[llvm] (Draft) [SimplifyIndVar] Push more users to worklist for simplifyUsers (PR #93598)

[via llvm-commits]

https://github.com/v01dXYZ created https://github.com/llvm/llvm-project/pull/93598

Instead of considering only users that are inside the loop, consider all the users with parent dominated by the loop header.

This is a draft PR to discuss about the code  before doing some QA. @etherzhhb Do you think my code is valid ?

>From 4306f3b479701ce410ce2fb9b990fe80ebff3f8d Mon Sep 17 00:00:00 2001
From: v01dxyz <v01dxyz at v01d.xyz>
Date: Mon, 27 May 2024 11:31:21 +0200
Subject: [PATCH] (Draft) [SimplifyIndVar] Push more users to worklist for
 simplifyUsers

Instead of considering only users that are inside the loop,
consider all the users with parent dominated by the loop header.
---
 llvm/lib/Transforms/Utils/SimplifyIndVar.cpp | 22 ++++++++++----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
index 912c02c2ed3ae..decdf27125f58 100644
--- a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
@@ -840,9 +840,9 @@ bool SimplifyIndvar::strengthenRightShift(BinaryOperator *BO,
 
 /// Add all uses of Def to the current IV's worklist.
 static void pushIVUsers(
-  Instruction *Def, Loop *L,
-  SmallPtrSet<Instruction*,16> &Simplified,
-  SmallVectorImpl< std::pair<Instruction*,Instruction*> > &SimpleIVUsers) {
+    Instruction *Def, Loop *L, DominatorTree *DT,
+    SmallPtrSet<Instruction *, 16> &Simplified,
+    SmallVectorImpl<std::pair<Instruction *, Instruction *>> &SimpleIVUsers) {
 
   for (User *U : Def->users()) {
     Instruction *UI = cast<Instruction>(U);
@@ -854,9 +854,9 @@ static void pushIVUsers(
     if (UI == Def)
       continue;
 
-    // Only change the current Loop, do not change the other parts (e.g. other
-    // Loops).
-    if (!L->contains(UI))
+    // Avoid adding Defs that SCEV expand to themselves, e.g. the LoopPhis
+    // of the outter loops.
+    if (!DT->dominates(L->getHeader(), UI->getParent()))
       continue;
 
     // Do not push the same instruction more than once.
@@ -913,7 +913,7 @@ void SimplifyIndvar::simplifyUsers(PHINode *CurrIV, IVVisitor *V) {
   // Push users of the current LoopPhi. In rare cases, pushIVUsers may be
   // called multiple times for the same LoopPhi. This is the proper thing to
   // do for loop header phis that use each other.
-  pushIVUsers(CurrIV, L, Simplified, SimpleIVUsers);
+  pushIVUsers(CurrIV, L, DT, Simplified, SimpleIVUsers);
 
   while (!SimpleIVUsers.empty()) {
     std::pair<Instruction*, Instruction*> UseOper =
@@ -960,7 +960,7 @@ void SimplifyIndvar::simplifyUsers(PHINode *CurrIV, IVVisitor *V) {
       continue;
 
     if (eliminateIVUser(UseInst, IVOperand)) {
-      pushIVUsers(IVOperand, L, Simplified, SimpleIVUsers);
+      pushIVUsers(IVOperand, L, DT, Simplified, SimpleIVUsers);
       continue;
     }
 
@@ -968,14 +968,14 @@ void SimplifyIndvar::simplifyUsers(PHINode *CurrIV, IVVisitor *V) {
       if (strengthenBinaryOp(BO, IVOperand)) {
         // re-queue uses of the now modified binary operator and fall
         // through to the checks that remain.
-        pushIVUsers(IVOperand, L, Simplified, SimpleIVUsers);
+        pushIVUsers(IVOperand, L, DT, Simplified, SimpleIVUsers);
       }
     }
 
     // Try to use integer induction for FPToSI of float induction directly.
     if (replaceFloatIVWithIntegerIV(UseInst)) {
       // Re-queue the potentially new direct uses of IVOperand.
-      pushIVUsers(IVOperand, L, Simplified, SimpleIVUsers);
+      pushIVUsers(IVOperand, L, DT, Simplified, SimpleIVUsers);
       continue;
     }
 
@@ -985,7 +985,7 @@ void SimplifyIndvar::simplifyUsers(PHINode *CurrIV, IVVisitor *V) {
       continue;
     }
     if (isSimpleIVUser(UseInst, L, SE)) {
-      pushIVUsers(UseInst, L, Simplified, SimpleIVUsers);
+      pushIVUsers(UseInst, L, DT, Simplified, SimpleIVUsers);
     }
   }
 }