Remove bounds check when array is indexed by enum

compiler/rustc_mir_build/src/build/expr/as_rvalue.rs

@@ -2,6 +2,7 @@
 
 use rustc_index::vec::Idx;
 use rustc_middle::ty::util::IntTypeExt;
+use rustc_target::abi::{Abi, Primitive};
 
 use crate::build::expr::as_place::PlaceBase;
 use crate::build::expr::category::{Category, RvalueFunc};
@@ -198,15 +199,63 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 let (source, ty) = if let ty::Adt(adt_def, ..) = source.ty.kind() && adt_def.is_enum() {
                     let discr_ty = adt_def.repr().discr_type().to_ty(this.tcx);
                     let temp = unpack!(block = this.as_temp(block, scope, source, Mutability::Not));
+                    let layout = this.tcx.layout_of(this.param_env.and(source.ty));
                     let discr = this.temp(discr_ty, source.span);
                     this.cfg.push_assign(
                         block,
                         source_info,
                         discr,
                         Rvalue::Discriminant(temp.into()),
                     );
+                    let (op,ty) = (Operand::Move(discr), discr_ty);
+
+                    if let Abi::Scalar(scalar) = layout.unwrap().abi{
+                        if let Primitive::Int(_, signed) = scalar.primitive() {
+                            let range = scalar.valid_range(&this.tcx);
+                            // FIXME: Handle wraparound cases too.
+                            if range.end >= range.start {
+                                let mut assumer = |range: u128, bin_op: BinOp| {
+                                    // We will be overwriting this val if our scalar is signed value
+                                    // because sign extension on unsigned types might cause unintended things
+                                    let mut range_val =
+                                        ConstantKind::from_bits(this.tcx, range, ty::ParamEnv::empty().and(discr_ty));
+                                    let bool_ty = this.tcx.types.bool;
+                                    if signed {
+                                        let scalar_size_extend = scalar.size(&this.tcx).sign_extend(range);
+                                        let discr_layout = this.tcx.layout_of(this.param_env.and(discr_ty));
+                                        let truncated_val = discr_layout.unwrap().size.truncate(scalar_size_extend);
+                                        range_val = ConstantKind::from_bits(
+                                            this.tcx,
+                                            truncated_val,
+                                            ty::ParamEnv::empty().and(discr_ty),
+                                        );
+                                    }
+                                    let lit_op = this.literal_operand(expr.span, range_val);
+                                    let is_bin_op = this.temp(bool_ty, expr_span);
+                                    this.cfg.push_assign(
+                                        block,
+                                        source_info,
+                                        is_bin_op,
+                                        Rvalue::BinaryOp(bin_op, Box::new(((lit_op), (Operand::Copy(discr))))),
+                                    );
+                                    this.cfg.push(
+                                        block,
+                                        Statement {
+                                            source_info,
+                                            kind: StatementKind::Intrinsic(Box::new(NonDivergingIntrinsic::Assume(
+                                                Operand::Copy(is_bin_op),
+                                            ))),
+                                        },
+                                    )
+                                };
+                                assumer(range.end, BinOp::Ge);
+                                assumer(range.start, BinOp::Le);
+                            }
+                        }
+                    }
+
+                    (op,ty)
 
-                    (Operand::Move(discr), discr_ty)
                 } else {
                     let ty = source.ty;
                     let source = unpack!(

compiler/rustc_mir_transform/src/check_unsafety.rs

@@ -101,12 +101,10 @@ impl<'tcx> Visitor<'tcx> for UnsafetyChecker<'_, 'tcx> {
             | StatementKind::Retag { .. }
             | StatementKind::AscribeUserType(..)
             | StatementKind::Coverage(..)
+            | StatementKind::Intrinsic(..)
             | StatementKind::Nop => {
                 // safe (at least as emitted during MIR construction)
             }
-
-            // Move to above list once mir construction uses it.
-            StatementKind::Intrinsic(..) => unreachable!(),
         }
         self.super_statement(statement, location);
     }

src/test/codegen/enum-bounds-check-derived-idx.rs

@@ -12,15 +12,13 @@ pub enum Bar {
 // CHECK-LABEL: @lookup_inc
 #[no_mangle]
 pub fn lookup_inc(buf: &[u8; 5], f: Bar) -> u8 {
-    // FIXME: panic check can be removed by adding the assumes back after https://github.com/rust-lang/rust/pull/98332
-    // CHECK: panic_bounds_check
+    // CHECK-NOT: panic_bounds_check
     buf[f as usize + 1]
 }
 
