InstSimplify `from_raw_parts(p, ())` → `p as _`

1 files changed, 35 insertions, 1 deletions

diff --git a/compiler/rustc_mir_transform/src/instsimplify.rs b/compiler/rustc_mir_transform/src/instsimplify.rs
index ff786d44d6a..bae959963b5 100644
--- a/compiler/rustc_mir_transform/src/instsimplify.rs
+++ b/compiler/rustc_mir_transform/src/instsimplify.rs
@@ -36,6 +36,7 @@ impl<'tcx> MirPass<'tcx> for InstSimplify {
                         ctx.simplify_bool_cmp(&statement.source_info, rvalue);
                         ctx.simplify_ref_deref(&statement.source_info, rvalue);
                         ctx.simplify_len(&statement.source_info, rvalue);
+                        ctx.simplify_ptr_aggregate(&statement.source_info, rvalue);
                         ctx.simplify_cast(rvalue);
                     }
                     _ => {}
@@ -58,8 +59,17 @@ struct InstSimplifyContext<'tcx, 'a> {
 
 impl<'tcx> InstSimplifyContext<'tcx, '_> {
     fn should_simplify(&self, source_info: &SourceInfo, rvalue: &Rvalue<'tcx>) -> bool {
+        self.should_simplify_custom(source_info, "Rvalue", rvalue)
+    }
+
+    fn should_simplify_custom(
+        &self,
+        source_info: &SourceInfo,
+        label: &str,
+        value: impl std::fmt::Debug,
+    ) -> bool {
         self.tcx.consider_optimizing(|| {
-            format!("InstSimplify - Rvalue: {rvalue:?} SourceInfo: {source_info:?}")
+            format!("InstSimplify - {label}: {value:?} SourceInfo: {source_info:?}")
         })
     }
 
@@ -147,6 +157,30 @@ impl<'tcx> InstSimplifyContext<'tcx, '_> {
         }
     }
 
+    /// Transform "Aggregate(RawPtr, \[p, ()\])" ==> "Cast(PtrToPtr, p)".
+    fn simplify_ptr_aggregate(&self, source_info: &SourceInfo, rvalue: &mut Rvalue<'tcx>) {
+        if let Rvalue::Aggregate(box AggregateKind::RawPtr(pointee_ty, mutability), fields) = rvalue
+        {
+            let meta_ty = fields.raw[1].ty(self.local_decls, self.tcx);
+            if meta_ty.is_unit() {
+                // The mutable borrows we're holding prevent printing `rvalue` here
+                if !self.should_simplify_custom(
+                    source_info,
+                    "Aggregate::RawPtr",
+                    (&pointee_ty, *mutability, &fields),
+                ) {
+                    return;
+                }
+
+                let mut fields = std::mem::take(fields);
+                let _meta = fields.pop().unwrap();
+                let data = fields.pop().unwrap();
+                let ptr_ty = Ty::new_ptr(self.tcx, *pointee_ty, *mutability);
+                *rvalue = Rvalue::Cast(CastKind::PtrToPtr, data, ptr_ty);
+            }
+        }
+    }
+
     fn simplify_ub_check(&self, source_info: &SourceInfo, rvalue: &mut Rvalue<'tcx>) {
         if let Rvalue::NullaryOp(NullOp::UbChecks, _) = *rvalue {
             let const_ = Const::from_bool(self.tcx, self.tcx.sess.ub_checks());