From 484152d562f6babaacb3fae08cc5f70ee550e9ee Mon Sep 17 00:00:00 2001
From: Maybe Waffle <waffle.lapkin@gmail.com>
Date: Thu, 15 Feb 2024 19:54:37 +0000
Subject: Support tail calls in mir via `TerminatorKind::TailCall`

---
 compiler/rustc_const_eval/src/check_consts/check.rs       | 15 ++++++++++++---
 .../src/check_consts/post_drop_elaboration.rs             |  1 +
 compiler/rustc_const_eval/src/interpret/terminator.rs     |  2 ++
 3 files changed, 15 insertions(+), 3 deletions(-)

(limited to 'compiler/rustc_const_eval')

diff --git a/compiler/rustc_const_eval/src/check_consts/check.rs b/compiler/rustc_const_eval/src/check_consts/check.rs
index 0d8a17775dd..412effba32d 100644
--- a/compiler/rustc_const_eval/src/check_consts/check.rs
+++ b/compiler/rustc_const_eval/src/check_consts/check.rs
@@ -135,6 +135,8 @@ impl<'mir, 'tcx> Qualifs<'mir, 'tcx> {
         ccx: &'mir ConstCx<'mir, 'tcx>,
         tainted_by_errors: Option<ErrorGuaranteed>,
     ) -> ConstQualifs {
+        // FIXME(explicit_tail_calls): uhhhh I think we can return without return now, does it change anything
+
         // Find the `Return` terminator if one exists.
         //
         // If no `Return` terminator exists, this MIR is divergent. Just return the conservative
@@ -711,7 +713,14 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
         self.super_terminator(terminator, location);
 
         match &terminator.kind {
-            TerminatorKind::Call { func, args, fn_span, call_source, .. } => {
+            TerminatorKind::Call { func, args, fn_span, .. }
+            | TerminatorKind::TailCall { func, args, fn_span, .. } => {
+                let call_source = match terminator.kind {
+                    TerminatorKind::Call { call_source, .. } => call_source,
+                    TerminatorKind::TailCall { .. } => CallSource::Normal,
+                    _ => unreachable!(),
+                };
+
                 let ConstCx { tcx, body, param_env, .. } = *self.ccx;
                 let caller = self.def_id();
 
@@ -783,7 +792,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                             callee,
                             args: fn_args,
                             span: *fn_span,
-                            call_source: *call_source,
+                            call_source,
                             feature: Some(if tcx.features().const_trait_impl {
                                 sym::effects
                             } else {
@@ -830,7 +839,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                         callee,
                         args: fn_args,
                         span: *fn_span,
-                        call_source: *call_source,
+                        call_source,
                         feature: None,
                     });
                     return;
diff --git a/compiler/rustc_const_eval/src/check_consts/post_drop_elaboration.rs b/compiler/rustc_const_eval/src/check_consts/post_drop_elaboration.rs
index f0763f1e490..f5e745454ab 100644
--- a/compiler/rustc_const_eval/src/check_consts/post_drop_elaboration.rs
+++ b/compiler/rustc_const_eval/src/check_consts/post_drop_elaboration.rs
@@ -108,6 +108,7 @@ impl<'tcx> Visitor<'tcx> for CheckLiveDrops<'_, 'tcx> {
 
             mir::TerminatorKind::UnwindTerminate(_)
             | mir::TerminatorKind::Call { .. }
+            | mir::TerminatorKind::TailCall { .. }
             | mir::TerminatorKind::Assert { .. }
             | mir::TerminatorKind::FalseEdge { .. }
             | mir::TerminatorKind::FalseUnwind { .. }
diff --git a/compiler/rustc_const_eval/src/interpret/terminator.rs b/compiler/rustc_const_eval/src/interpret/terminator.rs
index 68acddf63d8..7d1a48d6ded 100644
--- a/compiler/rustc_const_eval/src/interpret/terminator.rs
+++ b/compiler/rustc_const_eval/src/interpret/terminator.rs
@@ -172,6 +172,8 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                 }
             }
 
+            TailCall { func: _, args: _, fn_span: _ } => todo!(),
+
             Drop { place, target, unwind, replace: _ } => {
                 let place = self.eval_place(place)?;
                 let instance = Instance::resolve_drop_in_place(*self.tcx, place.layout.ty);
-- 
cgit 1.4.1-3-g733a5