 // CHECK-LABEL: @lookup_dec
 #[no_mangle]
 pub fn lookup_dec(buf: &[u8; 5], f: Bar) -> u8 {
-    // FIXME: panic check can be removed by adding the assumes back after https://github.com/rust-lang/rust/pull/98332
-    // CHECK: panic_bounds_check
+    // CHECK-NOT: panic_bounds_check
     buf[f as usize - 1]
 }

src/test/codegen/enum-bounds-check-issue-13926.rs

@@ -13,7 +13,6 @@ pub enum Exception {
 // CHECK-LABEL: @access
 #[no_mangle]
 pub fn access(array: &[usize; 12], exc: Exception) -> usize {
-    // FIXME: panic check can be removed by adding the assumes back after https://github.com/rust-lang/rust/pull/98332
-    // CHECK: panic_bounds_check
+    // CHECK-NOT: panic_bounds_check
     array[(exc as u8 - 4) as usize]
 }

src/test/codegen/enum-bounds-check.rs

@@ -21,7 +21,6 @@ pub enum Bar {
 // CHECK-LABEL: @lookup_unmodified
 #[no_mangle]
 pub fn lookup_unmodified(buf: &[u8; 5], f: Bar) -> u8 {
-    // FIXME: panic check can be removed by adding the assumes back after https://github.com/rust-lang/rust/pull/98332
-    // CHECK: panic_bounds_check
+    // CHECK-NOT: panic_bounds_check
     buf[f as usize]
 }

src/test/mir-opt/building/enum_cast.bar.built.after.mir

@@ -5,11 +5,17 @@ fn bar(_1: Bar) -> usize {
     let mut _0: usize;                   // return place in scope 0 at $DIR/enum_cast.rs:+0:21: +0:26
     let _2: Bar;                         // in scope 0 at $DIR/enum_cast.rs:+1:5: +1:8
     let mut _3: isize;                   // in scope 0 at $DIR/enum_cast.rs:+1:5: +1:8
+    let mut _4: bool;                    // in scope 0 at $DIR/enum_cast.rs:+1:5: +1:17
+    let mut _5: bool;                    // in scope 0 at $DIR/enum_cast.rs:+1:5: +1:17
 
     bb0: {
         StorageLive(_2);                 // scope 0 at $DIR/enum_cast.rs:+1:5: +1:8
         _2 = move _1;                    // scope 0 at $DIR/enum_cast.rs:+1:5: +1:8
         _3 = discriminant(_2);           // scope 0 at $DIR/enum_cast.rs:+1:5: +1:17
+        _4 = Ge(const 1_isize, _3);      // scope 0 at $DIR/enum_cast.rs:+1:5: +1:17
+        assume(_4);                      // scope 0 at $DIR/enum_cast.rs:+1:5: +1:17
+        _5 = Le(const 0_isize, _3);      // scope 0 at $DIR/enum_cast.rs:+1:5: +1:17
+        assume(_5);                      // scope 0 at $DIR/enum_cast.rs:+1:5: +1:17
         _0 = move _3 as usize (IntToInt); // scope 0 at $DIR/enum_cast.rs:+1:5: +1:17
         StorageDead(_2);                 // scope 0 at $DIR/enum_cast.rs:+1:16: +1:17
         return;                          // scope 0 at $DIR/enum_cast.rs:+2:2: +2:2

src/test/mir-opt/building/enum_cast.boo.built.after.mir

@@ -5,11 +5,17 @@ fn boo(_1: Boo) -> usize {
     let mut _0: usize;                   // return place in scope 0 at $DIR/enum_cast.rs:+0:21: +0:26
     let _2: Boo;                         // in scope 0 at $DIR/enum_cast.rs:+1:5: +1:8
     let mut _3: u8;                      // in scope 0 at $DIR/enum_cast.rs:+1:5: +1:8
+    let mut _4: bool;                    // in scope 0 at $DIR/enum_cast.rs:+1:5: +1:17
+    let mut _5: bool;                    // in scope 0 at $DIR/enum_cast.rs:+1:5: +1:17
 
