[llvm] [ConstraintElim] Preserve analyses when IR is unchanged. (PR #128588)

[Andreas Jonson via llvm-commits]

https://github.com/andjo403 created https://github.com/llvm/llvm-project/pull/128588

Noticed that all Analys passes was not preserved for unchanged IR when the test was containing assumes.

`PreservedAnalyses::all()` is not called for E.g.  https://github.com/andjo403/llvm-project/blob/e24bb833b1af521fc2aec997a8b89de795b34449/llvm/test/Transforms/ConstraintElimination/mul.ll#L283-L301

Not sure how to/if possible to add a test for this.

>From cf3be5b7813730148aabccabbd9e7967315aa6f8 Mon Sep 17 00:00:00 2001
From: Andreas Jonson <andjo403 at hotmail.com>
Date: Mon, 24 Feb 2025 23:33:22 +0100
Subject: [PATCH] [ConstraintElim] Preserve analyses when IR is unchanged.

---
 llvm/lib/Transforms/Scalar/ConstraintElimination.cpp | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
index 79f6858463d7e..267eb319a5616 100644
--- a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
@@ -1435,8 +1435,9 @@ static bool checkAndReplaceCondition(
     generateReproducer(Cmp, ReproducerModule, ReproducerCondStack, Info, DT);
     Constant *ConstantC = ConstantInt::getBool(
         CmpInst::makeCmpResultType(Cmp->getType()), IsTrue);
-    Cmp->replaceUsesWithIf(ConstantC, [&DT, NumIn, NumOut,
-                                       ContextInst](Use &U) {
+    bool Changed = false;
+    Cmp->replaceUsesWithIf(ConstantC, [&DT, NumIn, NumOut, ContextInst,
+                                       &Changed](Use &U) {
       auto *UserI = getContextInstForUse(U);
       auto *DTN = DT.getNode(UserI->getParent());
       if (!DTN || DTN->getDFSNumIn() < NumIn || DTN->getDFSNumOut() > NumOut)
@@ -1448,12 +1449,14 @@ static bool checkAndReplaceCondition(
       // Conditions in an assume trivially simplify to true. Skip uses
       // in assume calls to not destroy the available information.
       auto *II = dyn_cast<IntrinsicInst>(U.getUser());
-      return !II || II->getIntrinsicID() != Intrinsic::assume;
+      bool ShouldReplace = !II || II->getIntrinsicID() != Intrinsic::assume;
+      Changed |= ShouldReplace;
+      return ShouldReplace;
     });
     NumCondsRemoved++;
     if (Cmp->use_empty())
       ToRemove.push_back(Cmp);
-    return true;
+    return Changed;
   };
 
   if (auto ImpliedCondition =