From: Roman Lebedev <lebedev.ri@gmail.com>
Date: Mon, 15 Mar 2021 08:51:23 +0000 (+0300)
Subject: [NFCI][ValueTracking] getUnderlyingObject(): assert that no cycles are encountered
X-Git-Tag: llvmorg-14-init~12389
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=36f1c3db66f7268ea3183bcf0bbf05b3e1c570b4;p=platform%2Fupstream%2Fllvm.git

[NFCI][ValueTracking] getUnderlyingObject(): assert that no cycles are encountered

Jeroen Dobbelaere in
https://lists.llvm.org/pipermail/llvm-dev/2021-March/149206.html
is reporting that this function can end up in an endless loop
when called from SROA w/ full restrict patches.

For now, simply ensure that such problems are caught earlier/easier.
---

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 79399cf..8c44d73 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -4165,7 +4165,11 @@ static bool isSameUnderlyingObjectInLoop(const PHINode *PN,
 const Value *llvm::getUnderlyingObject(const Value *V, unsigned MaxLookup) {
   if (!V->getType()->isPointerTy())
     return V;
+#ifndef NDEBUG
+  SmallPtrSet<const Value *, 8> Visited;
+#endif
   for (unsigned Count = 0; MaxLookup == 0 || Count < MaxLookup; ++Count) {
+    assert(Visited.insert(V).second && "Cycle detected. Unreachable code?");
     if (auto *GEP = dyn_cast<GEPOperator>(V)) {
       V = GEP->getPointerOperand();
     } else if (Operator::getOpcode(V) == Instruction::BitCast ||