Rollup merge of #68911 - jonas-schievink:inherent-overlap, r=petrochenkov

[rust.git] / src / librustc_passes / liveness.rs

diff --git a/src/librustc_passes/liveness.rs b/src/librustc_passes/liveness.rs
index 7718139f6e9246af2b0eb2ef03781ee4c3de31e6..b355a47c39470559e5431d220e3349299b9dd280 100644 (file)
--- a/src/librustc_passes/liveness.rs
+++ b/src/librustc_passes/liveness.rs
@@ -822,8 +822,15 @@ fn merge_from_succ(&mut self, ln: LiveNode, succ_ln: LiveNode, first_merge: bool
             return false;
         }
 
-        let mut changed = false;
+        let mut any_changed = false;
         self.indices2(ln, succ_ln, |this, idx, succ_idx| {
+            // This is a special case, pulled out from the code below, where we
+            // don't have to do anything. It occurs about 60-70% of the time.
+            if this.rwu_table.packed_rwus[succ_idx] == INV_INV_FALSE {
+                return;
+            }
+
+            let mut changed = false;
             let mut rwu = this.rwu_table.get(idx);
             let succ_rwu = this.rwu_table.get(succ_idx);
             if succ_rwu.reader.is_valid() && !rwu.reader.is_valid() {
@@ -843,6 +850,7 @@ fn merge_from_succ(&mut self, ln: LiveNode, succ_ln: LiveNode, first_merge: bool
 
             if changed {
                 this.rwu_table.assign_unpacked(idx, rwu);
+                any_changed = true;
             }
         });
 
@@ -851,9 +859,9 @@ fn merge_from_succ(&mut self, ln: LiveNode, succ_ln: LiveNode, first_merge: bool
             ln,
             self.ln_str(succ_ln),
             first_merge,
-            changed
+            any_changed
         );
-        return changed;
+        return any_changed;
     }
 
     // Indicates that a local variable was *defined*; we know that no