From 0e34491fef992460fbfbe7d790e13bcd6d01ccb1 Mon Sep 17 00:00:00 2001
From: Tim Northover <tnorthover@apple.com>
Date: Tue, 14 Jul 2015 21:03:18 +0000
Subject: [PATCH] GVN: tolerate an instruction being replaced without existing
 in the leaderboard

Sometimes an incidentally created instruction can duplicate a Value used
elsewhere. It then often doesn't end up in the leader table. If it's later
removed, we attempt to remove it from the leader table and segfault.

Instead we should just ignore the removal request, which won't cause any
problems. The reverse situation, where the original instruction is replaced by
the new one (which you might think could leave the leader table empty) cannot
occur, because the incidental instruction will never be found in the first
place.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@242199 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/GVN.cpp       |  5 ++++-
 test/Transforms/GVN/pre-new-inst.ll | 29 +++++++++++++++++++++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)
 create mode 100644 test/Transforms/GVN/pre-new-inst.ll

diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp
index 2c47a8ab783..b1a0db356a1 100644
--- a/lib/Transforms/Scalar/GVN.cpp
+++ b/lib/Transforms/Scalar/GVN.cpp
@@ -656,11 +656,14 @@ namespace {
       LeaderTableEntry* Prev = nullptr;
       LeaderTableEntry* Curr = &LeaderTable[N];
 
-      while (Curr->Val != I || Curr->BB != BB) {
+      while (Curr && (Curr->Val != I || Curr->BB != BB)) {
         Prev = Curr;
         Curr = Curr->Next;
       }
 
+      if (!Curr)
+        return;
+
       if (Prev) {
         Prev->Next = Curr->Next;
       } else {
diff --git a/test/Transforms/GVN/pre-new-inst.ll b/test/Transforms/GVN/pre-new-inst.ll
new file mode 100644
index 00000000000..238b8a687cc
--- /dev/null
+++ b/test/Transforms/GVN/pre-new-inst.ll
@@ -0,0 +1,29 @@
+; RUN: opt -basicaa -gvn -S %s | FileCheck %s
+
+%MyStruct = type { i32, i32 }
+define i8 @foo(i64 %in, i8* %arr) {
+  %addr = alloca %MyStruct
+  %dead = trunc i64 %in to i32
+  br i1 undef, label %next, label %tmp
+
+tmp:
+  call void @bar()
+  br label %next
+
+next:
+  %addr64 = bitcast %MyStruct* %addr to i64*
+  store i64 %in, i64* %addr64
+  br label %final
+
+final:
+  %addr32 = getelementptr %MyStruct, %MyStruct* %addr, i32 0, i32 0
+  %idx32 = load i32, i32* %addr32
+
+; CHECK: %resptr = getelementptr i8, i8* %arr, i32 %dead
+  %resptr = getelementptr i8, i8* %arr, i32 %idx32
+  %res = load i8, i8* %resptr
+
+  ret i8 %res
+}
+
+declare void @bar()
-- 
2.34.1