Auto merge of rust-lang#128299 - DianQK:clone-copy, r=<try>

Simplify the canonical clone method and the copy-like forms to copy

Fixes rust-lang#128081.

r? `@cjgillot`

compiler/rustc_mir_transform/src/gvn.rs

@@ -863,9 +863,10 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
         rvalue: &mut Rvalue<'tcx>,
         location: Location,
     ) -> Option<VnIndex> {
+        let tcx = self.tcx;
+        let rvalue_ty = rvalue.ty(self.local_decls, tcx);
         let Rvalue::Aggregate(box ref kind, ref mut field_ops) = *rvalue else { bug!() };
 
-        let tcx = self.tcx;
         if field_ops.is_empty() {
             let is_zst = match *kind {
                 AggregateKind::Array(..)
@@ -880,8 +881,7 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
             };
 
             if is_zst {
-                let ty = rvalue.ty(self.local_decls, tcx);
-                return self.insert_constant(Const::zero_sized(ty));
+                return self.insert_constant(Const::zero_sized(rvalue_ty));
             }
         }
 
@@ -916,6 +916,60 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
             .collect();
         let mut fields = fields?;
 
+        if let AggregateTy::Def(_, _) = &mut ty
+            && !fields.is_empty()
+        {
+            let copy_from = if let Value::Projection(first_pointer, ProjectionElem::Field(_, _)) =
+                *self.get(fields[0])
+            {
+                let mut copy_from_value = first_pointer;
+                while let Value::Projection(pointer, ProjectionElem::Deref) =
+                    *self.get(copy_from_value)
+                {
+                    copy_from_value = pointer;
+                }
+                if let Some(local) = self.try_as_local(copy_from_value, location) {
+                    let from_ty = self.local_decls[local].ty;
+                    if rvalue_ty == from_ty {
+                        Some((first_pointer, local, false))
+                    } else if Some(rvalue_ty) == from_ty.builtin_deref(false) {
+                        Some((first_pointer, local, true))
+                    } else {
+                        None
+                    }
+                } else {
+                    None
+                }
+            } else {
+                None
+            };
+            if let Some((first_pointer, local, need_deref)) = copy_from {
+                // All fields must correspond one-to-one and come from the same aggregate value.
+                if std::iter::zip(field_ops.iter_enumerated(), fields.iter()).all(
+                    |((index, _), &v)| {
+                        if let Value::Projection(pointer, ProjectionElem::Field(from_index, _)) =
+                            *self.get(v)
+                            && first_pointer == pointer
+                            && from_index == index
+                        {
+                            return true;
+                        }
+                        false
+                    },
+                ) {
+                    *rvalue = Rvalue::Use(Operand::Copy(Place {
+                        local,
+                        projection: tcx.mk_place_elems(if need_deref {
+                            &[ProjectionElem::Deref]
+                        } else {
+                            &[]
+                        }),
+                    }));
+                    return Some(first_pointer);
+                }
+            }
+        }
+
         if let AggregateTy::RawPtr { data_pointer_ty, output_pointer_ty } = &mut ty {
             let mut was_updated = false;
 

tests/codegen/clone_as_copy.rs

@@ -0,0 +1,40 @@
+//@ revisions: DEBUGINFO NODEBUGINFO
+//@ compile-flags: -O -Cno-prepopulate-passes
+//@ [DEBUGINFO] compile-flags: -Cdebuginfo=full
+
+// From https://github.com/rust-lang/rust/issues/128081.
+// Ensure that we only generate a memcpy instruction.
+
+#![crate_type = "lib"]
+
+#[derive(Clone)]
+struct SubCloneAndCopy {
+    v1: u32,
+    v2: u32,
+}
+
+#[derive(Clone)]
+struct CloneOnly {
+    v1: u8,
+    v2: u8,
+    v3: u8,
+    v4: u8,
+    v5: u8,
+    v6: u8,
+    v7: u8,
+    v8: u8,
+    v9: u8,
+    v_sub: SubCloneAndCopy,
+    v_large: [u8; 256],
+}
+
+// CHECK-LABEL: define {{.*}}@clone_only(
+#[no_mangle]
+pub fn clone_only(v: &CloneOnly) -> CloneOnly {
+    // CHECK-NOT: call {{.*}}clone
+    // CHECK-NOT: store i8
+    // CHECK-NOT: store i32
+    // CHECK: call void @llvm.memcpy
+    // CHECK-NEXT: ret void
+    v.clone()
+}

