>> +const unsigned int SRP_POINTER  = -1;
>> +const unsigned int SRP_SIGNED   = 0;
>> +const unsigned int SRP_UNSIGNED = 1;
>> +const unsigned int SRP_SIGNED_AND_UNSIGNED = 2;
> 
> But most importantly, I thought Richard Henderson suggested
> to use SRP_POINTER 0, SRP_SIGNED 1, SRP_UNSIGNED 2, SRP_SIGNED_AND_UNSIGNED 3,
> that way when checking e.g. SUBREG_PROMOTED_SIGNED_P or
> SUBREG_PROMOTED_UNSIGNED_P you can check just the single bit.
> Where something tested for SUBREG_PROMOTED_UNSIGNED_P () == -1 just
> use SUBREG_PROMOTED_GET.

The problem with SRP_POINTER 0, SRP_SIGNED 1, SRP_UNSIGNED 2,
SRP_SIGNED_AND_UNSIGNED 3 (as I understand) is that, it will be
incompatible with TYPE_UNSIGNED (tree) and defines of
POINTER_EXTEND_UNSIGNED values. We will have to then translate while
setting to SRP_* values . Also SUBREG_PROMOTED_SIGNED_P is now checked
in some cases for != 0 (meaning SRP_POINTER or SRP_UNSIGNED) and in some
cases > 0 (meaning SRP_UNSIGNED).

Since our aim is to perform single bit checks, why don’t we just use
this representation internally (i.e.  _rtx->unchanging = 1 if SRP_SIGNED
and _rtx->volatil = 1 if SRP_UNSIGNED). As for SUBREG_PROMOTED_SIGNED_P,
we still have to return -1 or 1 depending on SRP_POINTER or SRP_UNSIGNED.


const unsigned int SRP_POINTER	= -1;
const unsigned int SRP_SIGNED   = 0;
const unsigned int SRP_UNSIGNED = 1;
const unsigned int SRP_SIGNED_AND_UNSIGNED = 2;

/* Sets promoted mode for SUBREG_PROMOTED_VAR_P(), */
#define SUBREG_PROMOTED_SET(RTX, VAL)	                        \
do {							        \
  rtx const _rtx = RTL_FLAG_CHECK1 ("SUBREG_PROMOTED_SET",	\
                                    (RTX), SUBREG);		\
  switch ((VAL))						\
  {								\
    case SRP_POINTER:						\
      _rtx->volatil = 0;					\
      _rtx->unchanging = 0;					\
      break;							\
    case SRP_SIGNED:						\
      _rtx->volatil = 0;					\
      _rtx->unchanging = 1;					\
      break;							\
    case SRP_UNSIGNED:						\
      _rtx->volatil = 1;					\
      _rtx->unchanging = 0;					\
      break;							\
    case SRP_SIGNED_AND_UNSIGNED:				\
      _rtx->volatil = 1;					\
      _rtx->unchanging = 1;					\
      break;							\
  }								\
} while (0)

/* Gets promoted mode for SUBREG_PROMOTED_VAR_P(). */
#define SUBREG_PROMOTED_GET(RTX)	\
  (2 * (RTL_FLAG_CHECK1 ("SUBREG_PROMOTED_GET", (RTX), SUBREG)->volatil)\
   + (RTX)->unchanging - 1)

/* Predicate to check if RTX of SUBREG_PROMOTED_VAR_P() is promoted
   for SIGNED type.  */
#define SUBREG_PROMOTED_SIGNED_P(RTX)	\
  (RTL_FLAG_CHECK1 ("SUBREG_PROMOTED_SIGNED_P", (RTX),
SUBREG)->unchanging == 1)

/* Predicate to check if RTX of SUBREG_PROMOTED_VAR_P() is promoted
   for UNSIGNED type.  In case of SRP_POINTER, SUBREG_PROMOTED_UNSIGNED_P
   returns -1 as this is in most cases handled like unsigned extension,
   except for generating instructions where special code is emitted for
   (ptr_extend insns) on some architectures.  */
   #define SUBREG_PROMOTED_UNSIGNED_P(RTX)	\
  ((((RTL_FLAG_CHECK1 ("SUBREG_PROMOTED_UNSIGNED_P", (RTX),
SUBREG)->volatil)\
     + (RTX)->unchanging) == 0) ? -1 : ((RTX)->volatil == 1))

Am I missing anything here? Please let me know. I am attaching the patch
based on this with your other review comments addressed.

Thanks,
Kugan

gcc/
2014-06-25  Kugan Vivekanandarajah  <kuganv@linaro.org>

	* calls.c (precompute_arguments): Use new SUBREG_PROMOTED_SET
	instead of SUBREG_PROMOTED_UNSIGNED_SET
	(expand_call): Likewise.
	* expr.c (convert_move): Use new SUBREG_CHECK_PROMOTED_SIGN
	instead of SUBREG_PROMOTED_UNSIGNED_P.
	(convert_modes): Likewise.
	(store_expr): Likewise.
	(expand_expr_real_1): Use new SUBREG_PROMOTED_SET
	instead of SUBREG_PROMOTED_UNSIGNED_SET.
	* function.c (assign_param_setup_reg): Use new SUBREG_PROMOTED_SET
	instead of SUBREG_PROMOTED_UNSIGNED_SET.
	* ifcvt.c (noce_emit_cmove): Updated to use
	SUBREG_PROMOTED_UNSIGNED_P and SUBREG_PROMOTED_SIGNED_P.
	* internal-fn.c (ubsan_expand_si_overflow_mul_check): Use
	SUBREG_PROMOTED_SET instead of SUBREG_PROMOTED_UNSIGNED_SET.
	* optabs.c (widen_operand): Use new SUBREG_CHECK_PROMOTED_SIGN
	instead of SUBREG_PROMOTED_UNSIGNED_P.
	* rtl.h (SUBREG_PROMOTED_UNSIGNED_SET): Remove.
	(SUBREG_PROMOTED_SET): New define.
	(SUBREG_PROMOTED_GET): Likewise.
	(SUBREG_PROMOTED_SIGNED_P): Likewise.
	(SUBREG_CHECK_PROMOTED_SIGN): Likewise.
	(SUBREG_PROMOTED_UNSIGNED_P): Updated.
	* rtlanal.c (simplify_unary_operation_1): Use new
	SUBREG_PROMOTED_SET instead of SUBREG_PROMOTED_UNSIGNED_SET.
	* simplify-rtx.c (simplify_unary_operation_1): Use new
	SUBREG_PROMOTED_SIGNED_P instead of
	!SUBREG_PROMOTED_UNSIGNED_P.
	(simplify_subreg): Use new SUBREG_PROMOTED_SET instead of
	 SUBREG_PROMOTED_UNSIGNED_SET.