[llvm] [InstCombine] Push freeze through non-recurrence PHIs (PR #157678)

[David Sherwood via llvm-commits]

================
@@ -5042,10 +5042,33 @@ InstCombinerImpl::pushFreezeToPreventPoisonFromPropagating(FreezeInst &OrigFI) {
   //   Op1.fr = Freeze(Op1)
   //   ... = Inst(Op1.fr, NonPoisonOps...)
 
-  auto CanPushFreeze = [](Value *V) {
-    if (!isa<Instruction>(V) || isa<PHINode>(V))
+  auto CanPushFreeze = [this](Value *V) {
+    if (!isa<Instruction>(V))
       return false;
 
+    if (auto *PN = dyn_cast<PHINode>(V)) {
+      BasicBlock *BB = PN->getParent();
+      SmallPtrSet<BasicBlock *, 8> VisitedBBs;
+      for (Use &U : PN->incoming_values()) {
----------------
david-arm wrote:

You might be able to avoid the additional cost of a lookup in `getIncomingBlock` below by rewriting the loop like this:

```
  for (unsigned I = 0; I < PN->getNumIncomingValues(); I++) {
    Value *InV = PN->getIncomingValue(I);
    BasicBlock *InBB = PN->getIncomingBlock(I);
  }
```

https://github.com/llvm/llvm-project/pull/157678