2017-10-13  Jakub Jelinek  <jakub@redhat.com>

	PR target/82274

	* libgcc2.c (__mulvDI3): If both operands have

	the same highpart of -1 and the topmost bit of lowpart is 0,

	multiplication overflows even if both lowparts are 0.

	* gcc.dg/pr82274-1.c: New test.

--- libgcc/libgcc2.c	2017/10/13 16:50:13	253733

+++ libgcc/libgcc2.c	2017/10/13 17:19:12	253734

@@ -375,7 +375,8 @@

 		}

 	      else

 		{

-		  if (uu.s.high == (Wtype) -1 && vv.s.high == (Wtype) - 1)

+		  if ((uu.s.high & vv.s.high) == (Wtype) -1

+		      && (uu.s.low | vv.s.low) != 0)

 		    {

 		      DWunion ww = {.ll = (UDWtype) (UWtype) uu.s.low

 				    * (UDWtype) (UWtype) vv.s.low};

--- /dev/null

+++ gcc/testsuite/gcc.dg/pr82274-1.c

@@ -0,0 +1,16 @@

+/* PR target/82274 */

+/* { dg-do run } */

+/* { dg-shouldfail "trapv" } */

+/* { dg-options "-ftrapv" } */

+

+int

+main ()

+{

+#ifdef __SIZEOF_INT128__

+  volatile __int128 m = -(((__int128) 1) << (__CHAR_BIT__ * __SIZEOF_INT128__ / 2));

+#else

+  volatile long long m = -(1LL << (__CHAR_BIT__ * __SIZEOF_LONG_LONG__ / 2));

+#endif

+  m = m * m;

+  return 0;

+}