tests/mir-opt/gvn_clone.rs

@@ -0,0 +1,17 @@
+//@ test-mir-pass: GVN
+//@ compile-flags: -Zmir-enable-passes=+InstSimplify-before-inline
+
+// Check if we have transformed the default clone to copy in the specific pipeline.
+
+// EMIT_MIR gvn_clone.{impl#0}-clone.GVN.diff
+
+// CHECK-LABEL: ::clone(
+// CHECK-NOT: = AllCopy { {{.*}} };
+// CHECK: _0 = (*_1);
+// CHECK: return;
+#[derive(Clone)]
+struct AllCopy {
+    a: i32,
+    b: u64,
+    c: [i8; 3],
+}

tests/mir-opt/gvn_clone.{impl#0}-clone.GVN.diff

@@ -0,0 +1,71 @@
+- // MIR for `<impl at $DIR/gvn_clone.rs:12:10: 12:15>::clone` before GVN
++ // MIR for `<impl at $DIR/gvn_clone.rs:12:10: 12:15>::clone` after GVN
+
+  fn <impl at $DIR/gvn_clone.rs:12:10: 12:15>::clone(_1: &AllCopy) -> AllCopy {
+      debug self => _1;
+      let mut _0: AllCopy;
+      let mut _2: i32;
+      let mut _3: &i32;
+      let _4: &i32;
+      let mut _5: u64;
+      let mut _6: &u64;
+      let _7: &u64;
+      let mut _8: [i8; 3];
+      let mut _9: &[i8; 3];
+      let _10: &[i8; 3];
+
+      bb0: {
+          StorageLive(_2);
+          StorageLive(_3);
+-         StorageLive(_4);
++         nop;
+          _4 = &((*_1).0: i32);
+          _3 = _4;
+-         _2 = (*_3);
++         _2 = ((*_1).0: i32);
+          goto -> bb1;
+      }
+
+      bb1: {
+          StorageDead(_3);
+          StorageLive(_5);
+          StorageLive(_6);
+-         StorageLive(_7);
++         nop;
+          _7 = &((*_1).1: u64);
+          _6 = _7;
+-         _5 = (*_6);
++         _5 = ((*_1).1: u64);
+          goto -> bb2;
+      }
+
+      bb2: {
+          StorageDead(_6);
+          StorageLive(_8);
+          StorageLive(_9);
+-         StorageLive(_10);
++         nop;
+          _10 = &((*_1).2: [i8; 3]);
+          _9 = _10;
+-         _8 = (*_9);
++         _8 = ((*_1).2: [i8; 3]);
+          goto -> bb3;
+      }
+
+      bb3: {
+          StorageDead(_9);
+-         _0 = AllCopy { a: move _2, b: move _5, c: move _8 };
++         _0 = (*_1);
+          StorageDead(_8);
+          StorageDead(_5);
+          StorageDead(_2);
+-         StorageDead(_10);
+-         StorageDead(_7);
+-         StorageDead(_4);
++         nop;
++         nop;
++         nop;
+          return;
+      }
+  }
+

tests/mir-opt/gvn_copy_aggregate.all_copy.GVN.diff

@@ -0,0 +1,53 @@
+- // MIR for `all_copy` before GVN
++ // MIR for `all_copy` after GVN
+
+  fn all_copy(_1: &AllCopy) -> AllCopy {
+      debug v => _1;
+      let mut _0: AllCopy;
+      let _2: i32;
+      let mut _5: i32;
+      let mut _6: u64;
+      let mut _7: [i8; 3];
+      scope 1 {
+          debug a => _2;
+          let _3: u64;
+          scope 2 {
+              debug b => _3;
+              let _4: [i8; 3];
+              scope 3 {
+                  debug c => _4;
+              }
+          }
+      }
+
+      bb0: {
+-         StorageLive(_2);
++         nop;
+          _2 = ((*_1).0: i32);
+-         StorageLive(_3);
++         nop;
+          _3 = ((*_1).1: u64);
+-         StorageLive(_4);
++         nop;
+          _4 = ((*_1).2: [i8; 3]);
+          StorageLive(_5);
+          _5 = _2;
+          StorageLive(_6);
+          _6 = _3;
+          StorageLive(_7);
+          _7 = _4;
+-         _0 = AllCopy { a: move _5, b: move _6, c: move _7 };
++         _0 = (*_1);
+          StorageDead(_7);
+          StorageDead(_6);
+          StorageDead(_5);
+-         StorageDead(_4);
+-         StorageDead(_3);
+-         StorageDead(_2);
++         nop;
++         nop;
++         nop;
+          return;
+      }
+  }
+

