copy arguments

Author: tmiasko

compiler/rustc_mir_transform/src/copy_args.rs

@@ -0,0 +1,35 @@
+use rustc_middle::mir::*;
+use rustc_middle::ty::TyCtxt;
+use rustc_session::config::OptLevel;
+
+pub(super) struct CopyArgs;
+
+impl<'tcx> crate::MirPass<'tcx> for CopyArgs {
+    fn is_enabled(&self, sess: &rustc_session::Session) -> bool {
+        sess.opts.optimize != OptLevel::No && sess.opts.incremental.is_none()
+    }
+
+    fn run_pass(&self, _: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
+        for (_, block) in body.basic_blocks.as_mut_preserves_cfg().iter_enumerated_mut() {
+            if let TerminatorKind::Call { ref mut args, .. } = block.terminator_mut().kind {
+                for arg in args {
+                    if let Operand::Move(place) = arg.node {
+                        if place.is_indirect() {
+                            continue;
+                        }
+                        let Some(local) = place.as_local() else {
+                            continue
+                        };
+                        if 1 <= local.index() && local.index() <= body.arg_count {
+                            arg.node = Operand::Copy(place);
+                        }
+                    }
+                }
+            };
+        }
+    }
+
+    fn is_required(&self) -> bool {
+        false
+    }
+}

compiler/rustc_mir_transform/src/lib.rs

@@ -127,6 +127,7 @@ declare_passes! {
     // This pass is public to allow external drivers to perform MIR cleanup
     pub mod cleanup_post_borrowck : CleanupPostBorrowck;
 
+    mod copy_args : CopyArgs;
     mod copy_prop : CopyProp;
     mod coroutine : StateTransform;
     mod coverage : InstrumentCoverage;
@@ -725,6 +726,7 @@ fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
             &large_enums::EnumSizeOpt { discrepancy: 128 },
             // Some cleanup necessary at least for LLVM and potentially other codegen backends.
             &add_call_guards::CriticalCallEdges,
+            &copy_args::CopyArgs,
             // Cleanup for human readability, off by default.
             &prettify::ReorderBasicBlocks,
             &prettify::ReorderLocals,