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Re: [4/9] Add a dedicated rtx union member for REGs

On 05/18/2015 12:19 PM, Richard Sandiford wrote:
This patch replaces the current REG "i0" format with a dedicated structure,
so that we can make use of the extra 32 bits in the "i" field.

Of the places that iterate on formats and do something for 'i's,
most already handled REGs specially before the format walk and
so don't need to check for 'r'.  Otherwise it's mostly just a case
of adding dummy 'r' cases in order avoid the default gcc_unreachable ()
(in cases where we do the same for 'i').  The main exceptions are the
cselib.c and lra-constraints.c changes.

final.c:leaf_renumber_regs_insn handled REGs specially but then
went on to do a no-op walk of the format.  I just added an early
exit instead of an empty 'r' case.

	* rtl.def (REG): Change format to "r".
	* rtl.h (rtunion): Remove rt_reg.
	(reg_info): New structure.
	(rtx_def): Add reg field to main union.
	(X0REGATTR): Delete.
	(REG_CHECK): New macro.
	(SET_REGNO_RAW, rhs_regno, REG_ATTRS): Use it.
	* rtl.c (rtx_format): Document "r".
	(rtx_code_size): Handle REG specially.
	* gengenrtl.c (special_format): Return true for formats
	that include 'r'.
	* gengtype.c (adjust_field_rtx_def): Handle 'r' fields.
	Deal with REG_ATTRS after the field loop.
	* emit-rtl.c (gen_raw_REG): Call rtx_alloc_stat directly.
	* expmed.c (init_expmed): Call gen_raw_REG instead of
	* expr.c (init_expr_target): Likewise.
	* regcprop.c (maybe_mode_change): Likewise.
	* varasm.c (make_decl_rtl): Likewise.
	* final.c (leaf_renumber_regs_insn): Return early after
	handling REGs.
	* genemit.c (gen_exp): Handle 'r' fields.
	* genpeep.c (match_rtx): Likewise.
	* gensupport.c (subst_pattern_match): Likewise.
	(get_alternatives_number, collect_insn_data, alter_predicate_for_insn)
	(alter_constraints, subst_dup): Likewise.
	* read-rtl.c (read_rtx_code): Likewise.
	* print-rtl.c (print_rtx): Likewise.
	* genrecog.c (find_operand, find_matching_operand): Likewise.
	(validate_pattern, match_pattern_2): Likewise.
	(parameter::UINT, rtx_test::REGNO_FIELD): New enum values.
	(rtx_test::regno_field): New function.
	(operator ==, safe_to_hoist_p, transition_parameter_type)
	(parameter_type_string, print_parameter_value)
	(print_nonbool_test, print_test): Handle new enum values.
	* cselib.c (rtx_equal_for_cselib_1): Handle REG specially.
	* lra-constraints.c (operands_match_p): Likewise.
Just to confirm, this doesn't change the size of a REG object, right? If it doesn't change the size, then it's OK.

If we make REG objects larger, we potentially increase the amount of memory used by GCC.

If we make REG objects smaller, then we run the risk of memory overwrites when reload changes REG objects into MEM objects.

The former is bad, the latter is a disaster waiting to happen.


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