Rollup merge of #112168 - scottmcm:lower-div-rem-unchecked-to-mir, r=…

…oli-obk Lower `unchecked_div`/`_rem` to MIR's `BinOp::Div`/`Rem` As described in <https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/mir/enum.BinOp.html#variant.Div>, the ordinary `BinOp`s for these are already UB for division by zero ([or overflow](https://llvm.org/docs/LangRef.html#sdiv-instruction), [demo](https://rust.godbolt.org/z/71e7P7Exh)), as MIR building is responsible for inserting code to panic for those cases regardless of whether the overflow checks are enabled. So we can lower these in the same arm that lowers `wrapping_add` to MIR `BinOp::Add` and such, as all these cases turn into ordinary `Rvalue::BinaryOp`s.
rust-lang · Jun 2, 2023 · 5460f92 · 5460f92
2 parents dd09f4d + adb37d4
commit 5460f92
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diff --git a/compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs b/compiler/rustc_codegen_cranelift/src/intrinsics/mod.rs
@@ -475,9 +475,7 @@ fn codegen_regular_intrinsic_call<'tcx>(
         sym::unchecked_add
         | sym::unchecked_sub
         | sym::unchecked_mul
-        | sym::unchecked_div
         | sym::exact_div
-        | sym::unchecked_rem
         | sym::unchecked_shl
         | sym::unchecked_shr => {
             intrinsic_args!(fx, args => (x, y); intrinsic);
@@ -487,8 +485,7 @@ fn codegen_regular_intrinsic_call<'tcx>(
                 sym::unchecked_add => BinOp::Add,
                 sym::unchecked_sub => BinOp::Sub,
                 sym::unchecked_mul => BinOp::Mul,
-                sym::unchecked_div | sym::exact_div => BinOp::Div,
-                sym::unchecked_rem => BinOp::Rem,
+                sym::exact_div => BinOp::Div,
                 sym::unchecked_shl => BinOp::Shl,
                 sym::unchecked_shr => BinOp::Shr,
                 _ => unreachable!(),

diff --git a/compiler/rustc_codegen_ssa/src/mir/intrinsic.rs b/compiler/rustc_codegen_ssa/src/mir/intrinsic.rs
@@ -211,8 +211,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 args[1].val.unaligned_volatile_store(bx, dst);
                 return;
             }
-            | sym::unchecked_div
-            | sym::unchecked_rem
             | sym::unchecked_shl
             | sym::unchecked_shr
             | sym::unchecked_add
@@ -229,20 +227,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                                 bx.exactudiv(args[0].immediate(), args[1].immediate())
                             }
                         }
-                        sym::unchecked_div => {
-                            if signed {
-                                bx.sdiv(args[0].immediate(), args[1].immediate())
-                            } else {
-                                bx.udiv(args[0].immediate(), args[1].immediate())
-                            }
-                        }
-                        sym::unchecked_rem => {
-                            if signed {
-                                bx.srem(args[0].immediate(), args[1].immediate())
-                            } else {
-                                bx.urem(args[0].immediate(), args[1].immediate())
-                            }
-                        }
                         sym::unchecked_shl => bx.shl(args[0].immediate(), args[1].immediate()),
                         sym::unchecked_shr => {
                             if signed {

diff --git a/compiler/rustc_const_eval/src/interpret/intrinsics.rs b/compiler/rustc_const_eval/src/interpret/intrinsics.rs
@@ -238,9 +238,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             | sym::unchecked_shr
             | sym::unchecked_add
             | sym::unchecked_sub
-            | sym::unchecked_mul
-            | sym::unchecked_div
-            | sym::unchecked_rem => {
+            | sym::unchecked_mul => {
                 let l = self.read_immediate(&args[0])?;
                 let r = self.read_immediate(&args[1])?;
                 let bin_op = match intrinsic_name {
@@ -249,8 +247,6 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                     sym::unchecked_add => BinOp::Add,
                     sym::unchecked_sub => BinOp::Sub,
                     sym::unchecked_mul => BinOp::Mul,
-                    sym::unchecked_div => BinOp::Div,
-                    sym::unchecked_rem => BinOp::Rem,
                     _ => bug!(),
                 };
                 let (val, overflowed, _ty) = self.overflowing_binary_op(bin_op, &l, &r)?;

