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

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());

tests/mir-opt/instsimplify/casts.rs

@@ -1,6 +1,7 @@
 //@ test-mir-pass: InstSimplify
 //@ compile-flags: -Zinline-mir
 #![crate_type = "lib"]
+#![feature(core_intrinsics)]
 
 #[inline(always)]
 fn generic_cast<T, U>(x: *const T) -> *const U {
@@ -23,3 +24,11 @@ pub fn roundtrip(x: *const u8) -> *const u8 {
     // CHECK: _2 = move _3 as *const u8 (PointerCoercion(MutToConstPointer));
     x as *mut u8 as *const u8
 }
+
+// EMIT_MIR casts.roundtrip.InstSimplify.diff
+pub fn cast_thin_via_aggregate(x: *const u8) -> *const () {
+    // CHECK-LABEL: fn cast_thin_via_aggregate(
+    // CHECK: _2 = _1;
+    // CHECK: _0 = move _2 as *const () (PtrToPtr);
+    std::intrinsics::aggregate_raw_ptr(x, ())
+}

tests/mir-opt/pre-codegen/ptr_offset.demo_byte_add_fat.PreCodegen.after.panic-abort.mir

@@ -28,8 +28,6 @@ fn demo_byte_add_fat(_1: *const [u32], _2: usize) -> *const [u32] {
             scope 6 (inlined std::ptr::from_raw_parts::<[u32]>) {
                 debug data_pointer => _5;
                 debug metadata => _7;
-                let mut _8: std::ptr::metadata::PtrComponents<[u32]>;
-                let mut _9: std::ptr::metadata::PtrRepr<[u32]>;
             }
         }
     }
@@ -47,13 +45,7 @@ fn demo_byte_add_fat(_1: *const [u32], _2: usize) -> *const [u32] {
         _6 = std::ptr::metadata::PtrRepr::<[u32]> { const_ptr: _1 };
         _7 = ((_6.2: std::ptr::metadata::PtrComponents<[u32]>).1: usize);
         StorageDead(_6);
-        StorageLive(_9);
+        _0 = *const [u32] from (_5, _7);
-        StorageLive(_8);
-        _8 = std::ptr::metadata::PtrComponents::<[u32]> { data_pointer: _5, metadata: _7 };
-        _9 = std::ptr::metadata::PtrRepr::<[u32]> { const_ptr: move _8 };
-        StorageDead(_8);
-        _0 = (_9.0: *const [u32]);
-        StorageDead(_9);
         StorageDead(_7);
         StorageDead(_5);
         StorageDead(_4);

tests/mir-opt/pre-codegen/ptr_offset.demo_byte_add_fat.PreCodegen.after.panic-unwind.mir

@@ -28,8 +28,6 @@ fn demo_byte_add_fat(_1: *const [u32], _2: usize) -> *const [u32] {
             scope 6 (inlined std::ptr::from_raw_parts::<[u32]>) {
                 debug data_pointer => _5;
                 debug metadata => _7;
-                let mut _8: std::ptr::metadata::PtrComponents<[u32]>;
-                let mut _9: std::ptr::metadata::PtrRepr<[u32]>;
             }
         }
     }
@@ -47,13 +45,7 @@ fn demo_byte_add_fat(_1: *const [u32], _2: usize) -> *const [u32] {
         _6 = std::ptr::metadata::PtrRepr::<[u32]> { const_ptr: _1 };
         _7 = ((_6.2: std::ptr::metadata::PtrComponents<[u32]>).1: usize);
         StorageDead(_6);
-        StorageLive(_9);
+        _0 = *const [u32] from (_5, _7);
-        StorageLive(_8);
-        _8 = std::ptr::metadata::PtrComponents::<[u32]> { data_pointer: _5, metadata: _7 };
-        _9 = std::ptr::metadata::PtrRepr::<[u32]> { const_ptr: move _8 };
-        StorageDead(_8);
-        _0 = (_9.0: *const [u32]);
-        StorageDead(_9);
         StorageDead(_7);
         StorageDead(_5);
         StorageDead(_4);

tests/mir-opt/pre-codegen/ptr_offset.demo_byte_add_thin.PreCodegen.after.panic-abort.mir

@@ -26,29 +26,19 @@ fn demo_byte_add_thin(_1: *const u32, _2: usize) -> *const u32 {
             scope 6 (inlined std::ptr::from_raw_parts::<u32>) {
                 debug data_pointer => _5;
                 debug metadata => const ();
-                let mut _6: std::ptr::metadata::PtrComponents<u32>;
-                let mut _7: std::ptr::metadata::PtrRepr<u32>;
             }
         }
     }
 
     bb0: {
-        StorageLive(_4);
         StorageLive(_3);
         _3 = _1 as *const u8 (PtrToPtr);
         _4 = Offset(_3, _2);
         StorageDead(_3);
         StorageLive(_5);
         _5 = _4 as *const () (PtrToPtr);
-        StorageLive(_7);
+        _0 = _4 as *const u32 (PtrToPtr);
-        StorageLive(_6);
-        _6 = std::ptr::metadata::PtrComponents::<u32> { data_pointer: _5, metadata: const () };
-        _7 = std::ptr::metadata::PtrRepr::<u32> { const_ptr: move _6 };
-        StorageDead(_6);
-        _0 = (_7.0: *const u32);
-        StorageDead(_7);
         StorageDead(_5);
-        StorageDead(_4);
         return;
     }
 }

tests/mir-opt/pre-codegen/ptr_offset.demo_byte_add_thin.PreCodegen.after.panic-unwind.mir

@@ -26,29 +26,19 @@ fn demo_byte_add_thin(_1: *const u32, _2: usize) -> *const u32 {
             scope 6 (inlined std::ptr::from_raw_parts::<u32>) {
                 debug data_pointer => _5;
                 debug metadata => const ();
-                let mut _6: std::ptr::metadata::PtrComponents<u32>;
-                let mut _7: std::ptr::metadata::PtrRepr<u32>;
             }
         }
     }
 
     bb0: {
-        StorageLive(_4);
         StorageLive(_3);
         _3 = _1 as *const u8 (PtrToPtr);
         _4 = Offset(_3, _2);
         StorageDead(_3);
         StorageLive(_5);
         _5 = _4 as *const () (PtrToPtr);
-        StorageLive(_7);
+        _0 = _4 as *const u32 (PtrToPtr);
-        StorageLive(_6);
-        _6 = std::ptr::metadata::PtrComponents::<u32> { data_pointer: _5, metadata: const () };
-        _7 = std::ptr::metadata::PtrRepr::<u32> { const_ptr: move _6 };
-        StorageDead(_6);
-        _0 = (_7.0: *const u32);
-        StorageDead(_7);
         StorageDead(_5);
-        StorageDead(_4);
         return;
     }
 }