[llvm-branch-commits] [llvm] [SSAUpdaterBulk] Add PHI simplification pass. (PR #135180)

[Matt Arsenault via llvm-branch-commits]

================
@@ -222,3 +223,38 @@ void SSAUpdaterBulk::RewriteAllUses(DominatorTree *DT,
     }
   }
 }
+
+// Perform a single pass of simplification over the worklist of PHIs.
+static void SimplifyPass(MutableArrayRef<PHINode *> Worklist) {
+  if (Worklist.empty())
+    return;
+
+  const DataLayout &DL = Worklist.front()->getParent()->getDataLayout();
+  for (PHINode *&PHI : Worklist) {
+    if (Value *Simplified = simplifyInstruction(PHI, DL)) {
+      PHI->replaceAllUsesWith(Simplified);
+      PHI->eraseFromParent();
+      PHI = nullptr; // Mark as removed.
+    }
+  }
+}
+
+static void DeduplicatePass(ArrayRef<PHINode *> Worklist) {
+  SmallDenseMap<BasicBlock *, unsigned> BBs;
+  for (PHINode *PHI : Worklist) {
+    if (PHI)
+      ++BBs[PHI->getParent()];
+  }
+
+  for (auto [BB, NumNewPHIs] : BBs) {
+    auto FirstExistedPN = std::next(BB->phis().begin(), NumNewPHIs);
+    EliminateNewDuplicatePHINodes(BB, FirstExistedPN);
+  }
+}
+
+void SSAUpdaterBulk::RewriteAndOptimizeAllUses(DominatorTree *DT) {
+  SmallVector<PHINode *, 4> PHIs;
+  RewriteAllUses(DT, &PHIs);
+  SimplifyPass(PHIs);
+  DeduplicatePass(PHIs);
+}
----------------
arsenm wrote:

```suggestion
}

```

https://github.com/llvm/llvm-project/pull/135180