RFR: 8345287: C2: live in computation is broken

[Roland Westrelin]

8234003 (Improve IndexSet iteration) broke live in computation:


@@ -273,23 +276,25 @@ void PhaseLive::add_liveout( Block *p, IndexSet *lo, VectorSet &first_pass ) {
 // Add a vector of live-in values to a given blocks live-in set.
 void PhaseLive::add_livein(Block *p, IndexSet *lo) {
   IndexSet *livein = &_livein[p->_pre_order-1];
-  IndexSetIterator elements(lo);
-  uint r;
-  while ((r = elements.next()) != 0) {
-    livein->insert(r);         // Then add to live-in set
+  if (!livein->is_empty()) {
+    IndexSetIterator elements(lo);
+    uint r;
+    while ((r = elements.next()) != 0) {
+      livein->insert(r);         // Then add to live-in set
+    }
   }
 }


`livein` is initially empy and the patch above only adds element to it if:


if (!livein->is_empty()) {


which is never true.

This doesn't affect correctness as live in sets are only used to drive
scheduling.

-------------

Commit messages:
 - fix

Changes: https://git.openjdk.org/jdk/pull/22473/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22473&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345287
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/22473.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22473/head:pull/22473

PR: https://git.openjdk.org/jdk/pull/22473