[mir-opt] Allow debuginfo to be generated for a constant or a Place

Prior to this commit, debuginfo was always generated by mapping a name
to a Place. This has the side-effect that `SimplifyLocals` cannot remove
locals that are only used for debuginfo because their other uses have
been const-propagated.

To allow these locals to be removed, we now allow debuginfo to point to
a constant value. The `ConstProp` pass detects when debuginfo points to
a local with a known constant value and replaces it with the value. This
allows the later `SimplifyLocals` pass to remove the local.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/test/incremental/hashes/let_expressions.rs b/src/test/incremental/hashes/let_expressions.rs
index 918e72582d6..2c37b2e78ff 100644
--- a/src/test/incremental/hashes/let_expressions.rs
+++ b/src/test/incremental/hashes/let_expressions.rs
@@ -86,7 +86,7 @@ pub fn change_mutability_of_slot() {
 
 #[cfg(not(cfail1))]
 #[rustc_clean(cfg="cfail2",
-    except="hir_owner_nodes,typeck,optimized_mir")]
+    except="hir_owner_nodes,typeck")]
 #[rustc_clean(cfg="cfail3")]
 pub fn change_mutability_of_slot() {
     let _x: u64 = 0;
@@ -166,7 +166,7 @@ pub fn change_mutability_of_binding_in_pattern() {
 
 #[cfg(not(cfail1))]
 #[rustc_clean(cfg="cfail2",
-    except="hir_owner_nodes,typeck,optimized_mir")]
+    except="hir_owner_nodes,typeck")]
 #[rustc_clean(cfg="cfail3")]
 pub fn change_mutability_of_binding_in_pattern() {
     let (mut _a, _b) = (99u8, 'q');