diff --git a/compiler/rustc_middle/src/mir/syntax.rs b/compiler/rustc_middle/src/mir/syntax.rs
@@ -1273,13 +1273,18 @@ pub enum BinOp {
     Mul,
     /// The `/` operator (division)
     ///
-    /// Division by zero is UB, because the compiler should have inserted checks
-    /// prior to this.
+    /// For integer types, division by zero is UB, as is `MIN / -1` for signed.
+    /// The compiler should have inserted checks prior to this.
+    ///
+    /// Floating-point division by zero is safe, and does not need guards.
     Div,
     /// The `%` operator (modulus)
     ///
-    /// Using zero as the modulus (second operand) is UB, because the compiler
-    /// should have inserted checks prior to this.
+    /// For integer types, using zero as the modulus (second operand) is UB,
+    /// as is `MIN % -1` for signed.
+    /// The compiler should have inserted checks prior to this.
+    ///
+    /// Floating-point remainder by zero is safe, and does not need guards.
     Rem,
     /// The `^` operator (bitwise xor)
     BitXor,

diff --git a/compiler/rustc_mir_transform/src/lower_intrinsics.rs b/compiler/rustc_mir_transform/src/lower_intrinsics.rs
@@ -82,30 +82,35 @@ impl<'tcx> MirPass<'tcx> for LowerIntrinsics {
                         drop(args);
                         terminator.kind = TerminatorKind::Goto { target };
                     }
-                    sym::wrapping_add | sym::wrapping_sub | sym::wrapping_mul => {
-                        if let Some(target) = *target {
-                            let lhs;
-                            let rhs;
-                            {
-                                let mut args = args.drain(..);
-                                lhs = args.next().unwrap();
-                                rhs = args.next().unwrap();
-                            }
-                            let bin_op = match intrinsic_name {
-                                sym::wrapping_add => BinOp::Add,
-                                sym::wrapping_sub => BinOp::Sub,
-                                sym::wrapping_mul => BinOp::Mul,
-                                _ => bug!("unexpected intrinsic"),
-                            };
-                            block.statements.push(Statement {
-                                source_info: terminator.source_info,
-                                kind: StatementKind::Assign(Box::new((
-                                    *destination,
-                                    Rvalue::BinaryOp(bin_op, Box::new((lhs, rhs))),
-                                ))),
-                            });
-                            terminator.kind = TerminatorKind::Goto { target };
+                    sym::wrapping_add
+                    | sym::wrapping_sub
+                    | sym::wrapping_mul
+                    | sym::unchecked_div
+                    | sym::unchecked_rem => {
+                        let target = target.unwrap();
+                        let lhs;
+                        let rhs;
+                        {
+                            let mut args = args.drain(..);
+                            lhs = args.next().unwrap();
+                            rhs = args.next().unwrap();
                         }
+                        let bin_op = match intrinsic_name {
+                            sym::wrapping_add => BinOp::Add,
+                            sym::wrapping_sub => BinOp::Sub,
+                            sym::wrapping_mul => BinOp::Mul,
+                            sym::unchecked_div => BinOp::Div,
+                            sym::unchecked_rem => BinOp::Rem,
+                            _ => bug!("unexpected intrinsic"),
+                        };
+                        block.statements.push(Statement {
+                            source_info: terminator.source_info,
+                            kind: StatementKind::Assign(Box::new((
+                                *destination,
+                                Rvalue::BinaryOp(bin_op, Box::new((lhs, rhs))),
+                            ))),
+                        });
+                        terminator.kind = TerminatorKind::Goto { target };
                     }
                     sym::add_with_overflow | sym::sub_with_overflow | sym::mul_with_overflow => {
                         if let Some(target) = *target {

