combine: Fix problem with RTL checking

As Jakub found, after my recent combine patch at least on x86 problems
show up with RTL checking enabled.  This is because the I2 generated
by a successful instruction combination can write not only a register
but it can also write a paradoxical subreg of one.

This fixes it.


	* combine.c (try_combine): When adjusting LOG_LINKS for the destination
	that moved to I2, also allow destinations that are a paradoxical
	subreg (instead of a normal reg).

From-SVN: r257736

gcc/ChangeLog

+2018-02-16  Segher Boessenkool  <segher@kernel.crashing.org>
+
+	* combine.c (try_combine): When adjusting LOG_LINKS for the destination
+	that moved to I2, also allow destinations that are a paradoxical
+	subreg (instead of a normal reg).
+
 2018-02-16  Oleg Endo  <olegendo@gcc.gnu.org>
 
 	PR target/83831

gcc/combine.c

@@ -4283,7 +4283,12 @@ try_combine (rtx_insn *i3, rtx_insn *i2, rtx_insn *i1, rtx_insn *i0,
       if (GET_CODE (x) == PARALLEL)
 	x = XVECEXP (newi2pat, 0, 0);
 
-      unsigned int regno = REGNO (SET_DEST (x));
+      /* It can only be a SET of a REG or of a paradoxical SUBREG of a REG.  */
+      x = SET_DEST (x);
+      if (paradoxical_subreg_p (x))
+	x = SUBREG_REG (x);
+
+      unsigned int regno = REGNO (x);
 
       bool done = false;
       for (rtx_insn *insn = NEXT_INSN (i3);