[SLP] Improve gather tree nodes matching when users are PHIs. (#69392)

Author: Valery Dmitriev

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -9043,6 +9043,7 @@ BoUpSLP::isGatherShuffledEntry(const TreeEntry *TE, ArrayRef<Value *> VL,
   // blocks.
   if (auto *PHI = dyn_cast<PHINode>(TEUseEI.UserTE->getMainOp())) {
     TEInsertBlock = PHI->getIncomingBlock(TEUseEI.EdgeIdx);
+    TEInsertPt = TEInsertBlock->getTerminator();
   } else {
     TEInsertBlock = TEInsertPt->getParent();
   }
@@ -9106,9 +9107,10 @@ BoUpSLP::isGatherShuffledEntry(const TreeEntry *TE, ArrayRef<Value *> VL,
       const Instruction *InsertPt =
           UserPHI ? UserPHI->getIncomingBlock(UseEI.EdgeIdx)->getTerminator()
                   : &getLastInstructionInBundle(UseEI.UserTE);
-      if (!UserPHI && TEInsertPt == InsertPt) {
-        // If 2 gathers are operands of the same non-PHI entry,
-        // compare operands indices, use the earlier one as the base.
+      if (TEInsertPt == InsertPt) {
+        // If 2 gathers are operands of the same entry (regardless of wether
+        // user is PHI or else), compare operands indices, use the earlier one
+        // as the base.
         if (TEUseEI.UserTE == UseEI.UserTE && TEUseEI.EdgeIdx < UseEI.EdgeIdx)
           continue;
         // If the user instruction is used for some reason in different

llvm/test/Transforms/SLPVectorizer/X86/matching-gather-nodes-phi-users.ll

@@ -8,7 +8,7 @@
 ; YAML: Function:        test
 ; YAML: Args:
 ; YAML:   - String:          'Stores SLP vectorized with cost '
-; YAML:   - Cost:            '-3'
+; YAML:   - Cost:            '-6'
 ; YAML:   - String:          ' and with tree size '
 ; YAML:   - TreeSize:        '14'
 ; YAML: ...