diff --git a/tests/mir-opt/lower_intrinsics.align_of.LowerIntrinsics.diff b/tests/mir-opt/lower_intrinsics.align_of.LowerIntrinsics.diff
@@ -7,7 +7,7 @@
       bb0: {
 -         _0 = std::intrinsics::min_align_of::<T>() -> [return: bb1, unwind unreachable]; // scope 0 at $DIR/lower_intrinsics.rs:+1:5: +1:42
 -                                          // mir::Constant
--                                          // + span: $DIR/lower_intrinsics.rs:21:5: 21:40
+-                                          // + span: $DIR/lower_intrinsics.rs:27:5: 27:40
 -                                          // + literal: Const { ty: extern "rust-intrinsic" fn() -> usize {std::intrinsics::min_align_of::<T>}, val: Value(<ZST>) }
 +         _0 = AlignOf(T);                 // scope 0 at $DIR/lower_intrinsics.rs:+1:5: +1:42
 +         goto -> bb1;                     // scope 0 at $DIR/lower_intrinsics.rs:+1:5: +1:42

diff --git a/tests/mir-opt/lower_intrinsics.assume.LowerIntrinsics.diff b/tests/mir-opt/lower_intrinsics.assume.LowerIntrinsics.diff
@@ -11,7 +11,7 @@
           StorageLive(_1);                 // scope 1 at $DIR/lower_intrinsics.rs:+2:9: +2:38
 -         _1 = std::intrinsics::assume(const true) -> [return: bb1, unwind unreachable]; // scope 1 at $DIR/lower_intrinsics.rs:+2:9: +2:38
 -                                          // mir::Constant
--                                          // + span: $DIR/lower_intrinsics.rs:106:9: 106:32
+-                                          // + span: $DIR/lower_intrinsics.rs:112:9: 112:32
 -                                          // + literal: Const { ty: unsafe extern "rust-intrinsic" fn(bool) {std::intrinsics::assume}, val: Value(<ZST>) }
 +         assume(const true);              // scope 1 at $DIR/lower_intrinsics.rs:+2:9: +2:38
 +         goto -> bb1;                     // scope 1 at $DIR/lower_intrinsics.rs:+2:9: +2:38