tests/mir-opt/gvn_copy_aggregate.all_copy_different_type.GVN.diff

@@ -0,0 +1,53 @@
+- // MIR for `all_copy_different_type` before GVN
++ // MIR for `all_copy_different_type` after GVN
+
+  fn all_copy_different_type(_1: &AllCopy) -> AllCopy2 {
+      debug v => _1;
+      let mut _0: AllCopy2;
+      let _2: i32;
+      let mut _5: i32;
+      let mut _6: u64;
+      let mut _7: [i8; 3];
+      scope 1 {
+          debug a => _2;
+          let _3: u64;
+          scope 2 {
+              debug b => _3;
+              let _4: [i8; 3];
+              scope 3 {
+                  debug c => _4;
+              }
+          }
+      }
+
+      bb0: {
+-         StorageLive(_2);
++         nop;
+          _2 = ((*_1).0: i32);
+-         StorageLive(_3);
++         nop;
+          _3 = ((*_1).1: u64);
+-         StorageLive(_4);
++         nop;
+          _4 = ((*_1).2: [i8; 3]);
+          StorageLive(_5);
+          _5 = _2;
+          StorageLive(_6);
+          _6 = _3;
+          StorageLive(_7);
+          _7 = _4;
+-         _0 = AllCopy2 { a: move _5, b: move _6, c: move _7 };
++         _0 = AllCopy2 { a: _2, b: _3, c: _4 };
+          StorageDead(_7);
+          StorageDead(_6);
+          StorageDead(_5);
+-         StorageDead(_4);
+-         StorageDead(_3);
+-         StorageDead(_2);
++         nop;
++         nop;
++         nop;
+          return;
+      }
+  }
+

tests/mir-opt/gvn_copy_aggregate.all_copy_has_changed.GVN.diff

@@ -0,0 +1,54 @@
+- // MIR for `all_copy_has_changed` before GVN
++ // MIR for `all_copy_has_changed` after GVN
+
+  fn all_copy_has_changed(_1: &mut AllCopy) -> AllCopy {
+      debug v => _1;
+      let mut _0: AllCopy;
+      let _2: i32;
+      let mut _5: i32;
+      let mut _6: u64;
+      let mut _7: [i8; 3];
+      scope 1 {
+          debug a => _2;
+          let _3: u64;
+          scope 2 {
+              debug b => _3;
+              let _4: [i8; 3];
+              scope 3 {
+                  debug c => _4;
+              }
+          }
+      }
+
+      bb0: {
+-         StorageLive(_2);
++         nop;
+          _2 = ((*_1).0: i32);
+-         StorageLive(_3);
++         nop;
+          _3 = ((*_1).1: u64);
+-         StorageLive(_4);
++         nop;
+          _4 = ((*_1).2: [i8; 3]);
+          ((*_1).0: i32) = const 1_i32;
+          StorageLive(_5);
+          _5 = _2;
+          StorageLive(_6);
+          _6 = _3;
+          StorageLive(_7);
+          _7 = _4;
+-         _0 = AllCopy { a: move _5, b: move _6, c: move _7 };
++         _0 = AllCopy { a: _2, b: _3, c: _4 };
+          StorageDead(_7);
+          StorageDead(_6);
+          StorageDead(_5);
+-         StorageDead(_4);
+-         StorageDead(_3);
+-         StorageDead(_2);
++         nop;
++         nop;
++         nop;
+          return;
+      }
+  }
+