inliner: Copy unevaluated constants only after successful inlining

Inliner copies the unevaluated constants from the callee body to the
caller at the point where decision to inline is yet to be made. The
constants will be unnecessary if inlining were to fail.

Organize the code moving items from callee to the caller together in one
place to avoid the issue.

Author: tmiasko

compiler/rustc_mir/src/transform/inline.rs

@@ -140,14 +140,6 @@ impl Inliner<'tcx> {
                 continue;
             };
 
-            // Copy only unevaluated constants from the callee_body into the caller_body.
-            // Although we are only pushing `ConstKind::Unevaluated` consts to
-            // `required_consts`, here we may not only have `ConstKind::Unevaluated`
-            // because we are calling `subst_and_normalize_erasing_regions`.
-            caller_body.required_consts.extend(callee_body.required_consts.iter().copied().filter(
-                |&constant| matches!(constant.literal.val, ConstKind::Unevaluated(_, _, _)),
-            ));
-
             let start = caller_body.basic_blocks().len();
             debug!("attempting to inline callsite {:?} - body={:?}", callsite, callee_body);
             if !self.inline_call(callsite, caller_body, callee_body) {
@@ -522,6 +514,16 @@ impl Inliner<'tcx> {
                     kind: TerminatorKind::Goto { target: integrator.map_block(START_BLOCK) },
                 });
 
+                // Copy only unevaluated constants from the callee_body into the caller_body.
+                // Although we are only pushing `ConstKind::Unevaluated` consts to
+                // `required_consts`, here we may not only have `ConstKind::Unevaluated`
+                // because we are calling `subst_and_normalize_erasing_regions`.
+                caller_body.required_consts.extend(
+                    callee_body.required_consts.iter().copied().filter(|&constant| {
+                        matches!(constant.literal.val, ConstKind::Unevaluated(_, _, _))
+                    }),
+                );
+
                 true
             }
             kind => {