Rollup merge of #116277 - RalfJung:post-mono, r=oli-obk

dont call mir.post_mono_checks in codegen

It seems like all tests are still passing when I remove this... let's see what CI says.

2 files changed, 6 insertions, 11 deletions

diff --git a/compiler/rustc_codegen_ssa/src/mir/constant.rs b/compiler/rustc_codegen_ssa/src/mir/constant.rs
index fde4e85f966..558f64fffc2 100644
--- a/compiler/rustc_codegen_ssa/src/mir/constant.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/constant.rs
@@ -21,6 +21,8 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
     }
 
     pub fn eval_mir_constant(&self, constant: &mir::ConstOperand<'tcx>) -> mir::ConstValue<'tcx> {
+        // `MirUsedCollector` visited all constants before codegen began, so if we got here there
+        // can be no more constants that fail to evaluate.
         self.monomorphize(constant.const_)
             .eval(self.cx.tcx(), ty::ParamEnv::reveal_all(), Some(constant.span))
             .expect("erroneous constant not captured by required_consts")
diff --git a/compiler/rustc_codegen_ssa/src/mir/mod.rs b/compiler/rustc_codegen_ssa/src/mir/mod.rs
index a61018f9870..d0b799e087b 100644
--- a/compiler/rustc_codegen_ssa/src/mir/mod.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/mod.rs
@@ -209,18 +209,11 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
         caller_location: None,
     };
 
-    fx.per_local_var_debug_info = fx.compute_per_local_var_debug_info(&mut start_bx);
+    // It may seem like we should iterate over `required_consts` to ensure they all successfully
+    // evaluate; however, the `MirUsedCollector` already did that during the collection phase of
+    // monomorphization so we don't have to do it again.
 
-    // Rust post-monomorphization checks; we later rely on them.
-    if let Err(err) =
-        mir.post_mono_checks(cx.tcx(), ty::ParamEnv::reveal_all(), |c| Ok(fx.monomorphize(c)))
-    {
-        err.emit_err(cx.tcx());
-        // This IR shouldn't ever be emitted, but let's try to guard against any of this code
-        // ever running.
-        start_bx.abort();
-        return;
-    }
+    fx.per_local_var_debug_info = fx.compute_per_local_var_debug_info(&mut start_bx);
 
     let memory_locals = analyze::non_ssa_locals(&fx);