diff --git a/tests/mir-opt/lower_intrinsics.discriminant.LowerIntrinsics.diff b/tests/mir-opt/lower_intrinsics.discriminant.LowerIntrinsics.diff
@@ -31,7 +31,7 @@
           _3 = &(*_4);                     // scope 0 at $DIR/lower_intrinsics.rs:+1:42: +1:44
 -         _2 = discriminant_value::<T>(move _3) -> [return: bb1, unwind unreachable]; // scope 0 at $DIR/lower_intrinsics.rs:+1:5: +1:45
 -                                          // mir::Constant
--                                          // + span: $DIR/lower_intrinsics.rs:82:5: 82:41
+-                                          // + span: $DIR/lower_intrinsics.rs:88:5: 88:41
 -                                          // + literal: Const { ty: for<'a> extern "rust-intrinsic" fn(&'a T) -> <T as DiscriminantKind>::Discriminant {discriminant_value::<T>}, val: Value(<ZST>) }
 +         _2 = discriminant((*_3));        // scope 0 at $DIR/lower_intrinsics.rs:+1:5: +1:45
 +         goto -> bb1;                     // scope 0 at $DIR/lower_intrinsics.rs:+1:5: +1:45
@@ -46,13 +46,13 @@
           StorageLive(_7);                 // scope 0 at $DIR/lower_intrinsics.rs:+2:42: +2:44
           _19 = const _;                   // scope 0 at $DIR/lower_intrinsics.rs:+2:42: +2:44
                                            // mir::Constant
-                                           // + span: $DIR/lower_intrinsics.rs:83:42: 83:44
+                                           // + span: $DIR/lower_intrinsics.rs:89:42: 89:44
                                            // + literal: Const { ty: &i32, val: Unevaluated(discriminant, [T], Some(promoted[2])) }
           _7 = &(*_19);                    // scope 0 at $DIR/lower_intrinsics.rs:+2:42: +2:44
           _6 = &(*_7);                     // scope 0 at $DIR/lower_intrinsics.rs:+2:42: +2:44
 -         _5 = discriminant_value::<i32>(move _6) -> [return: bb2, unwind unreachable]; // scope 0 at $DIR/lower_intrinsics.rs:+2:5: +2:45
 -                                          // mir::Constant
--                                          // + span: $DIR/lower_intrinsics.rs:83:5: 83:41
+-                                          // + span: $DIR/lower_intrinsics.rs:89:5: 89:41
 -                                          // + literal: Const { ty: for<'a> extern "rust-intrinsic" fn(&'a i32) -> <i32 as DiscriminantKind>::Discriminant {discriminant_value::<i32>}, val: Value(<ZST>) }
 +         _5 = discriminant((*_6));        // scope 0 at $DIR/lower_intrinsics.rs:+2:5: +2:45
 +         goto -> bb2;                     // scope 0 at $DIR/lower_intrinsics.rs:+2:5: +2:45
@@ -67,13 +67,13 @@
           StorageLive(_11);                // scope 0 at $DIR/lower_intrinsics.rs:+3:42: +3:45
           _18 = const _;                   // scope 0 at $DIR/lower_intrinsics.rs:+3:42: +3:45
                                            // mir::Constant
-                                           // + span: $DIR/lower_intrinsics.rs:84:42: 84:45
+                                           // + span: $DIR/lower_intrinsics.rs:90:42: 90:45
                                            // + literal: Const { ty: &(), val: Unevaluated(discriminant, [T], Some(promoted[1])) }
           _11 = &(*_18);                   // scope 0 at $DIR/lower_intrinsics.rs:+3:42: +3:45
           _10 = &(*_11);                   // scope 0 at $DIR/lower_intrinsics.rs:+3:42: +3:45
 -         _9 = discriminant_value::<()>(move _10) -> [return: bb3, unwind unreachable]; // scope 0 at $DIR/lower_intrinsics.rs:+3:5: +3:46
 -                                          // mir::Constant
--                                          // + span: $DIR/lower_intrinsics.rs:84:5: 84:41
+-                                          // + span: $DIR/lower_intrinsics.rs:90:5: 90:41
 -                                          // + literal: Const { ty: for<'a> extern "rust-intrinsic" fn(&'a ()) -> <() as DiscriminantKind>::Discriminant {discriminant_value::<()>}, val: Value(<ZST>) }
 +         _9 = discriminant((*_10));       // scope 0 at $DIR/lower_intrinsics.rs:+3:5: +3:46
 +         goto -> bb3;                     // scope 0 at $DIR/lower_intrinsics.rs:+3:5: +3:46
@@ -88,13 +88,13 @@
           StorageLive(_15);                // scope 0 at $DIR/lower_intrinsics.rs:+4:42: +4:47
           _17 = const _;                   // scope 0 at $DIR/lower_intrinsics.rs:+4:42: +4:47
                                            // mir::Constant
-                                           // + span: $DIR/lower_intrinsics.rs:85:42: 85:47
+                                           // + span: $DIR/lower_intrinsics.rs:91:42: 91:47
                                            // + literal: Const { ty: &E, val: Unevaluated(discriminant, [T], Some(promoted[0])) }
           _15 = &(*_17);                   // scope 0 at $DIR/lower_intrinsics.rs:+4:42: +4:47
           _14 = &(*_15);                   // scope 0 at $DIR/lower_intrinsics.rs:+4:42: +4:47
 -         _13 = discriminant_value::<E>(move _14) -> [return: bb4, unwind unreachable]; // scope 0 at $DIR/lower_intrinsics.rs:+4:5: +4:48
 -                                          // mir::Constant
--                                          // + span: $DIR/lower_intrinsics.rs:85:5: 85:41
+-                                          // + span: $DIR/lower_intrinsics.rs:91:5: 91:41
 -                                          // + literal: Const { ty: for<'a> extern "rust-intrinsic" fn(&'a E) -> <E as DiscriminantKind>::Discriminant {discriminant_value::<E>}, val: Value(<ZST>) }
 +         _13 = discriminant((*_14));      // scope 0 at $DIR/lower_intrinsics.rs:+4:5: +4:48
 +         goto -> bb4;                     // scope 0 at $DIR/lower_intrinsics.rs:+4:5: +4:48

