mangle]
+pub fn hi(n: i32) -> i32 { n }
+
+#[no_mangle]
+pub unsafe fn hey() {
+    // CHECK: call i32 @hi(i32
+    const_eval_select((42,), foo, hi);
+}