skip double negation in const eval

Author: oli-obk

src/librustc_const_eval/eval.rs

@@ -562,44 +562,51 @@ pub fn eval_const_expr_partial<'tcx>(tcx: &TyCtxt<'tcx>,
     let result = match e.node {
       hir::ExprUnary(hir::UnNeg, ref inner) => {
         // unary neg literals already got their sign during creation
-        if let hir::ExprLit(ref lit) = inner.node {
-            use syntax::ast::*;
-            use syntax::ast::LitIntType::*;
-            const I8_OVERFLOW: u64 = ::std::i8::MAX as u64 + 1;
-            const I16_OVERFLOW: u64 = ::std::i16::MAX as u64 + 1;
-            const I32_OVERFLOW: u64 = ::std::i32::MAX as u64 + 1;
-            const I64_OVERFLOW: u64 = ::std::i64::MAX as u64 + 1;
-            match (&lit.node, ety.map(|t| &t.sty)) {
-                (&LitKind::Int(I8_OVERFLOW, Unsuffixed), Some(&ty::TyInt(IntTy::I8))) |
-                (&LitKind::Int(I8_OVERFLOW, Signed(IntTy::I8)), _) => {
-                    return Ok(Integral(I8(::std::i8::MIN)))
-                },
-                (&LitKind::Int(I16_OVERFLOW, Unsuffixed), Some(&ty::TyInt(IntTy::I16))) |
-                (&LitKind::Int(I16_OVERFLOW, Signed(IntTy::I16)), _) => {
-                    return Ok(Integral(I16(::std::i16::MIN)))
-                },
-                (&LitKind::Int(I32_OVERFLOW, Unsuffixed), Some(&ty::TyInt(IntTy::I32))) |
-                (&LitKind::Int(I32_OVERFLOW, Signed(IntTy::I32)), _) => {
-                    return Ok(Integral(I32(::std::i32::MIN)))
-                },
-                (&LitKind::Int(I64_OVERFLOW, Unsuffixed), Some(&ty::TyInt(IntTy::I64))) |
-                (&LitKind::Int(I64_OVERFLOW, Signed(IntTy::I64)), _) => {
-                    return Ok(Integral(I64(::std::i64::MIN)))
-                },
-                (&LitKind::Int(n, Unsuffixed), Some(&ty::TyInt(IntTy::Is))) |
-                (&LitKind::Int(n, Signed(IntTy::Is)), _) => {
-                    match tcx.sess.target.int_type {
-                        IntTy::I32 => if n == I32_OVERFLOW {
-                            return Ok(Integral(Isize(Is32(::std::i32::MIN))));
-                        },
-                        IntTy::I64 => if n == I64_OVERFLOW {
-                            return Ok(Integral(Isize(Is64(::std::i64::MIN))));
-                        },
-                        _ => bug!(),
-                    }
-                },
-                _ => {},
-            }
+        match inner.node {
+            hir::ExprLit(ref lit) => {
+                use syntax::ast::*;
+                use syntax::ast::LitIntType::*;
+                const I8_OVERFLOW: u64 = ::std::i8::MAX as u64 + 1;
+                const I16_OVERFLOW: u64 = ::std::i16::MAX as u64 + 1;
+                const I32_OVERFLOW: u64 = ::std::i32::MAX as u64 + 1;
+                const I64_OVERFLOW: u64 = ::std::i64::MAX as u64 + 1;
+                match (&lit.node, ety.map(|t| &t.sty)) {
+                    (&LitKind::Int(I8_OVERFLOW, Unsuffixed), Some(&ty::TyInt(IntTy::I8))) |
+                    (&LitKind::Int(I8_OVERFLOW, Signed(IntTy::I8)), _) => {
+                        return Ok(Integral(I8(::std::i8::MIN)))
+                    },
+                    (&LitKind::Int(I16_OVERFLOW, Unsuffixed), Some(&ty::TyInt(IntTy::I16))) |
+                    (&LitKind::Int(I16_OVERFLOW, Signed(IntTy::I16)), _) => {
+                        return Ok(Integral(I16(::std::i16::MIN)))
+                    },
+                    (&LitKind::Int(I32_OVERFLOW, Unsuffixed), Some(&ty::TyInt(IntTy::I32))) |
+                    (&LitKind::Int(I32_OVERFLOW, Signed(IntTy::I32)), _) => {
+                        return Ok(Integral(I32(::std::i32::MIN)))
+                    },
+                    (&LitKind::Int(I64_OVERFLOW, Unsuffixed), Some(&ty::TyInt(IntTy::I64))) |
+                    (&LitKind::Int(I64_OVERFLOW, Signed(IntTy::I64)), _) => {
+                        return Ok(Integral(I64(::std::i64::MIN)))
+                    },
+                    (&LitKind::Int(n, Unsuffixed), Some(&ty::TyInt(IntTy::Is))) |
+                    (&LitKind::Int(n, Signed(IntTy::Is)), _) => {
+                        match tcx.sess.target.int_type {
+                            IntTy::I32 => if n == I32_OVERFLOW {
+                                return Ok(Integral(Isize(Is32(::std::i32::MIN))));
+                            },
+                            IntTy::I64 => if n == I64_OVERFLOW {
+                                return Ok(Integral(Isize(Is64(::std::i64::MIN))));
+                            },
+                            _ => bug!(),
+                        }
+                    },
+                    _ => {},
+                }
+            },
+            hir::ExprUnary(hir::UnNeg, ref inner) => {
+                // skip `--$expr`
+                return eval_const_expr_partial(tcx, inner, ty_hint, fn_args);
+            },
+            _ => {},
         }
         match eval_const_expr_partial(tcx, &inner, ty_hint, fn_args)? {
           Float(f) => Float(-f),

src/test/compile-fail/lint-type-overflow2.rs

@@ -15,7 +15,6 @@
 #[allow(unused_variables)]
 fn main() {
     let x2: i8 = --128; //~ error: literal out of range for i8
-    //~^ error: attempted to negate with overflow
 
     let x = -3.40282348e+38_f32; //~ error: literal out of range for f32
     let x =  3.40282348e+38_f32; //~ error: literal out of range for f32