From 6bd8b56b66026676ee2466889ba62b13c5689f71 Mon Sep 17 00:00:00 2001
From: Keno Fischer <kfischer@college.harvard.edu>
Date: Fri, 8 Aug 2014 01:28:12 -0400
Subject: [PATCH] Fix #7897

---
 src/cgutils.cpp | 10 ++++++++--
 test/core.jl    | 13 +++++++++++++
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/src/cgutils.cpp b/src/cgutils.cpp
index bae1edb922e12..94119e9f492f2 100644
--- a/src/cgutils.cpp
+++ b/src/cgutils.cpp
@@ -1520,8 +1520,14 @@ static Value *boxed(Value *v, jl_codectx_t *ctx, jl_value_t *jt)
         if (jl_subtype(jt2, jt, 0))
             jt = jt2;
     }
-
-    if (jt == jl_bottom_type || v == NULL || dyn_cast<UndefValue>(v) != 0 || t == NoopType) {
+    UndefValue *uv = NULL;
+    if (jt == jl_bottom_type || v == NULL || (uv = dyn_cast<UndefValue>(v)) != 0 || t == NoopType) {
+        if (uv != NULL && jl_is_datatype(jt)) {
+            jl_datatype_t *jb = (jl_datatype_t*)jt;
+            // We have an undef value on a hopefully dead branch
+            if (jl_isbits(jb) && jb->size != 0)
+                return UndefValue::get(jl_pvalue_llvmt);
+        }
         jl_value_t *s = static_void_instance(jt);
         if (jl_is_tuple(jt) && jl_tuple_len(jt) > 0)
             jl_add_linfo_root(ctx->linfo, s);
diff --git a/test/core.jl b/test/core.jl
index 14551b40bfba6..f26a3d1fb5d4d 100644
--- a/test/core.jl
+++ b/test/core.jl
@@ -1813,3 +1813,16 @@ type Foo7810{T<:AbstractVector}
 end
 bar7810() = [Foo7810([(a,b) for a in 1:2]) for b in 3:4]
 @test Base.return_types(bar7810,())[1] == Array{Foo7810{Array{(Int,Int),1}},1}
+
+# issue 7897
+function issue7897!(data, arr)
+    data = reinterpret(Uint32, data)
+    a = arr[1]
+end
+
+a = ones(Uint8, 10)
+sa = sub(a,4:6)
+# This can throw an error, but shouldn't segfault
+try
+    issue7897!(sa, zeros(10))
+end