     bb0: {
         StorageLive(_2);                 // scope 0 at $DIR/enum_cast.rs:+1:5: +1:8
         _2 = move _1;                    // scope 0 at $DIR/enum_cast.rs:+1:5: +1:8
         _3 = discriminant(_2);           // scope 0 at $DIR/enum_cast.rs:+1:5: +1:17
+        _4 = Ge(const 1_u8, _3);         // scope 0 at $DIR/enum_cast.rs:+1:5: +1:17
+        assume(_4);                      // scope 0 at $DIR/enum_cast.rs:+1:5: +1:17
+        _5 = Le(const 0_u8, _3);         // scope 0 at $DIR/enum_cast.rs:+1:5: +1:17
+        assume(_5);                      // scope 0 at $DIR/enum_cast.rs:+1:5: +1:17
         _0 = move _3 as usize (IntToInt); // scope 0 at $DIR/enum_cast.rs:+1:5: +1:17
         StorageDead(_2);                 // scope 0 at $DIR/enum_cast.rs:+1:16: +1:17
         return;                          // scope 0 at $DIR/enum_cast.rs:+2:2: +2:2

src/test/mir-opt/building/enum_cast.droppy.built.after.mir

@@ -6,7 +6,9 @@ fn droppy() -> () {
     let _2: Droppy;                      // in scope 0 at $DIR/enum_cast.rs:+2:13: +2:14
     let _4: Droppy;                      // in scope 0 at $DIR/enum_cast.rs:+5:17: +5:18
     let mut _5: isize;                   // in scope 0 at $DIR/enum_cast.rs:+5:17: +5:18
-    let _6: Droppy;                      // in scope 0 at $DIR/enum_cast.rs:+7:9: +7:10
+    let mut _6: bool;                    // in scope 0 at $DIR/enum_cast.rs:+5:17: +5:27
+    let mut _7: bool;                    // in scope 0 at $DIR/enum_cast.rs:+5:17: +5:27
+    let _8: Droppy;                      // in scope 0 at $DIR/enum_cast.rs:+7:9: +7:10
     scope 1 {
         debug x => _2;                   // in scope 1 at $DIR/enum_cast.rs:+2:13: +2:14
         scope 2 {
@@ -17,7 +19,7 @@ fn droppy() -> () {
         }
     }
     scope 4 {
-        debug z => _6;                   // in scope 4 at $DIR/enum_cast.rs:+7:9: +7:10
+        debug z => _8;                   // in scope 4 at $DIR/enum_cast.rs:+7:9: +7:10
     }
 
     bb0: {
@@ -29,6 +31,10 @@ fn droppy() -> () {
         StorageLive(_4);                 // scope 3 at $DIR/enum_cast.rs:+5:17: +5:18
         _4 = move _2;                    // scope 3 at $DIR/enum_cast.rs:+5:17: +5:18
         _5 = discriminant(_4);           // scope 3 at $DIR/enum_cast.rs:+5:17: +5:27
+        _6 = Ge(const 2_isize, _5);      // scope 3 at $DIR/enum_cast.rs:+5:17: +5:27
+        assume(_6);                      // scope 3 at $DIR/enum_cast.rs:+5:17: +5:27
+        _7 = Le(const 0_isize, _5);      // scope 3 at $DIR/enum_cast.rs:+5:17: +5:27
+        assume(_7);                      // scope 3 at $DIR/enum_cast.rs:+5:17: +5:27
         _3 = move _5 as usize (IntToInt); // scope 3 at $DIR/enum_cast.rs:+5:17: +5:27
         drop(_4) -> [return: bb1, unwind: bb4]; // scope 3 at $DIR/enum_cast.rs:+5:26: +5:27
     }
@@ -44,15 +50,15 @@ fn droppy() -> () {
     bb2: {
         StorageDead(_2);                 // scope 0 at $DIR/enum_cast.rs:+6:5: +6:6
         StorageDead(_1);                 // scope 0 at $DIR/enum_cast.rs:+6:5: +6:6
-        StorageLive(_6);                 // scope 0 at $DIR/enum_cast.rs:+7:9: +7:10
-        _6 = Droppy::B;                  // scope 0 at $DIR/enum_cast.rs:+7:13: +7:22
-        FakeRead(ForLet(None), _6);      // scope 0 at $DIR/enum_cast.rs:+7:9: +7:10
+        StorageLive(_8);                 // scope 0 at $DIR/enum_cast.rs:+7:9: +7:10
+        _8 = Droppy::B;                  // scope 0 at $DIR/enum_cast.rs:+7:13: +7:22
+        FakeRead(ForLet(None), _8);      // scope 0 at $DIR/enum_cast.rs:+7:9: +7:10
         _0 = const ();                   // scope 0 at $DIR/enum_cast.rs:+0:13: +8:2
-        drop(_6) -> [return: bb3, unwind: bb5]; // scope 0 at $DIR/enum_cast.rs:+8:1: +8:2
+        drop(_8) -> [return: bb3, unwind: bb5]; // scope 0 at $DIR/enum_cast.rs:+8:1: +8:2
     }
 
