[PATCH 011/236] Replace PREV_INSN et al macros with functions

[David Malcolm <dmalcolm at redhat dot com>]

Yet more scaffolding: convert the NEXT_INSN/PREV_INSN macros
and their SET_* variants into functions.

Convert the rvalue-style functions into returning
rtx_insn * rather than plain rtx.

For now, this is done by adding a checked cast, but I hope this can
eventually become a field lookup.  The lvalue forms for now return an rtx&
to allow in-place modification.

gcc/
	* rtl.h (PREV_INSN): Convert to an inline function.  Strengthen
	the return type from rtx to rtx_insn *,  which will enable various
	conversions in followup patches.  For now this is is done by a
	checked cast.
	(NEXT_INSN): Likewise.
	(SET_PREV_INSN): Convert to an inilne function.  This is intended
	for use as an lvalue, and so returns an rtx& to allow in-place
	modification.
	(SET_NEXT_INSN): Likewise.
---
 gcc/rtl.h | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/gcc/rtl.h b/gcc/rtl.h
index e08f05b..5936829 100644
--- a/gcc/rtl.h
+++ b/gcc/rtl.h
@@ -972,15 +972,33 @@ extern void rtl_check_failed_flag (const char *, const_rtx, const char *,
   (RTL_INSN_CHAIN_FLAG_CHECK ("INSN_UID", (INSN))->u2.insn_uid)
 
 /* Chain insns together in sequence.  */
+
 /* For now these are split in two: an rvalue form:
      PREV_INSN/NEXT_INSN
    and an lvalue form:
      SET_NEXT_INSN/SET_PREV_INSN.  */
 
-#define PREV_INSN(INSN)      XEXP ((const_rtx)(INSN), 0)
-#define SET_PREV_INSN(INSN)  XEXP (INSN, 0)
-#define NEXT_INSN(INSN)      XEXP ((const_rtx)(INSN), 1)
-#define SET_NEXT_INSN(INSN)  XEXP (INSN, 1)
+inline rtx_insn *PREV_INSN (const_rtx insn)
+{
+  rtx prev = XEXP (insn, 0);
+  return as_a_nullable <rtx_insn *> (prev);
+}
+
+inline rtx& SET_PREV_INSN (rtx insn)
+{
+  return XEXP (insn, 0);
+}
+
+inline rtx_insn *NEXT_INSN (const_rtx insn)
+{
+  rtx next = XEXP (insn, 1);
+  return as_a_nullable <rtx_insn *> (next);
+}
+
+inline rtx& SET_NEXT_INSN (rtx insn)
+{
+  return XEXP (insn, 1);
+}
 
 #define BLOCK_FOR_INSN(INSN) XBBDEF (INSN, 2)
 
-- 
1.8.5.3