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

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Andreas Jonson (andjo403)

<details>
<summary>Changes</summary>

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.

---
Full diff: https://github.com/llvm/llvm-project/pull/128588.diff


1 Files Affected:

- (modified) llvm/lib/Transforms/Scalar/ConstraintElimination.cpp (+7-4) 


``````````diff
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 =

``````````

</details>


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