combine: Fix various shortcomings in make_more_copies (PR87701, PR87780)

This rewrites most of make_more_copies, in the process fixing a few PRs
and some other bugs, and working around a few target problems.  Certain
notes turn out to actually change the meaning of the RTL, so we cannot
drop them; and i386 takes subregs of hard regs.


	PR rtl-optimization/87701
	PR rtl-optimization/87780
	* combine.c (make_more_copies): Rewrite.

From-SVN: r265582

gcc/ChangeLog

+2018-10-29  Segher Boessenkool  <segher@kernel.crashing.org>
+
+	PR rtl-optimization/87701
+	PR rtl-optimization/87780
+	* combine.c (make_more_copies): Rewrite.
+
 2018-10-28  Kugan Vivekanandarajah  <kuganv@linaro.org>
 
 	* doc/generic.texi (ABSU_EXPR): Document.

gcc/combine.c

@@ -14956,25 +14956,20 @@ make_more_copies (void)
 	  rtx set = single_set (insn);
 	  if (!set)
 	    continue;
-	  rtx src = SET_SRC (set);
 	  rtx dest = SET_DEST (set);
 	  if (dest == pc_rtx)
 	    continue;
-	  if (GET_CODE (src) == SUBREG)
-	    src = SUBREG_REG (src);
+	  rtx src = SET_SRC (set);
 	  if (!(REG_P (src) && HARD_REGISTER_P (src)))
 	    continue;
 	  if (TEST_HARD_REG_BIT (fixed_reg_set, REGNO (src)))
 	    continue;
 
 	  rtx new_reg = gen_reg_rtx (GET_MODE (dest));
-	  rtx_insn *insn1 = gen_move_insn (new_reg, src);
-	  rtx_insn *insn2 = gen_move_insn (dest, new_reg);
-	  emit_insn_after (insn1, insn);
-	  emit_insn_after (insn2, insn1);
-	  delete_insn (insn);
-
-	  insn = insn2;
+	  rtx_insn *new_insn = gen_move_insn (new_reg, src);
+	  SET_SRC (set) = new_reg;
+	  emit_insn_before (new_insn, insn);
+	  df_insn_rescan (insn);
 	}
     }
 }