[llvm] [VPlan] Free removeDeadRecipes from VPPhi simplification (PR #156438)

[Ramkumar Ramachandra via llvm-commits]

https://github.com/artagnon updated https://github.com/llvm/llvm-project/pull/156438

>From 6c7b401cf082c3a85a37b57d7281dea0e685dea9 Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <ramkumar.ramachandra at codasip.com>
Date: Tue, 2 Sep 2025 11:28:21 +0100
Subject: [PATCH 1/2] [VPlan] Free removeDeadRecipes from VPPhi simplification

VPPhi simplification is best done in simplifyRecipe.
---
 .../Transforms/Vectorize/VPlanTransforms.cpp  | 29 ++++++++-----------
 llvm/lib/Transforms/Vectorize/VPlanValue.h    |  4 +++
 2 files changed, 16 insertions(+), 17 deletions(-)

diff --git a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
index 3a918ffdf5e91..b1a6940272691 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
+++ b/llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp
@@ -555,24 +555,9 @@ void VPlanTransforms::removeDeadRecipes(VPlan &Plan) {
            vp_post_order_deep(Plan.getEntry()))) {
     // The recipes in the block are processed in reverse order, to catch chains
     // of dead recipes.
-    for (VPRecipeBase &R : make_early_inc_range(reverse(*VPBB))) {
-      if (isDeadRecipe(R)) {
+    for (VPRecipeBase &R : make_early_inc_range(reverse(*VPBB)))
+      if (isDeadRecipe(R))
         R.eraseFromParent();
-        continue;
-      }
-
-      // Check if R is a dead VPPhi <-> update cycle and remove it.
-      auto *PhiR = dyn_cast<VPPhi>(&R);
-      if (!PhiR || PhiR->getNumOperands() != 2 || PhiR->getNumUsers() != 1)
-        continue;
-      VPValue *Incoming = PhiR->getOperand(1);
-      if (*PhiR->user_begin() != Incoming->getDefiningRecipe() ||
-          Incoming->getNumUsers() != 1)
-        continue;
-      PhiR->replaceAllUsesWith(PhiR->getOperand(0));
-      PhiR->eraseFromParent();
-      Incoming->getDefiningRecipe()->eraseFromParent();
-    }
   }
 }
 
@@ -1215,6 +1200,16 @@ static void simplifyRecipe(VPRecipeBase &R, VPTypeAnalysis &TypeInfo) {
   if (auto *Phi = dyn_cast<VPPhi>(Def)) {
     if (Phi->getNumOperands() == 1)
       Phi->replaceAllUsesWith(Phi->getOperand(0));
+
+    if (Phi->getNumOperands() == 2) {
+      VPValue *Incoming = Phi->getOperand(1);
+      VPUser *U = Phi->getUniqueUser();
+      if (U && U == Incoming->getDefiningRecipe() && Incoming->hasOneUser()) {
+        Phi->replaceAllUsesWith(Phi->getOperand(0));
+        Phi->eraseFromParent();
+        Incoming->getDefiningRecipe()->eraseFromParent();
+      }
+    }
     return;
   }
 
diff --git a/llvm/lib/Transforms/Vectorize/VPlanValue.h b/llvm/lib/Transforms/Vectorize/VPlanValue.h
index 24f6d61512ef6..ed6abb67493f5 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanValue.h
+++ b/llvm/lib/Transforms/Vectorize/VPlanValue.h
@@ -111,6 +111,10 @@ class LLVM_ABI_FOR_TEST VPValue {
 #endif
 
   unsigned getNumUsers() const { return Users.size(); }
+  bool hasOneUser() const { return Users.size() == 1; }
+  VPUser *getUniqueUser() const {
+    return Users.size() == 1 ? Users.front() : nullptr;
+  }
   void addUser(VPUser &User) { Users.push_back(&User); }
 
   /// Remove a single \p User from the list of users.

>From 23b0fcd152e131c9b22a10ab6ad976b87c84521d Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <ramkumar.ramachandra at codasip.com>
Date: Tue, 2 Sep 2025 11:44:40 +0100
Subject: [PATCH 2/2] [VPlan] Small improvement (NFC)

---
 llvm/lib/Transforms/Vectorize/VPlanValue.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/llvm/lib/Transforms/Vectorize/VPlanValue.h b/llvm/lib/Transforms/Vectorize/VPlanValue.h
index ed6abb67493f5..2072c5df31309 100644
--- a/llvm/lib/Transforms/Vectorize/VPlanValue.h
+++ b/llvm/lib/Transforms/Vectorize/VPlanValue.h
@@ -113,7 +113,7 @@ class LLVM_ABI_FOR_TEST VPValue {
   unsigned getNumUsers() const { return Users.size(); }
   bool hasOneUser() const { return Users.size() == 1; }
   VPUser *getUniqueUser() const {
-    return Users.size() == 1 ? Users.front() : nullptr;
+    return hasOneUser() ? Users.front() : nullptr;
   }
   void addUser(VPUser &User) { Users.push_back(&User); }