[llvm] [SLP]Make PHICompare comparator follow weak strict ordering requirement (PR #110529)

[Eli Friedman via llvm-commits]

================
@@ -5458,21 +5485,60 @@ BoUpSLP::getReorderingData(const TreeEntry &TE, bool TopToBottom) {
         return false;
       auto *FirstUserOfPhi1 = cast<Instruction>(*V1->user_begin());
       auto *FirstUserOfPhi2 = cast<Instruction>(*V2->user_begin());
-      if (auto *IE1 = dyn_cast<InsertElementInst>(FirstUserOfPhi1))
-        if (auto *IE2 = dyn_cast<InsertElementInst>(FirstUserOfPhi2)) {
-          if (!areTwoInsertFromSameBuildVector(
-                  IE1, IE2,
-                  [](InsertElementInst *II) { return II->getOperand(0); }))
-            return I1 < I2;
+      if (FirstUserOfPhi1->getParent() != FirstUserOfPhi2->getParent())
+        return CompareByBasicBlocks(FirstUserOfPhi1->getParent(),
+                                    FirstUserOfPhi2->getParent());
+      auto *IE1 = dyn_cast<InsertElementInst>(FirstUserOfPhi1);
+      auto *IE2 = dyn_cast<InsertElementInst>(FirstUserOfPhi2);
+      auto *EE1 = dyn_cast<ExtractElementInst>(FirstUserOfPhi1);
+      auto *EE2 = dyn_cast<ExtractElementInst>(FirstUserOfPhi2);
+      if (IE1 && !IE2)
+        return true;
+      if (!IE1 && IE2)
+        return false;
+      if (IE1 && IE2) {
+        if (UserBVHead[I1] && !UserBVHead[I2])
+          return true;
+        if (!UserBVHead[I1])
+          return false;
+        if (UserBVHead[I1] == UserBVHead[I2])
           return getElementIndex(IE1) < getElementIndex(IE2);
-        }
-      if (auto *EE1 = dyn_cast<ExtractElementInst>(FirstUserOfPhi1))
-        if (auto *EE2 = dyn_cast<ExtractElementInst>(FirstUserOfPhi2)) {
-          if (EE1->getOperand(0) != EE2->getOperand(0))
-            return I1 < I2;
+        if (UserBVHead[I1]->getParent() != UserBVHead[I2]->getParent())
+          return CompareByBasicBlocks(UserBVHead[I1]->getParent(),
+                                      UserBVHead[I2]->getParent());
+        return UserBVHead[I1]->comesBefore(UserBVHead[I2]);
+      }
+      if (EE1 && !EE2)
+        return true;
+      if (!EE1 && EE2)
+        return false;
+      if (EE1 && EE2) {
+        auto *Inst1 = dyn_cast<Instruction>(EE1->getOperand(0));
+        auto *Inst2 = dyn_cast<Instruction>(EE2->getOperand(0));
+        auto *P1 = dyn_cast<Argument>(EE1->getOperand(0));
+        auto *P2 = dyn_cast<Argument>(EE2->getOperand(0));
+        if ((!Inst1 && !Inst2) || (!P1 && !P2))
----------------
efriedma-quic wrote:

```suggestion
        if (!Inst2 && !P2)
          return Inst1 || P1;
```

https://github.com/llvm/llvm-project/pull/110529