From 529b94ea6a3f0606d38e4bb32ec5eb692c3c0d71 Mon Sep 17 00:00:00 2001
From: Wesley Wiser <wwiser@gmail.com>
Date: Tue, 4 Jun 2019 21:51:30 -0400
Subject: [PATCH] [const-prop] Fix ICE when casting function pointers

This fixes an ICE when building libcore with `-Z mir-opt-level=3`.
---
 src/librustc_mir/transform/const_prop.rs    | 10 ++++-----
 src/test/mir-opt/const_prop/reify_fn_ptr.rs | 25 +++++++++++++++++++++
 2 files changed, 29 insertions(+), 6 deletions(-)
 create mode 100644 src/test/mir-opt/const_prop/reify_fn_ptr.rs

diff --git a/src/librustc_mir/transform/const_prop.rs b/src/librustc_mir/transform/const_prop.rs
index dbaa4e557c66..1d4d01e60aad 100644
--- a/src/librustc_mir/transform/const_prop.rs
+++ b/src/librustc_mir/transform/const_prop.rs
@@ -525,12 +525,10 @@ impl<'a, 'mir, 'tcx> ConstPropagator<'a, 'mir, 'tcx> {
         source_info: SourceInfo,
     ) {
         trace!("attepting to replace {:?} with {:?}", rval, value);
-        self.ecx.validate_operand(
-            value,
-            vec![],
-            None,
-            true,
-        ).expect("value should already be a valid const");
+        if let Err(e) = self.ecx.validate_operand(value, vec![], None, true) {
+            trace!("validation error, attempt failed: {:?}", e);
+            return;
+        }
 
         // FIXME> figure out what tho do when try_read_immediate fails
         let imm = self.use_ecx(source_info, |this| {
diff --git a/src/test/mir-opt/const_prop/reify_fn_ptr.rs b/src/test/mir-opt/const_prop/reify_fn_ptr.rs
new file mode 100644
index 000000000000..809eb19ade89
--- /dev/null
+++ b/src/test/mir-opt/const_prop/reify_fn_ptr.rs
@@ -0,0 +1,25 @@
+fn main() {
+    let _ = main as usize as *const fn();
+}
+
+// END RUST SOURCE
+// START rustc.main.ConstProp.before.mir
+//  bb0: {
+//      ...
+//      _3 = const main as fn() (Pointer(ReifyFnPointer));
+//      _2 = move _3 as usize (Misc);
+//      ...
+//      _1 = move _2 as *const fn() (Misc);
+//      ...
+//  }
+// END rustc.main.ConstProp.before.mir
+// START rustc.main.ConstProp.after.mir
+//  bb0: {
+//      ...
+//      _3 = const Scalar(AllocId(1).0x0) : fn();
+//      _2 = move _3 as usize (Misc);
+//      ...
+//      _1 = const Scalar(AllocId(1).0x0) : *const fn();
+//      ...
+//  }
+// END rustc.main.ConstProp.after.mir