Do not optimize MIR for comptime ConstFns

compiler/rustc_middle/src/mir/pretty.rs

@@ -5,6 +5,7 @@ use std::{fs, io};
 
 use rustc_abi::Size;
 use rustc_ast::InlineAsmTemplatePiece;
+use rustc_hir::Constness;
 use tracing::trace;
 use ty::print::PrettyPrinter;
 
@@ -340,12 +341,18 @@ pub fn write_mir_pretty<'tcx>(tcx: TyCtxt<'tcx>, w: &mut dyn io::Write) -> io::R
 
         // For `const fn` we want to render both the optimized MIR and the MIR for ctfe.
         if tcx.is_const_fn(def_id) {
-            render_body(w, tcx.optimized_mir(def_id))?;
-            writeln!(w)?;
-            writeln!(w, "// MIR FOR CTFE")?;
-            // Do not use `render_body`, as that would render the promoteds again, but these
-            // are shared between mir_for_ctfe and optimized_mir
-            writer.write_mir_fn(tcx.mir_for_ctfe(def_id), w)?;
+            // In case where comptime const fn, should only render the MIR for ctfe,
+            // since comptime functions cannot have their MIR optimized
+            if matches!(tcx.constness(def_id), Constness::Const { always: true }) {
+                render_body(w, tcx.mir_for_ctfe(def_id))?;
+            } else {
+                render_body(w, tcx.optimized_mir(def_id))?;
+                writeln!(w)?;
+                writeln!(w, "// MIR FOR CTFE")?;
+                // Do not use `render_body`, as that would render the promoteds again, but these
+                // are shared between mir_for_ctfe and optimized_mir
+                writer.write_mir_fn(tcx.mir_for_ctfe(def_id), w)?;
+            }
         } else {
             if let Some((val, ty)) = tcx.trivial_const(def_id) {
                 ty::print::with_forced_impl_filename_line! {

src/tools/clippy/clippy_lints/src/redundant_clone.rs

@@ -7,7 +7,7 @@ use clippy_utils::{fn_has_unsatisfiable_clauses, sym};
 use rustc_errors::Applicability;
 use rustc_hir::attrs::lang_items::LangItem;
 use rustc_hir::intravisit::FnKind;
-use rustc_hir::{Body, FnDecl, def_id};
+use rustc_hir::{Body, Constness, FnDecl, def_id};
 use rustc_lint::{LateContext, LateLintPass, declare_lint_pass};
 use rustc_middle::mir;
 use rustc_middle::ty::{self, Ty};
@@ -69,7 +69,13 @@ impl<'tcx> LateLintPass<'tcx> for RedundantClone {
             return;
         }
 
-        let mir = cx.tcx.optimized_mir(def_id.to_def_id());
+        // Optimizing MIR for `#[rustc_comptime]` functions causes ICE,
+        // so giving MIR for CTFE for comptime functions instead
+        let mir = if matches!(cx.tcx.constness(def_id.to_def_id()), Constness::Const { always: true }) {
+            cx.tcx.mir_for_ctfe(def_id.to_def_id())
+        } else {
+            cx.tcx.optimized_mir(def_id.to_def_id())
+        };
 
         let mut possible_borrower = PossibleBorrowerMap::new(cx, mir);
 

src/tools/clippy/tests/ui/redundant_clone-comptime.fixed

@@ -0,0 +1,20 @@
+// rustfix-only-machine-applicable
+#![feature(rustc_attrs, const_trait_impl, const_clone, const_destruct)]
+#![warn(clippy::redundant_clone)]
+
+struct S;
+
+const impl Clone for S {
+    fn clone(&self) -> Self {
+        Self
+    }
+}
+
+#[rustc_comptime]
+fn comptime_func() {
+    let a = S;
+    let _a = a;
+    //~^ redundant_clone
+}
+
+fn main() {}

src/tools/clippy/tests/ui/redundant_clone-comptime.rs

@@ -0,0 +1,20 @@
+// rustfix-only-machine-applicable
+#![feature(rustc_attrs, const_trait_impl, const_clone, const_destruct)]
+#![warn(clippy::redundant_clone)]
+
+struct S;
+
+const impl Clone for S {
+    fn clone(&self) -> Self {
+        Self
+    }
+}
+
+#[rustc_comptime]
+fn comptime_func() {
+    let a = S;
+    let _a = a.clone();
+    //~^ redundant_clone
+}
+
+fn main() {}

src/tools/clippy/tests/ui/redundant_clone-comptime.stderr

@@ -0,0 +1,16 @@
+error: redundant clone
+  --> tests/ui/redundant_clone-comptime.rs:16:15
+   |
+LL |     let _a = a.clone();
+   |               ^^^^^^^^ help: remove this
+   |
+note: this value is dropped without further use
+  --> tests/ui/redundant_clone-comptime.rs:16:14
+   |
+LL |     let _a = a.clone();
+   |              ^
+   = note: `-D clippy::redundant-clone` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::redundant_clone)]`
+
+error: aborting due to 1 previous error
+

tests/ui/comptime/emit-mir.rs

@@ -0,0 +1,8 @@
+//@ check-pass
+//@ compile-flags: --emit=mir
+#![feature(rustc_attrs)]
+
+#[rustc_comptime]
+fn comptime_fn() {}
+
+fn main() {}