[llvm] [SCEV] Avoid redundant stack push/pop in createSCEVIter (PR #199352)

[via llvm-commits]

https://github.com/daemonpilot updated https://github.com/llvm/llvm-project/pull/199352

>From f87c3daa0e3f38c612675d898ebc3449cdf14146 Mon Sep 17 00:00:00 2001
From: daemonpilot <daemonpilot at hotmail.com>
Date: Sat, 23 May 2026 22:09:43 +0800
Subject: [PATCH] [SCEV] Avoid redundant stack push/pop in createSCEVIter

---
 llvm/lib/Analysis/ScalarEvolution.cpp | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index c93838ffdc50d..29f34392358bc 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -7729,14 +7729,15 @@ const SCEV *ScalarEvolution::createSCEVIter(Value *V) {
   using PointerTy = PointerIntPair<Value *, 1, bool>;
   SmallVector<PointerTy> Stack;
 
-  Stack.emplace_back(V, true);
   Stack.emplace_back(V, false);
   while (!Stack.empty()) {
-    auto E = Stack.pop_back_val();
+    auto E = Stack.back();
     Value *CurV = E.getPointer();
 
-    if (getExistingSCEV(CurV))
+    if (getExistingSCEV(CurV)) {
+      Stack.pop_back();
       continue;
+    }
 
     SmallVector<Value *> Ops;
     const SCEV *CreatedSCEV = nullptr;
@@ -7752,10 +7753,10 @@ const SCEV *ScalarEvolution::createSCEVIter(Value *V) {
 
     if (CreatedSCEV) {
       insertValueToMap(CurV, CreatedSCEV);
+      Stack.pop_back();
     } else {
-      // Queue CurV for SCEV creation, followed by its's operands which need to
-      // be constructed first.
-      Stack.emplace_back(CurV, true);
+      Stack.back().setInt(true);
+      // Queue its operands which need to be constructed.
       for (Value *Op : Ops)
         Stack.emplace_back(Op, false);
     }