[ValueTracking] Fix crash in isGuaranteedNotToBeUndefOrPoison when V is in an unreachable block

Summary:
This fixes PR45885 by fixing isGuaranteedNotToBeUndefOrPoison so it does not look into dominating
branch conditions of V when V is an instruction in an unreachable block.

Reviewers: spatel, nikic, lebedev.ri

Reviewed By: nikic

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D79790

1 files changed, 6 insertions, 1 deletions

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 691e452..a4b0202 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -4821,12 +4821,17 @@ bool llvm::isGuaranteedNotToBeUndefOrPoison(const Value *V,
   if (!CtxI || !CtxI->getParent() || !DT)
     return false;
 
+  auto *DNode = DT->getNode(CtxI->getParent());
+  if (!DNode)
+    // Unreachable block
+    return false;
+
   // If V is used as a branch condition before reaching CtxI, V cannot be
   // undef or poison.
   //   br V, BB1, BB2
   // BB1:
   //   CtxI ; V cannot be undef or poison here
-  auto Dominator = DT->getNode(CtxI->getParent())->getIDom();
+  auto *Dominator = DNode->getIDom();
   while (Dominator) {
     auto *TI = Dominator->getBlock()->getTerminator();