PR78629

[Prathamesh Kulkarni]

Hi Richard,
I tested your fix for the patch with ubsan stage-1 built gcc, and it
fixes the error.
Is it OK to commit if bootstrap+test passes on x86_64-unknown-linux-gnu ?

Thanks,
Prathamesh

2016-12-01  Richard Biener  <rguent...@suse.de>
            Prathamesh Kulkarni  <prathamesh.kulka...@linaro.org>

        PR middle-end/78629
        * vec.h (vec<T, A, vl_embed>::quick_grow_cleared): Guard call to
        memset if len-oldlen != 0.
        (vec<T, va_heap, vl_ptr>::safe_grow_cleared): Likewise.

diff --git a/gcc/vec.h b/gcc/vec.h
index 14fb2a6..aa93411 100644
--- a/gcc/vec.h
+++ b/gcc/vec.h
@@ -1092,8 +1092,10 @@ inline void
 vec<T, A, vl_embed>::quick_grow_cleared (unsigned len)
 {
   unsigned oldlen = length ();
+  size_t sz = sizeof (T) * (len - oldlen);
   quick_grow (len);
-  memset (&(address ()[oldlen]), 0, sizeof (T) * (len - oldlen));
+  if (sz != 0)
+    memset (&(address ()[oldlen]), 0, sz);
 }
 
 
@@ -1605,8 +1607,10 @@ inline void
 vec<T, va_heap, vl_ptr>::safe_grow_cleared (unsigned len MEM_STAT_DECL)
 {
   unsigned oldlen = length ();
+  size_t sz = sizeof (T) * (len - oldlen);
   safe_grow (len PASS_MEM_STAT);
-  memset (&(address ()[oldlen]), 0, sizeof (T) * (len - oldlen));
+  if (sz != 0)
+    memset (&(address ()[oldlen]), 0, sz);
 }