diff --git a/tests/mir-opt/lower_intrinsics.f_copy_nonoverlapping.LowerIntrinsics.diff b/tests/mir-opt/lower_intrinsics.f_copy_nonoverlapping.LowerIntrinsics.diff
@@ -49,7 +49,7 @@
           StorageDead(_9);                 // scope 3 at $DIR/lower_intrinsics.rs:+4:90: +4:91
 -         _3 = copy_nonoverlapping::<i32>(move _4, move _8, const 0_usize) -> [return: bb1, unwind unreachable]; // scope 3 at $DIR/lower_intrinsics.rs:+4:9: +4:95
 -                                          // mir::Constant
--                                          // + span: $DIR/lower_intrinsics.rs:99:9: 99:28
+-                                          // + span: $DIR/lower_intrinsics.rs:105:9: 105:28
 -                                          // + literal: Const { ty: unsafe extern "rust-intrinsic" fn(*const i32, *mut i32, usize) {copy_nonoverlapping::<i32>}, val: Value(<ZST>) }
 +         copy_nonoverlapping(dst = move _8, src = move _4, count = const 0_usize); // scope 3 at $DIR/lower_intrinsics.rs:+4:9: +4:95
 +         goto -> bb1;                     // scope 3 at $DIR/lower_intrinsics.rs:+4:9: +4:95

diff --git a/tests/mir-opt/lower_intrinsics.forget.LowerIntrinsics.diff b/tests/mir-opt/lower_intrinsics.forget.LowerIntrinsics.diff
@@ -11,7 +11,7 @@
           _2 = move _1;                    // scope 0 at $DIR/lower_intrinsics.rs:+1:30: +1:31
 -         _0 = std::intrinsics::forget::<T>(move _2) -> [return: bb1, unwind unreachable]; // scope 0 at $DIR/lower_intrinsics.rs:+1:5: +1:32
 -                                          // mir::Constant
--                                          // + span: $DIR/lower_intrinsics.rs:26:5: 26:29
+-                                          // + span: $DIR/lower_intrinsics.rs:32:5: 32:29
 -                                          // + literal: Const { ty: extern "rust-intrinsic" fn(T) {std::intrinsics::forget::<T>}, val: Value(<ZST>) }
 +         _0 = const ();                   // scope 0 at $DIR/lower_intrinsics.rs:+1:5: +1:32
 +         goto -> bb1;                     // scope 0 at $DIR/lower_intrinsics.rs:+1:5: +1:32

diff --git a/tests/mir-opt/lower_intrinsics.non_const.LowerIntrinsics.diff b/tests/mir-opt/lower_intrinsics.non_const.LowerIntrinsics.diff
@@ -13,7 +13,7 @@
           StorageLive(_1);                 // scope 0 at $DIR/lower_intrinsics.rs:+2:9: +2:18
           _1 = std::intrinsics::size_of::<T>; // scope 0 at $DIR/lower_intrinsics.rs:+2:21: +2:51
                                            // mir::Constant
-                                           // + span: $DIR/lower_intrinsics.rs:37:21: 37:51
+                                           // + span: $DIR/lower_intrinsics.rs:43:21: 43:51
                                            // + literal: Const { ty: extern "rust-intrinsic" fn() -> usize {std::intrinsics::size_of::<T>}, val: Value(<ZST>) }
           StorageLive(_2);                 // scope 1 at $DIR/lower_intrinsics.rs:+3:5: +3:14
           _2 = _1;                         // scope 1 at $DIR/lower_intrinsics.rs:+3:5: +3:14

