review comment and one more test

compiler/rustc_mir/src/const_eval/machine.rs

@@ -38,6 +38,10 @@ impl<'mir, 'tcx> InterpCx<'mir, 'tcx, CompileTimeInterpreter<'mir, 'tcx>> {
         if instance.def.requires_caller_location(self.tcx()) {
             return Ok(false);
         }
+        // only memoize instrinsics
+        if !matches!(instance.def, InstanceDef::Intrinsic(_)) {
+            return Ok(false);
+        }
         // For the moment we only do this for functions which take no arguments
         // (or all arguments are ZSTs) so that we don't memoize too much.
         if args.iter().any(|a| !a.layout.is_zst()) {
@@ -232,13 +236,8 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
             if ecx.tcx.is_const_fn_raw(def.did) {
                 // If this function is a `const fn` then under certain circumstances we
                 // can evaluate call via the query system, thus memoizing all future calls.
-                match instance.def {
-                    InstanceDef::Intrinsic(_) => {
-                        if ecx.try_eval_const_fn_call(instance, ret, args)? {
-                            return Ok(None);
-                        }
-                    }
-                    _ => {}
+                if ecx.try_eval_const_fn_call(instance, ret, args)? {
+                    return Ok(None);
                 }
             } else {
                 // Some functions we support even if they are non-const -- but avoid testing

src/test/ui/consts/const-eval/heap/alloc_intrinsic_nontransient.rs

@@ -1,11 +1,11 @@
+// run-pass
 #![feature(core_intrinsics)]
 #![feature(const_heap)]
 #![feature(const_raw_ptr_deref)]
 #![feature(const_mut_refs)]
 use std::intrinsics;
 
-const FOO: *const i32 = foo();
-//~^ error: untyped pointers are not allowed in constant
+const FOO: &i32 = foo();
 
 const fn foo() -> &'static i32 {
     let t = unsafe {
@@ -16,5 +16,5 @@ const fn foo() -> &'static i32 {
     unsafe { &*t }
 }
 fn main() {
-    assert_eq!(unsafe { *FOO }, 20)
+    assert_eq!(*FOO, 20)
 }

src/test/ui/consts/const-eval/heap/alloc_intrinsic_nontransient.stderr

@@ -1,8 +0,0 @@
-error: untyped pointers are not allowed in constant
-  --> $DIR/alloc_intrinsic_nontransient.rs:7:1
-   |
-LL | const FOO: *const i32 = foo();
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-error: aborting due to previous error
-

src/test/ui/consts/const-eval/heap/alloc_intrinsic_nontransient_fail.rs

@@ -0,0 +1,20 @@
+// run-pass
+#![feature(core_intrinsics)]
+#![feature(const_heap)]
+#![feature(const_raw_ptr_deref)]
+#![feature(const_mut_refs)]
+use std::intrinsics;
+
+const FOO: &i32 = foo();
+
+const fn foo() -> &'static i32 {
+    let t = unsafe {
+        let i = intrinsics::const_allocate(4, 4) as * mut i32;
+        *i = 20;
+        i
+    };
+    unsafe { &*t }
+}
+fn main() {
+    assert_eq!(*FOO, 20)
+}