From 15c01eb22c8f7abbfe6d49dc5824c239547a0323 Mon Sep 17 00:00:00 2001
From: Oli Scherer <github333195615777966@oli-obk.de>
Date: Wed, 18 Dec 2024 18:37:54 +0000
Subject: [PATCH] Fix cycle error only occurring with -Zdump-mir

---
 compiler/rustc_middle/src/mir/pretty.rs       | 24 ++++++++++++-------
 tests/mir-opt/building/dump_mir_cycle.rs      | 19 +++++++++++++++
 ...0].SimplifyCfg-pre-optimizations.after.mir |  4 +---
 ...motion_extern_static.BAR.PromoteTemps.diff |  6 ++---
 4 files changed, 37 insertions(+), 16 deletions(-)
 create mode 100644 tests/mir-opt/building/dump_mir_cycle.rs

diff --git a/compiler/rustc_middle/src/mir/pretty.rs b/compiler/rustc_middle/src/mir/pretty.rs
index 47522f00bb1b3..24d2478f77018 100644
--- a/compiler/rustc_middle/src/mir/pretty.rs
+++ b/compiler/rustc_middle/src/mir/pretty.rs
@@ -1555,16 +1555,22 @@ pub fn write_allocations<'tcx>(
                 write!(w, " (vtable: impl {dyn_ty} for {ty})")?
             }
             Some(GlobalAlloc::Static(did)) if !tcx.is_foreign_item(did) => {
-                match tcx.eval_static_initializer(did) {
-                    Ok(alloc) => {
-                        write!(w, " (static: {}, ", tcx.def_path_str(did))?;
-                        write_allocation_track_relocs(w, alloc)?;
+                write!(w, " (static: {}", tcx.def_path_str(did))?;
+                if body.phase <= MirPhase::Runtime(RuntimePhase::PostCleanup)
+                    && tcx.hir().body_const_context(body.source.def_id()).is_some()
+                {
+                    // Statics may be cyclic and evaluating them too early
+                    // in the MIR pipeline may cause cycle errors even though
+                    // normal compilation is fine.
+                    write!(w, ")")?;
+                } else {
+                    match tcx.eval_static_initializer(did) {
+                        Ok(alloc) => {
+                            write!(w, ", ")?;
+                            write_allocation_track_relocs(w, alloc)?;
+                        }
+                        Err(_) => write!(w, ", error during initializer evaluation)")?,
                     }
-                    Err(_) => write!(
-                        w,
-                        " (static: {}, error during initializer evaluation)",
-                        tcx.def_path_str(did)
-                    )?,
                 }
             }
             Some(GlobalAlloc::Static(did)) => {
diff --git a/tests/mir-opt/building/dump_mir_cycle.rs b/tests/mir-opt/building/dump_mir_cycle.rs
new file mode 100644
index 0000000000000..8e13420aed790
--- /dev/null
+++ b/tests/mir-opt/building/dump_mir_cycle.rs
@@ -0,0 +1,19 @@
+#[derive(Debug)]
+pub struct Thing {
+    pub next: &'static Thing,
+}
+
+pub static THING: Thing = Thing { next: &THING };
+// CHECK: alloc{{.+}} (static: THING)
+
+const fn thing() -> &'static Thing {
+    &MUTUALLY_RECURSIVE
+}
+
+pub static MUTUALLY_RECURSIVE: Thing = Thing { next: thing() };
+// CHECK: alloc{{.+}} (static: MUTUALLY_RECURSIVE)
+
+fn main() {
+    // Generate optimized MIR for the const fn, too.
+    thing();
+}
diff --git a/tests/mir-opt/const_promotion_extern_static.BAR-promoted[0].SimplifyCfg-pre-optimizations.after.mir b/tests/mir-opt/const_promotion_extern_static.BAR-promoted[0].SimplifyCfg-pre-optimizations.after.mir
index 7affbf6dd403f..344851bb08839 100644
--- a/tests/mir-opt/const_promotion_extern_static.BAR-promoted[0].SimplifyCfg-pre-optimizations.after.mir
+++ b/tests/mir-opt/const_promotion_extern_static.BAR-promoted[0].SimplifyCfg-pre-optimizations.after.mir
@@ -15,6 +15,4 @@ const BAR::promoted[0]: &[&i32; 1] = {
     }
 }
 
-ALLOC0 (static: Y, size: 4, align: 4) {
-    2a 00 00 00                                     │ *...
-}
+ALLOC0 (static: Y)
diff --git a/tests/mir-opt/const_promotion_extern_static.BAR.PromoteTemps.diff b/tests/mir-opt/const_promotion_extern_static.BAR.PromoteTemps.diff
index 487f68a8d4dfe..5f8f84244af6c 100644
--- a/tests/mir-opt/const_promotion_extern_static.BAR.PromoteTemps.diff
+++ b/tests/mir-opt/const_promotion_extern_static.BAR.PromoteTemps.diff
@@ -38,9 +38,7 @@
       bb2 (cleanup): {
           resume;
       }
-- }
-- 
-- ALLOC0 (static: Y, size: 4, align: 4) {
--     2a 00 00 00                                     │ *...
   }
+- 
+- ALLOC0 (static: Y)