PR tree-optimization/78170: Truncate sign-extended padding when encoding bitfields

	PR tree-optimization/78170
	* gimple-ssa-store-merging.c (encode_tree_to_bitpos): Truncate padding
	introduced by native_encode_expr on little-endian as well.

	* gcc.c-torture/execute/pr78170.c: New test.

From-SVN: r241779

gcc/ChangeLog

 2016-11-02  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
 
+	PR tree-optimization/78170
+	* gimple-ssa-store-merging.c (encode_tree_to_bitpos): Truncate padding
+	introduced by native_encode_expr on little-endian as well.
+
+2016-11-02  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
+
 	PR tree-optimization/78162
 	* gimple-ssa-store-merging.c (execute): Mark stores with bitpos < 0
 	as invalid.

gcc/gimple-ssa-store-merging.c

@@ -432,13 +432,23 @@ encode_tree_to_bitpos (tree expr, unsigned char *ptr, int bitlen, int bitpos,
      contain a sign bit due to sign-extension).  */
   unsigned int padding
     = byte_size - ROUND_UP (bitlen, BITS_PER_UNIT) / BITS_PER_UNIT - 1;
-  if (BYTES_BIG_ENDIAN)
+  if (padding != 0)
     {
-      tmpbuf += padding;
+      /* On big-endian the padding is at the 'front' so just skip the initial
+	 bytes.  */
+      if (BYTES_BIG_ENDIAN)
+	tmpbuf += padding;
+
       byte_size -= padding;
       if (bitlen % BITS_PER_UNIT != 0)
-	clear_bit_region_be (tmpbuf, BITS_PER_UNIT - 1,
-			     BITS_PER_UNIT - (bitlen % BITS_PER_UNIT));
+	{
+	  if (BYTES_BIG_ENDIAN)
+	    clear_bit_region_be (tmpbuf, BITS_PER_UNIT - 1,
+				 BITS_PER_UNIT - (bitlen % BITS_PER_UNIT));
+	  else
+	    clear_bit_region (tmpbuf, bitlen,
+			      byte_size * BITS_PER_UNIT - bitlen);
+	}
     }
 
   /* Clear the bit region in PTR where the bits from TMPBUF will be

gcc/testsuite/ChangeLog

 2016-11-02  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
 
+	PR tree-optimization/78170
+	* gcc.c-torture/execute/pr78170.c: New test.
+
+2016-11-02  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
+
 	PR tree-optimization/78162
 	* gcc.c-torture/compile/pr78162.c: New test.
 

gcc/testsuite/gcc.c-torture/execute/pr78170.c

+/* PR tree-optimization/78170.
+   Check that sign-extended store to a bitfield
+   doesn't overwrite other fields.  */
+
+int a, b, d;
+
+struct S0
+{
+  int f0;
+  int f1;
+  int f2;
+  int f3;
+  int f4;
+  int f5:15;
+  int f6:17;
+  int f7:2;
+  int f8:30;
+} c;
+
+void fn1 ()
+{
+  d = b = 1;
+  for (; b; b = a)
+    {
+      struct S0 e = { 0, 0, 0, 0, 0, 0, 1, 0, 1 };
+      c = e;
+      c.f6 = -1;
+    }
+}
+
+int main ()
+{
+  fn1 ();
+  if (c.f7 != 0)
+    __builtin_abort ();
+  return 0;
+}