1 files changed, 65 insertions, 0 deletions
diff --git a/tests/mir-opt/combine_transmutes.rs b/tests/mir-opt/combine_transmutes.rs
new file mode 100644
index 000000000..de9b9c35c
--- /dev/null
+++ b/tests/mir-opt/combine_transmutes.rs
@@ -0,0 +1,65 @@
+// unit-test: InstCombine
+// compile-flags: -C panic=abort
+
+#![crate_type = "lib"]
+#![feature(core_intrinsics)]
+#![feature(custom_mir)]
+
+use std::intrinsics::mir::*;
+use std::mem::{MaybeUninit, ManuallyDrop, transmute};
+
+// EMIT_MIR combine_transmutes.identity_transmutes.InstCombine.diff
+pub unsafe fn identity_transmutes() {
+    // These are nops and should be removed
+    let _a = transmute::<i32, i32>(1);
+    let _a = transmute::<Vec<i32>, Vec<i32>>(Vec::new());
+}
+
+#[custom_mir(dialect = "runtime", phase = "initial")]
+// EMIT_MIR combine_transmutes.integer_transmutes.InstCombine.diff
+pub unsafe fn integer_transmutes() {
+    mir! {
+        {
+            let A = CastTransmute::<i32, u32>(1); // Can be a cast
+            let B = CastTransmute::<i32, i64>(1); // UB
+            let C = CastTransmute::<u64, i64>(1); // Can be a cast
+            let D = CastTransmute::<u64, u32>(1); // UB
+            let E = CastTransmute::<isize, usize>(1); // Can be a cast
+            Return()
+        }
+    }
+}
+
+// EMIT_MIR combine_transmutes.adt_transmutes.InstCombine.diff
+pub unsafe fn adt_transmutes() {
+    let _a: u8 = transmute(EnumNoRepr::A);
+    let _a: i8 = transmute(EnumNoRepr::B);
+    let _a: usize = transmute(EnumReprIsize::A);
+    let _a: isize = transmute(EnumReprIsize::B);
+    let _a: u8 = transmute(std::cmp::Ordering::Less);
+    let _a: i8 = transmute(std::cmp::Ordering::Less);
+    let _a: u8 = transmute(Some(std::num::NonZeroU8::MAX));
+    let _a: i16 = transmute(std::num::Wrapping(0_i16));
+    let _a: u16 = transmute(std::num::Wrapping(0_i16));
+    let _a: u32 = transmute(Union32 { i32: 0 });
+    let _a: i32 = transmute(Union32 { u32: 0 });
+    let _a: ManuallyDrop<String> = transmute(MaybeUninit::<String>::uninit());
+}
+
+#[inline(always)]
+#[custom_mir(dialect = "runtime", phase = "initial")]
+const unsafe fn mir_transmute<T, U>(x: T) -> U {
+    mir!{
+        {
+            RET = CastTransmute(x);
+            Return()
+        }
+    }
+}
+
+pub enum EnumNoRepr { A, B, C }
+
+#[repr(isize)]
+pub enum EnumReprIsize { A, B, C }
+
+pub union Union32 { u32: u32, i32: i32 }