From c20535dff6680917835a365624da67027a8fae53 Mon Sep 17 00:00:00 2001
From: Owen Anderson <resistor@mac.com>
Date: Fri, 13 Mar 2015 07:09:33 +0000
Subject: [PATCH] Teach TBAA analysis to report errors on cyclic TBAA metadata
 rather than hanging.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232144 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/TypeBasedAliasAnalysis.cpp       | 13 +++++++---
 .../Analysis/TypeBasedAliasAnalysis/cyclic.ll | 26 +++++++++++++++++++
 2 files changed, 35 insertions(+), 4 deletions(-)
 create mode 100644 test/Analysis/TypeBasedAliasAnalysis/cyclic.ll

diff --git a/lib/Analysis/TypeBasedAliasAnalysis.cpp b/lib/Analysis/TypeBasedAliasAnalysis.cpp
index 1ed2653bee9..115872584cb 100644
--- a/lib/Analysis/TypeBasedAliasAnalysis.cpp
+++ b/lib/Analysis/TypeBasedAliasAnalysis.cpp
@@ -129,6 +129,7 @@
 #include "llvm/IR/Module.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/ADT/SetVector.h"
 using namespace llvm;
 
 // A handy option for disabling TBAA functionality. The same effect can also be
@@ -578,18 +579,22 @@ MDNode *MDNode::getMostGenericTBAA(MDNode *A, MDNode *B) {
     if (!B) return nullptr;
   }
 
-  SmallVector<MDNode *, 4> PathA;
+  SmallSetVector<MDNode *, 4> PathA;
   MDNode *T = A;
   while (T) {
-    PathA.push_back(T);
+    if (PathA.count(T))
+      report_fatal_error("Cycle found in TBAA metadata.");
+    PathA.insert(T);
     T = T->getNumOperands() >= 2 ? cast_or_null<MDNode>(T->getOperand(1))
                                  : nullptr;
   }
 
-  SmallVector<MDNode *, 4> PathB;
+  SmallSetVector<MDNode *, 4> PathB;
   T = B;
   while (T) {
-    PathB.push_back(T);
+    if (PathB.count(T))
+      report_fatal_error("Cycle found in TBAA metadata.");
+    PathB.insert(T);
     T = T->getNumOperands() >= 2 ? cast_or_null<MDNode>(T->getOperand(1))
                                  : nullptr;
   }
diff --git a/test/Analysis/TypeBasedAliasAnalysis/cyclic.ll b/test/Analysis/TypeBasedAliasAnalysis/cyclic.ll
new file mode 100644
index 00000000000..a88e26c5cd5
--- /dev/null
+++ b/test/Analysis/TypeBasedAliasAnalysis/cyclic.ll
@@ -0,0 +1,26 @@
+; RUN: not opt -instcombine < %s 2>&1 | FileCheck %s
+; CHECK: Cycle found in TBAA metadata.
+
+define void @test6(i32* %gi) #0 {
+entry:
+  store i32 42, i32* %gi, align 4, !tbaa !0
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.body, %entry
+  br i1 undef, label %for.body, label %for.end
+
+for.body:                                         ; preds = %for.cond
+  store i32 undef, i32* %gi, align 4, !tbaa !2
+  br label %for.cond
+
+for.end:                                          ; preds = %for.cond
+  ret void
+}
+
+attributes #0 = { nounwind ssp uwtable }
+
+!0 = !{!1, !1, i64 0}
+!1 = !{!"Simple C/C++ TBAA"}
+!2 = distinct !{!3, !2, i64 0}
+!3 = !{!"int", !4}
+!4 = !{!"omnipotent ", !1}