diff --git a/tests/mir-opt/lower_intrinsics.option_payload.LowerIntrinsics.diff b/tests/mir-opt/lower_intrinsics.option_payload.LowerIntrinsics.diff
@@ -24,7 +24,7 @@
           _4 = &raw const (*_1);           // scope 1 at $DIR/lower_intrinsics.rs:+2:55: +2:56
 -         _3 = option_payload_ptr::<usize>(move _4) -> [return: bb1, unwind unreachable]; // scope 1 at $DIR/lower_intrinsics.rs:+2:18: +2:57
 -                                          // mir::Constant
--                                          // + span: $DIR/lower_intrinsics.rs:137:18: 137:54
+-                                          // + span: $DIR/lower_intrinsics.rs:143:18: 143:54
 -                                          // + literal: Const { ty: unsafe extern "rust-intrinsic" fn(*const Option<usize>) -> *const usize {option_payload_ptr::<usize>}, val: Value(<ZST>) }
 +         _3 = &raw const (((*_4) as Some).0: usize); // scope 1 at $DIR/lower_intrinsics.rs:+2:18: +2:57
 +         goto -> bb1;                     // scope 1 at $DIR/lower_intrinsics.rs:+2:18: +2:57
@@ -37,7 +37,7 @@
           _6 = &raw const (*_2);           // scope 2 at $DIR/lower_intrinsics.rs:+3:55: +3:56
 -         _5 = option_payload_ptr::<String>(move _6) -> [return: bb2, unwind unreachable]; // scope 2 at $DIR/lower_intrinsics.rs:+3:18: +3:57
 -                                          // mir::Constant
--                                          // + span: $DIR/lower_intrinsics.rs:138:18: 138:54
+-                                          // + span: $DIR/lower_intrinsics.rs:144:18: 144:54
 -                                          // + literal: Const { ty: unsafe extern "rust-intrinsic" fn(*const Option<String>) -> *const String {option_payload_ptr::<String>}, val: Value(<ZST>) }
 +         _5 = &raw const (((*_6) as Some).0: std::string::String); // scope 2 at $DIR/lower_intrinsics.rs:+3:18: +3:57
 +         goto -> bb2;                     // scope 2 at $DIR/lower_intrinsics.rs:+3:18: +3:57

diff --git a/tests/mir-opt/lower_intrinsics.ptr_offset.LowerIntrinsics.diff b/tests/mir-opt/lower_intrinsics.ptr_offset.LowerIntrinsics.diff
@@ -15,7 +15,7 @@
           _4 = _2;                         // scope 0 at $DIR/lower_intrinsics.rs:+1:33: +1:34
 -         _0 = offset::<*const i32, isize>(move _3, move _4) -> [return: bb1, unwind unreachable]; // scope 0 at $DIR/lower_intrinsics.rs:+1:5: +1:35
 -                                          // mir::Constant
--                                          // + span: $DIR/lower_intrinsics.rs:144:5: 144:29
+-                                          // + span: $DIR/lower_intrinsics.rs:150:5: 150:29
 -                                          // + literal: Const { ty: unsafe extern "rust-intrinsic" fn(*const i32, isize) -> *const i32 {offset::<*const i32, isize>}, val: Value(<ZST>) }
 +         _0 = Offset(move _3, move _4);   // scope 0 at $DIR/lower_intrinsics.rs:+1:5: +1:35
 +         goto -> bb1;                     // scope 0 at $DIR/lower_intrinsics.rs:+1:5: +1:35