Support pretty printing of invalid constants

Make it possible to pretty print invalid constants by introducing a
fallible variant of `destructure_const` and falling back to debug
formatting when it fails.

2 files changed, 72 insertions, 0 deletions

diff --git a/src/test/mir-opt/const_prop/invalid_constant.main.ConstProp.diff b/src/test/mir-opt/const_prop/invalid_constant.main.ConstProp.diff
new file mode 100644
index 00000000000..ee6c3b5f36f
--- /dev/null
+++ b/src/test/mir-opt/const_prop/invalid_constant.main.ConstProp.diff
@@ -0,0 +1,55 @@
+- // MIR for `main` before ConstProp
++ // MIR for `main` after ConstProp
+  
+  fn main() -> () {
+      let mut _0: ();                      // return place in scope 0 at $DIR/invalid_constant.rs:15:11: 15:11
+      let _1: std::option::Option<()>;     // in scope 0 at $DIR/invalid_constant.rs:16:5: 16:12
+      let mut _2: std::option::Option<std::option::Option<()>>; // in scope 0 at $DIR/invalid_constant.rs:16:7: 16:11
+      scope 1 (inlined f) {                // at $DIR/invalid_constant.rs:16:5: 16:12
+          debug x => _2;                   // in scope 1 at $DIR/invalid_constant.rs:16:5: 16:12
+          let mut _3: isize;               // in scope 1 at $DIR/invalid_constant.rs:16:5: 16:12
+          let _4: std::option::Option<()>; // in scope 1 at $DIR/invalid_constant.rs:16:5: 16:12
+          scope 2 {
+              debug y => _4;               // in scope 2 at $DIR/invalid_constant.rs:16:5: 16:12
+          }
+      }
+  
+      bb0: {
+          discriminant(_2) = 0;            // scope 0 at $DIR/invalid_constant.rs:16:7: 16:11
+-         _3 = discriminant(_2);           // scope 1 at $DIR/invalid_constant.rs:16:5: 16:12
+-         switchInt(move _3) -> [0_isize: bb3, otherwise: bb2]; // scope 1 at $DIR/invalid_constant.rs:16:5: 16:12
++         _3 = const 0_isize;              // scope 1 at $DIR/invalid_constant.rs:16:5: 16:12
++         switchInt(const 0_isize) -> [0_isize: bb3, otherwise: bb2]; // scope 1 at $DIR/invalid_constant.rs:16:5: 16:12
+      }
+  
+      bb1: {
+          nop;                             // scope 0 at $DIR/invalid_constant.rs:15:11: 17:2
+          return;                          // scope 0 at $DIR/invalid_constant.rs:17:2: 17:2
+      }
+  
+      bb2: {
+-         _4 = ((_2 as Some).0: std::option::Option<()>); // scope 1 at $DIR/invalid_constant.rs:16:5: 16:12
+-         _1 = _4;                         // scope 2 at $DIR/invalid_constant.rs:16:5: 16:12
++         _4 = const Scalar(0x02): Option::<()>; // scope 1 at $DIR/invalid_constant.rs:16:5: 16:12
++                                          // ty::Const
++                                          // + ty: std::option::Option<()>
++                                          // + val: Value(Scalar(0x02))
++                                          // mir::Constant
++                                          // + span: $DIR/invalid_constant.rs:16:5: 16:12
++                                          // + literal: Const { ty: std::option::Option<()>, val: Value(Scalar(0x02)) }
++         _1 = const Scalar(0x02): Option::<()>; // scope 2 at $DIR/invalid_constant.rs:16:5: 16:12
++                                          // ty::Const
++                                          // + ty: std::option::Option<()>
++                                          // + val: Value(Scalar(0x02))
++                                          // mir::Constant
++                                          // + span: $DIR/invalid_constant.rs:16:5: 16:12
++                                          // + literal: Const { ty: std::option::Option<()>, val: Value(Scalar(0x02)) }
+          goto -> bb1;                     // scope 0 at $DIR/invalid_constant.rs:10:20: 10:21
+      }
+  
+      bb3: {
+          discriminant(_1) = 0;            // scope 1 at $DIR/invalid_constant.rs:16:5: 16:12
+          goto -> bb1;                     // scope 0 at $DIR/invalid_constant.rs:9:17: 9:21
+      }
+  }
+  
diff --git a/src/test/mir-opt/const_prop/invalid_constant.rs b/src/test/mir-opt/const_prop/invalid_constant.rs
new file mode 100644
index 00000000000..1eb6f37df59
--- /dev/null
+++ b/src/test/mir-opt/const_prop/invalid_constant.rs
@@ -0,0 +1,17 @@
+// Verify that we can pretty print invalid constant introduced
+// by constant propagation. Regression test for issue #93688.
+//
+// compile-flags: -Copt-level=0 -Zinline-mir
+
+#[inline(always)]
+pub fn f(x: Option<Option<()>>) -> Option<()> {
+    match x {
+        None => None,
+        Some(y) => y,
+    }
+}
+
+// EMIT_MIR invalid_constant.main.ConstProp.diff
+fn main() {
+    f(None);
+}