From fc901244890cf2c0218027189d9d2311026dabbd Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Sun, 16 Jun 2019 10:51:08 +0200
Subject: [PATCH] test exact_div UB detection

---
 src/intrinsic.rs                 | 8 +++++++-
 tests/compile-fail/exact_div1.rs | 5 +++++
 tests/compile-fail/exact_div2.rs | 5 +++++
 tests/compile-fail/exact_div3.rs | 5 +++++
 tests/compile-fail/exact_div4.rs | 5 +++++
 5 files changed, 27 insertions(+), 1 deletion(-)
 create mode 100644 tests/compile-fail/exact_div1.rs
 create mode 100644 tests/compile-fail/exact_div2.rs
 create mode 100644 tests/compile-fail/exact_div3.rs
 create mode 100644 tests/compile-fail/exact_div4.rs

diff --git a/src/intrinsic.rs b/src/intrinsic.rs
index cd89055b467..cf2afe0a811 100644
--- a/src/intrinsic.rs
+++ b/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)?;
             },
diff --git a/tests/compile-fail/exact_div1.rs b/tests/compile-fail/exact_div1.rs
new file mode 100644
index 00000000000..171bedeadc6
--- /dev/null
+++ b/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
+}
diff --git a/tests/compile-fail/exact_div2.rs b/tests/compile-fail/exact_div2.rs
new file mode 100644
index 00000000000..22bcf027dd0
--- /dev/null
+++ b/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
+}
diff --git a/tests/compile-fail/exact_div3.rs b/tests/compile-fail/exact_div3.rs
new file mode 100644
index 00000000000..2db62e0092d
--- /dev/null
+++ b/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
+}
diff --git a/tests/compile-fail/exact_div4.rs b/tests/compile-fail/exact_div4.rs
new file mode 100644
index 00000000000..736d4f2516d
--- /dev/null
+++ b/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
+}