Add QI vector mode support to by-pieces for memset

1. Replace scalar_int_mode with fixed_size_mode in the by-pieces
infrastructure to allow non-integer mode.
2. Rename widest_int_mode_for_size to widest_fixed_size_mode_for_size
to return QI vector mode for memset.
3. Add op_by_pieces_d::smallest_fixed_size_mode_for_size to return the
smallest integer or QI vector mode.
4. Remove clear_by_pieces_1 and use builtin_memset_read_str in
clear_by_pieces to support vector mode broadcast.
5. Add lowpart_subreg_regno, a wrapper around simplify_subreg_regno that
uses subreg_lowpart_offset (mode, prev_mode) as the offset.
6. Add TARGET_GEN_MEMSET_SCRATCH_RTX to allow the backend to use a hard
scratch register to avoid stack realignment when expanding memset.

gcc/

	PR middle-end/90773
	* builtins.c (builtin_memcpy_read_str): Change the mode argument
	from scalar_int_mode to fixed_size_mode.
	(builtin_strncpy_read_str): Likewise.
	(gen_memset_value_from_prev): New function.
	(builtin_memset_read_str): Change the mode argument from
	scalar_int_mode to fixed_size_mode.  Use gen_memset_value_from_prev
	and support CONST_VECTOR.
	(builtin_memset_gen_str): Likewise.
	(try_store_by_multiple_pieces): Use by_pieces_constfn to declare
	constfun.
	* builtins.h (builtin_strncpy_read_str): Replace scalar_int_mode
	with fixed_size_mode.
	(builtin_memset_read_str): Likewise.
	* expr.c (widest_int_mode_for_size): Renamed to ...
	(widest_fixed_size_mode_for_size): Add a bool argument to
	indicate if QI vector mode can be used.
	(by_pieces_ninsns): Call widest_fixed_size_mode_for_size
	instead of widest_int_mode_for_size.
	(pieces_addr::adjust): Change the mode argument from
	scalar_int_mode to fixed_size_mode.
	(op_by_pieces_d): Make m_len read-only.  Add a bool member,
	m_qi_vector_mode, to indicate that QI vector mode can be used.
	(op_by_pieces_d::op_by_pieces_d): Add a bool argument to
	initialize m_qi_vector_mode.  Call widest_fixed_size_mode_for_size
	instead of widest_int_mode_for_size.
	(op_by_pieces_d::get_usable_mode): Change the mode argument from
	scalar_int_mode to fixed_size_mode.  Call
	widest_fixed_size_mode_for_size instead of
	widest_int_mode_for_size.
	(op_by_pieces_d::smallest_fixed_size_mode_for_size): New member
	function to return the smallest integer or QI vector mode.
	(op_by_pieces_d::run): Call widest_fixed_size_mode_for_size
	instead of widest_int_mode_for_size.  Call
	smallest_fixed_size_mode_for_size instead of
	smallest_int_mode_for_size.
	(store_by_pieces_d::store_by_pieces_d): Add a bool argument to
	indicate that QI vector mode can be used and pass it to
	op_by_pieces_d::op_by_pieces_d.
	(can_store_by_pieces): Call widest_fixed_size_mode_for_size
	instead of widest_int_mode_for_size.  Pass memsetp to
	widest_fixed_size_mode_for_size to support QI vector mode.
	Allow all CONST_VECTORs for memset if vec_duplicate is supported.
	(store_by_pieces): Pass memsetp to
	store_by_pieces_d::store_by_pieces_d.
	(clear_by_pieces_1): Removed.
	(clear_by_pieces): Replace clear_by_pieces_1 with
	builtin_memset_read_str and pass true to store_by_pieces_d to
	support vector mode broadcast.
	(string_cst_read_str): Change the mode argument from
	scalar_int_mode to fixed_size_mode.
	* expr.h (by_pieces_constfn): Change scalar_int_mode to
	fixed_size_mode.
	(by_pieces_prev): Likewise.
	* rtl.h (lowpart_subreg_regno): New.
	* rtlanal.c (lowpart_subreg_regno): New.  A wrapper around
	simplify_subreg_regno.
	* target.def (gen_memset_scratch_rtx): New hook.
	* doc/tm.texi.in: Add TARGET_GEN_MEMSET_SCRATCH_RTX.
	* doc/tm.texi: Regenerated.

gcc/testsuite/

	* gcc.target/i386/pr100865-3.c: Expect vmovdqu8 instead of
	vmovdqu.
	* gcc.target/i386/pr100865-4b.c: Likewise.

2 files changed, 9 insertions, 0 deletions

diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index a464d26..cb01528 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -12158,6 +12158,13 @@ This function prepares to emit a conditional comparison within a sequence
  @var{bit_code} is @code{AND} or @code{IOR}, which is the op on the compares.
 @end deftypefn
 
+@deftypefn {Target Hook} rtx TARGET_GEN_MEMSET_SCRATCH_RTX (machine_mode @var{mode})
+This hook should return an rtx for a scratch register in @var{mode} to
+be used when expanding memset calls.  The backend can use a hard scratch
+register to avoid stack realignment when expanding memset.  The default
+is @code{gen_reg_rtx}.
+@end deftypefn
+
 @deftypefn {Target Hook} unsigned TARGET_LOOP_UNROLL_ADJUST (unsigned @var{nunroll}, class loop *@var{loop})
 This target hook returns a new value for the number of times @var{loop}
 should be unrolled. The parameter @var{nunroll} is the number of times
diff --git a/gcc/doc/tm.texi.in b/gcc/doc/tm.texi.in
index 0b60342..4a522ae 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -7986,6 +7986,8 @@ lists.
 
 @hook TARGET_GEN_CCMP_NEXT
 
+@hook TARGET_GEN_MEMSET_SCRATCH_RTX
+
 @hook TARGET_LOOP_UNROLL_ADJUST
 
 @defmac POWI_MAX_MULTS