From f3d4166368b0449baea1e7d8e043d0fe76930179 Mon Sep 17 00:00:00 2001
From: Nikita Popov <nikita.ppv@gmail.com>
Date: Sun, 29 Mar 2020 22:10:31 +0200
Subject: [PATCH] [InstCombine] Report change in non zero phi transform

We need to inform InstCombine (and transitively the pass manager)
that we changed an instruction.
---
 llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp b/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
index 6c2aead..9cdb68d 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
@@ -1194,15 +1194,22 @@ Instruction *InstCombiner::visitPHINode(PHINode &PN) {
     if (CmpInst && isa<IntegerType>(PN.getType()) && CmpInst->isEquality() &&
         match(CmpInst->getOperand(1), m_Zero())) {
       ConstantInt *NonZeroConst = nullptr;
+      bool MadeChange = false;
       for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
         Instruction *CtxI = PN.getIncomingBlock(i)->getTerminator();
         Value *VA = PN.getIncomingValue(i);
         if (isKnownNonZero(VA, DL, 0, &AC, CtxI, &DT)) {
           if (!NonZeroConst)
             NonZeroConst = GetAnyNonZeroConstInt(PN);
-          PN.setIncomingValue(i, NonZeroConst);
+
+          if (NonZeroConst != VA) {
+            PN.setIncomingValue(i, NonZeroConst);
+            MadeChange = true;
+          }
         }
       }
+      if (MadeChange)
+        return &PN;
     }
   }
 
-- 
2.7.4