Rollup merge of #120773 - Enselic:copy-vs-move, r=oli-obk

large_assignments: Allow moves into functions

Moves into functions are typically implemented with pointer passing
rather than memcpy's at the llvm-ir level, so allow moves into
functions.

Part of the "Differentiate between Operand::Move and Operand::Copy" step of https://github.com/rust-lang/rust/issues/83518.

r? `@oli-obk` (who I think is still E-mentor?)

1 files changed, 9 insertions, 1 deletions

diff --git a/compiler/rustc_monomorphize/src/collector.rs b/compiler/rustc_monomorphize/src/collector.rs
index 3376af98653..149e4c2cb08 100644
--- a/compiler/rustc_monomorphize/src/collector.rs
+++ b/compiler/rustc_monomorphize/src/collector.rs
@@ -666,7 +666,15 @@ impl<'a, 'tcx> MirUsedCollector<'a, 'tcx> {
         debug!(?def_id, ?fn_span);
 
         for arg in args {
-            if let Some(too_large_size) = self.operand_size_if_too_large(limit, &arg.node) {
+            // Moving args into functions is typically implemented with pointer
+            // passing at the llvm-ir level and not by memcpy's. So always allow
+            // moving args into functions.
+            let operand: &mir::Operand<'tcx> = &arg.node;
+            if let mir::Operand::Move(_) = operand {
+                continue;
+            }
+
+            if let Some(too_large_size) = self.operand_size_if_too_large(limit, operand) {
                 self.lint_large_assignment(limit.0, too_large_size, location, arg.span);
             };
         }