[llvm] [SCCP] Improve worklist management (PR #146321)

[Yingwei Zheng via llvm-commits]

================
@@ -985,27 +953,49 @@ bool SCCPInstVisitor::markBlockExecutable(BasicBlock *BB) {
   return true;
 }
 
-void SCCPInstVisitor::pushToWorkList(ValueLatticeElement &IV, Value *V) {
-  if (IV.isOverdefined()) {
-    if (OverdefinedInstWorkList.empty() || OverdefinedInstWorkList.back() != V)
-      OverdefinedInstWorkList.push_back(V);
+void SCCPInstVisitor::pushToWorkList(Instruction *I) {
+  // If we're currently visiting a block, do not push any instructions in the
+  // same blocks that are after the current one, as they will be visited
+  // anyway. We do have to push updates to earlier instructions (e.g. phi
+  // nodes or loads of tracked globals).
+  if (CurI && I->getParent() == CurI->getParent() && !I->comesBefore(CurI))
     return;
+  // Only push instructions in already visited blocks. Otherwise we'll handle
+  // it when we visit the block for the first time.
+  if (BBVisited.count(I->getParent()))
----------------
dtcxzyw wrote:

```suggestion
  if (BBVisited.contains(I->getParent()))
```

https://github.com/llvm/llvm-project/pull/146321