Rollup merge of rust-lang#64063 - JohnTitor:fix-const-err, r=oli-obk

Fix const_err with `-(-0.0)`

Fixes rust-lang#64059

r? @oli-obk

src/librustc_mir/transform/const_prop.rs

@@ -405,13 +405,16 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
                 }
 
                 let arg = self.eval_operand(arg, source_info)?;
+                let oflo_check = self.tcx.sess.overflow_checks();
                 let val = self.use_ecx(source_info, |this| {
                     let prim = this.ecx.read_immediate(arg)?;
                     match op {
                         UnOp::Neg => {
-                            // Need to do overflow check here: For actual CTFE, MIR
-                            // generation emits code that does this before calling the op.
-                            if prim.to_bits()? == (1 << (prim.layout.size.bits() - 1)) {
+                            // We check overflow in debug mode already
+                            // so should only check in release mode.
+                            if !oflo_check
+                            && prim.layout.ty.is_signed()
+                            && prim.to_bits()? == (1 << (prim.layout.size.bits() - 1)) {
                                 throw_panic!(OverflowNeg)
                             }
                         }
@@ -485,7 +488,9 @@ impl<'mir, 'tcx> ConstPropagator<'mir, 'tcx> {
                         Scalar::from_bool(overflow).into(),
                     )
                 } else {
-                    if overflow {
+                    // We check overflow in debug mode already
+                    // so should only check in release mode.
+                    if !self.tcx.sess.overflow_checks() && overflow {
                         let err = err_panic!(Overflow(op)).into();
                         let _: Option<()> = self.use_ecx(source_info, |_| Err(err));
                         return None;

src/test/ui/consts/const-err2.rs

@@ -5,6 +5,7 @@
 
 #![feature(rustc_attrs)]
 #![allow(exceeding_bitshifts)]
+
 #![deny(const_err)]
 
 fn black_box<T>(_: T) {
@@ -21,7 +22,7 @@ fn main() {
     let d = 42u8 - (42u8 + 1);
     //~^ ERROR const_err
     let _e = [5u8][1];
-    //~^ ERROR const_err
+    //~^ ERROR index out of bounds
     black_box(a);
     black_box(b);
     black_box(c);

src/test/ui/consts/const-err2.stderr

@@ -1,35 +1,35 @@
 error: this expression will panic at runtime
-  --> $DIR/const-err2.rs:15:13
+  --> $DIR/const-err2.rs:16:13
    |
 LL |     let a = -std::i8::MIN;
    |             ^^^^^^^^^^^^^ attempt to negate with overflow
    |
 note: lint level defined here
-  --> $DIR/const-err2.rs:8:9
+  --> $DIR/const-err2.rs:9:9
    |
 LL | #![deny(const_err)]
    |         ^^^^^^^^^
 
 error: this expression will panic at runtime
-  --> $DIR/const-err2.rs:17:13
+  --> $DIR/const-err2.rs:18:13
    |
 LL |     let b = 200u8 + 200u8 + 200u8;
    |             ^^^^^^^^^^^^^ attempt to add with overflow
 
 error: this expression will panic at runtime
-  --> $DIR/const-err2.rs:19:13
+  --> $DIR/const-err2.rs:20:13
    |
 LL |     let c = 200u8 * 4;
    |             ^^^^^^^^^ attempt to multiply with overflow
 
 error: this expression will panic at runtime
-  --> $DIR/const-err2.rs:21:13
+  --> $DIR/const-err2.rs:22:13
    |
 LL |     let d = 42u8 - (42u8 + 1);
    |             ^^^^^^^^^^^^^^^^^ attempt to subtract with overflow
 
 error: index out of bounds: the len is 1 but the index is 1
-  --> $DIR/const-err2.rs:23:14
+  --> $DIR/const-err2.rs:24:14
    |
 LL |     let _e = [5u8][1];
    |              ^^^^^^^^

src/test/ui/consts/const-err3.rs

@@ -0,0 +1,30 @@
+// needed because negating int::MIN will behave differently between
+// optimized compilation and unoptimized compilation and thus would
+// lead to different lints being emitted
+// compile-flags: -C overflow-checks=on -O
+
+#![feature(rustc_attrs)]
+#![allow(exceeding_bitshifts)]
+
+#![deny(const_err)]
+
+fn black_box<T>(_: T) {
+    unimplemented!()
+}
+
+fn main() {
+    let a = -std::i8::MIN;
+    //~^ ERROR const_err
+    let b = 200u8 + 200u8 + 200u8;
+    //~^ ERROR const_err
+    let c = 200u8 * 4;
+    //~^ ERROR const_err
+    let d = 42u8 - (42u8 + 1);
+    //~^ ERROR const_err
+    let _e = [5u8][1];
+    //~^ ERROR const_err
+    black_box(a);
+    black_box(b);
+    black_box(c);
+    black_box(d);
+}

