Merge pull request #776 from RalfJung/intrinsics

 implement unchecked_{add,sub,mul} intrinsics

Author: oli-obk

src/intrinsic.rs

@@ -272,7 +272,13 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 let b = this.read_immediate(args[1])?;
                 // check x % y != 0
                 if this.binary_op(mir::BinOp::Rem, a, b)?.0.to_bits(dest.layout.size)? != 0 {
-                    return err!(ValidationFailure(format!("exact_div: {:?} cannot be divided by {:?}", a, b)));
+                    // Check if `b` is -1, which is the "min_value / -1" case.
+                    let minus1 = Scalar::from_int(-1, dest.layout.size);
+                    return if b.to_scalar().unwrap() == minus1 {
+                        err!(Intrinsic(format!("exact_div: result of dividing MIN by -1 cannot be represented")))
+                    } else {
+                        err!(Intrinsic(format!("exact_div: {:?} cannot be divided by {:?} without remainder", *a, *b)))
+                    };
                 }
                 this.binop_ignore_overflow(mir::BinOp::Div, a, b, dest)?;
             },
@@ -459,6 +465,22 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                 )?;
             }
 
+            "unchecked_add" | "unchecked_sub" | "unchecked_mul" => {
+                let l = this.read_immediate(args[0])?;
+                let r = this.read_immediate(args[1])?;
+                let op = match intrinsic_name.get() {
+                    "unchecked_add" => mir::BinOp::Add,
+                    "unchecked_sub" => mir::BinOp::Sub,
+                    "unchecked_mul" => mir::BinOp::Mul,
+                    _ => bug!(),
+                };
+                let (res, overflowed) = this.binary_op(op, l, r)?;
+                if overflowed {
+                    return err!(Intrinsic(format!("Overflowing arithmetic in {}", intrinsic_name.get())));
+                }
+                this.write_scalar(res, dest)?;
+            }
+
             "uninit" => {
                 // Check fast path: we don't want to force an allocation in case the destination is a simple value,
                 // but we also do not want to create a new allocation with 0s and then copy that over.

tests/compile-fail/div-by-zero-3.rs

@@ -0,0 +1,11 @@
+#![feature(core_intrinsics)]
+
+use std::intrinsics::*;
+
+//error-pattern: Division by 0 in unchecked_rem
+
+fn main() {
+    unsafe {
+        let _n = unchecked_rem(3u32, 0);
+    }
+}

tests/compile-fail/exact_div1.rs

@@ -0,0 +1,5 @@
+#![feature(core_intrinsics)]
+fn main() {
+    // divison by 0
+    unsafe { std::intrinsics::exact_div(2, 0); } //~ ERROR divisor of zero
+}

tests/compile-fail/exact_div2.rs

@@ -0,0 +1,5 @@
+#![feature(core_intrinsics)]
+fn main() {
+    // divison with a remainder
+    unsafe { std::intrinsics::exact_div(2u16, 3); } //~ ERROR Scalar(0x0002) cannot be divided by Scalar(0x0003) without remainder
+}

tests/compile-fail/exact_div3.rs

@@ -0,0 +1,5 @@
+#![feature(core_intrinsics)]
+fn main() {
+    // signed divison with a remainder
+    unsafe { std::intrinsics::exact_div(-19i8, 2); } //~ ERROR Scalar(0xed) cannot be divided by Scalar(0x02) without remainder
+}

tests/compile-fail/exact_div4.rs

@@ -0,0 +1,5 @@
+#![feature(core_intrinsics)]
+fn main() {
+    // divison of min_value by -1
+    unsafe { std::intrinsics::exact_div(i64::min_value(), -1); } //~ ERROR result of dividing MIN by -1 cannot be represented
+}

tests/compile-fail/unchecked_add1.rs

@@ -0,0 +1,5 @@
+#![feature(core_intrinsics)]
+fn main() {
+    // MAX overflow
+    unsafe { std::intrinsics::unchecked_add(40000u16, 30000); } //~ ERROR Overflowing arithmetic in unchecked_add
+}

tests/compile-fail/unchecked_add2.rs

@@ -0,0 +1,5 @@
+#![feature(core_intrinsics)]
+fn main() {
+    // MIN overflow
+    unsafe { std::intrinsics::unchecked_add(-30000i16, -8000); } //~ ERROR Overflowing arithmetic in unchecked_add
+}

tests/compile-fail/unchecked_mul1.rs

@@ -0,0 +1,5 @@
+#![feature(core_intrinsics)]
+fn main() {
+    // MAX overflow
+    unsafe { std::intrinsics::unchecked_mul(300u16, 250u16); } //~ ERROR Overflowing arithmetic in unchecked_mul
+}

tests/compile-fail/unchecked_mul2.rs

@@ -0,0 +1,5 @@
+#![feature(core_intrinsics)]
+fn main() {
+    // MIN overflow
+    unsafe { std::intrinsics::unchecked_mul(1_000_000_000i32, -4); } //~ ERROR Overflowing arithmetic in unchecked_mul
+}