     bb3: {
-        StorageDead(_6);                 // scope 0 at $DIR/enum_cast.rs:+8:1: +8:2
+        StorageDead(_8);                 // scope 0 at $DIR/enum_cast.rs:+8:1: +8:2
         return;                          // scope 0 at $DIR/enum_cast.rs:+8:2: +8:2
     }
 

src/test/ui/type-alias-enum-variants/self-in-enum-definition.stderr

@@ -12,6 +12,46 @@ LL |     V3 = Self::V1 {} as u8 + 2,
 note: ...which requires const-evaluating + checking `Alpha::V3::{constant#0}`...
   --> $DIR/self-in-enum-definition.rs:5:10
    |
+LL |     V3 = Self::V1 {} as u8 + 2,
+   |          ^^^^^^^^^^^^^^^^^^^^^
+note: ...which requires caching mir of `Alpha::V3::{constant#0}` for CTFE...
+  --> $DIR/self-in-enum-definition.rs:5:10
+   |
+LL |     V3 = Self::V1 {} as u8 + 2,
+   |          ^^^^^^^^^^^^^^^^^^^^^
+note: ...which requires elaborating drops for `Alpha::V3::{constant#0}`...
+  --> $DIR/self-in-enum-definition.rs:5:10
+   |
+LL |     V3 = Self::V1 {} as u8 + 2,
+   |          ^^^^^^^^^^^^^^^^^^^^^
+note: ...which requires borrow-checking `Alpha::V3::{constant#0}`...
+  --> $DIR/self-in-enum-definition.rs:5:10
+   |
+LL |     V3 = Self::V1 {} as u8 + 2,
+   |          ^^^^^^^^^^^^^^^^^^^^^
+note: ...which requires processing MIR for `Alpha::V3::{constant#0}`...
+  --> $DIR/self-in-enum-definition.rs:5:10
+   |
+LL |     V3 = Self::V1 {} as u8 + 2,
+   |          ^^^^^^^^^^^^^^^^^^^^^
+note: ...which requires const checking `Alpha::V3::{constant#0}`...
+  --> $DIR/self-in-enum-definition.rs:5:10
+   |
+LL |     V3 = Self::V1 {} as u8 + 2,
+   |          ^^^^^^^^^^^^^^^^^^^^^
+note: ...which requires preparing `Alpha::V3::{constant#0}` for borrow checking...
+  --> $DIR/self-in-enum-definition.rs:5:10
+   |
+LL |     V3 = Self::V1 {} as u8 + 2,
+   |          ^^^^^^^^^^^^^^^^^^^^^
+note: ...which requires unsafety-checking `Alpha::V3::{constant#0}`...
+  --> $DIR/self-in-enum-definition.rs:5:10
+   |
+LL |     V3 = Self::V1 {} as u8 + 2,
+   |          ^^^^^^^^^^^^^^^^^^^^^
+note: ...which requires building MIR for `Alpha::V3::{constant#0}`...
+  --> $DIR/self-in-enum-definition.rs:5:10
+   |
 LL |     V3 = Self::V1 {} as u8 + 2,
    |          ^^^^^^^^^^^^^^^^^^^^^
    = note: ...which requires computing layout of `Alpha`...