src/test/ui/consts/const-err3.stderr

@@ -0,0 +1,38 @@
+error: attempt to negate with overflow
+  --> $DIR/const-err3.rs:16:13
+   |
+LL |     let a = -std::i8::MIN;
+   |             ^^^^^^^^^^^^^
+   |
+note: lint level defined here
+  --> $DIR/const-err3.rs:9:9
+   |
+LL | #![deny(const_err)]
+   |         ^^^^^^^^^
+
+error: attempt to add with overflow
+  --> $DIR/const-err3.rs:18:13
+   |
+LL |     let b = 200u8 + 200u8 + 200u8;
+   |             ^^^^^^^^^^^^^
+
+error: attempt to multiply with overflow
+  --> $DIR/const-err3.rs:20:13
+   |
+LL |     let c = 200u8 * 4;
+   |             ^^^^^^^^^
+
+error: attempt to subtract with overflow
+  --> $DIR/const-err3.rs:22:13
+   |
+LL |     let d = 42u8 - (42u8 + 1);
+   |             ^^^^^^^^^^^^^^^^^
+
+error: index out of bounds: the len is 1 but the index is 1
+  --> $DIR/const-err3.rs:24:14
+   |
+LL |     let _e = [5u8][1];
+   |              ^^^^^^^^
+
+error: aborting due to 5 previous errors
+

src/test/ui/consts/const-eval/promoted_errors.rs

@@ -5,7 +5,7 @@
 fn main() {
     println!("{}", 0u32 - 1);
     let _x = 0u32 - 1;
-    //~^ ERROR this expression will panic at runtime [const_err]
+    //~^ ERROR const_err
     println!("{}", 1/(1-1));
     //~^ ERROR attempt to divide by zero [const_err]
     //~| ERROR reaching this expression at runtime will panic or abort [const_err]

src/test/ui/consts/const-eval/promoted_errors2.rs

@@ -0,0 +1,22 @@
+// compile-flags: -C overflow-checks=on -O
+
+#![deny(const_err)]
+
+fn main() {
+    println!("{}", 0u32 - 1);
+    //~^ ERROR attempt to subtract with overflow
+    let _x = 0u32 - 1;
+    //~^ ERROR attempt to subtract with overflow
+    println!("{}", 1/(1-1));
+    //~^ ERROR attempt to divide by zero [const_err]
+    //~| ERROR reaching this expression at runtime will panic or abort [const_err]
+    let _x = 1/(1-1);
+    //~^ ERROR const_err
+    //~| ERROR const_err
+    println!("{}", 1/(false as u32));
+    //~^ ERROR attempt to divide by zero [const_err]
+    //~| ERROR reaching this expression at runtime will panic or abort [const_err]
+    let _x = 1/(false as u32);
+    //~^ ERROR const_err
+    //~| ERROR const_err
+}

src/test/ui/consts/const-eval/promoted_errors2.stderr

@@ -0,0 +1,68 @@
+error: attempt to subtract with overflow
+  --> $DIR/promoted_errors2.rs:6:20
+   |
+LL |     println!("{}", 0u32 - 1);
+   |                    ^^^^^^^^
+   |
+note: lint level defined here
+  --> $DIR/promoted_errors2.rs:3:9
+   |
+LL | #![deny(const_err)]
+   |         ^^^^^^^^^
+
+error: attempt to subtract with overflow
+  --> $DIR/promoted_errors2.rs:8:14
+   |
+LL |     let _x = 0u32 - 1;
+   |              ^^^^^^^^
+
+error: attempt to divide by zero
+  --> $DIR/promoted_errors2.rs:10:20
+   |
+LL |     println!("{}", 1/(1-1));
+   |                    ^^^^^^^
+
+error: reaching this expression at runtime will panic or abort
+  --> $DIR/promoted_errors2.rs:10:20
+   |
+LL |     println!("{}", 1/(1-1));
+   |                    ^^^^^^^ attempt to divide by zero
+
+error: attempt to divide by zero
+  --> $DIR/promoted_errors2.rs:13:14
+   |
+LL |     let _x = 1/(1-1);
+   |              ^^^^^^^
+
+error: this expression will panic at runtime
+  --> $DIR/promoted_errors2.rs:13:14
+   |
+LL |     let _x = 1/(1-1);
+   |              ^^^^^^^ attempt to divide by zero
+
+error: attempt to divide by zero
+  --> $DIR/promoted_errors2.rs:16:20
+   |
+LL |     println!("{}", 1/(false as u32));
+   |                    ^^^^^^^^^^^^^^^^
+
+error: reaching this expression at runtime will panic or abort
+  --> $DIR/promoted_errors2.rs:16:20
+   |
+LL |     println!("{}", 1/(false as u32));
+   |                    ^^^^^^^^^^^^^^^^ attempt to divide by zero
+
+error: attempt to divide by zero
+  --> $DIR/promoted_errors2.rs:19:14
+   |
+LL |     let _x = 1/(false as u32);
+   |              ^^^^^^^^^^^^^^^^
+
+error: this expression will panic at runtime
+  --> $DIR/promoted_errors2.rs:19:14
+   |
+LL |     let _x = 1/(false as u32);
+   |              ^^^^^^^^^^^^^^^^ attempt to divide by zero
+
+error: aborting due to 10 previous errors
+

src/test/ui/consts/issue-64059-2.rs

@@ -0,0 +1,6 @@
+// compile-flags: -C overflow-checks=on -O
+// run-pass
+
+fn main() {
+    let _ = -(-0.0);
+}

src/test/ui/consts/issue-64059.rs

@@ -0,0 +1,5 @@
+// run-pass
+
+fn main() {
+    let _ = -(-0.0);
+}

src/test/ui/issues/issue-8460-const.rs

@@ -1,3 +1,5 @@
+// compile-flags: -O
+
 #![deny(const_err)]
 
 use std::{isize, i8, i16, i32, i64};