Auto merge of #142890 - kornelski:unused-var-debug, r=saethlin

MIR inliner maintains unused var_debug_info

Only `full` debuginfo level promises variable-level debug information, but the MIR inline pass needlessly preserved the local variable debug info for the `limited` level too.

1 files changed, 4 insertions, 2 deletions

diff --git a/compiler/rustc_mir_transform/src/inline.rs b/compiler/rustc_mir_transform/src/inline.rs
index 7852bb7ae2f..1c0fc774867 100644
--- a/compiler/rustc_mir_transform/src/inline.rs
+++ b/compiler/rustc_mir_transform/src/inline.rs
@@ -982,14 +982,16 @@ fn inline_call<'tcx, I: Inliner<'tcx>>(
     // Insert all of the (mapped) parts of the callee body into the caller.
     caller_body.local_decls.extend(callee_body.drain_vars_and_temps());
     caller_body.source_scopes.append(&mut callee_body.source_scopes);
+
+    // only "full" debug promises any variable-level information
     if tcx
         .sess
         .opts
         .unstable_opts
         .inline_mir_preserve_debug
-        .unwrap_or(tcx.sess.opts.debuginfo != DebugInfo::None)
+        .unwrap_or(tcx.sess.opts.debuginfo == DebugInfo::Full)
     {
-        // Note that we need to preserve these in the standard library so that
+        // -Zinline-mir-preserve-debug is enabled when building the standard library, so that
         // people working on rust can build with or without debuginfo while
         // still getting consistent results from the mir-opt tests.
         caller_body.var_debug_info.append(&mut callee_body.var_debug_info);