On Wed, May 26, 2021 at 10:28:16AM +0200, Richard Biener wrote:
> > > >
> > > >  -- Target Hook: rtx TARGET_GEN_MEMSET_VALUE (rtx DATA, scalar_int_mode
> > > >           MODE)
> > > >      This function returns the RTL of a register containing
> > > >      'GET_MODE_SIZE (MODE)' consecutive copies of the unsigned char
> > > >      value given in the RTL register DATA.  For example, if MODE is 4
> > > >      bytes wide, return the RTL for 0x01010101*DATA.
> > >
> > > For this one I wonder if it should be an optab instead.  Couldn't you
> > > use the existing vec_duplicate for this by using (paradoxical) subregs
> > > like (subreg:TI (vec_duplicate:VnQI (subreg:VnQI (reg:QI ...)))?
> >
> > I tried.   It doesn't even work on x86.  See:
> >
> > https://gcc.gnu.org/pipermail/gcc-patches/2021-May/570661.html
> 
> Not sure what I should read from there...
> 
> > There are special cases to subreg HI, SI and DI modes of TI mode in
> > ix86_gen_memset_value_from_prev.   simplify_gen_subreg doesn't
> > work here.   Each backend may need its own special handling.
> 
> OK, I guess I'm not (RTL) qualified enough to further review these parts,
> sorry.  Since we're doing code generation the canonical way to communicate
> with backends should be optabs, not some set of disconnected target hooks.
> But as said, I probably don't know enough of RTL to see why it's the only way.
> 
> Richard.

Here is the patch to add optabs instead.  Does it look OK?

Thanks.

H.J.
---
Add 2 optabs:

1. integer_extract: Extract lower bit value from the integer value in
TImode, OImode or XImode.
2. vec_const_duplicate: Broadcast a QImode constant to a vector.  It is
similar to vec_duplicate.  Since the resulting vector is computable at
compile-time, vec_duplicate may not be faster and backend can opt out
broadcasting from a constant while opting in broadcasting from a
variable.

and rewrite builtin_memset_read_str/builtin_memset_gen_str to support
target instructions to duplicate QImode value to TImode, OImode or XImode
value for memmset.

Add TARGET_GEN_MEMSET_SCRATCH_RTX to allow the backend to use a hard
scratch register to avoid stack realignment when expanding memset.

        PR middle-end/90773
        * builtins.c (gen_memset_value_from_prev): New function.
        (gen_memset_broadcast): Likewise.
        (builtin_memset_read_str): Use gen_memset_value_from_prev
        and gen_memset_broadcast.
        (builtin_memset_gen_str): Likewise.
        * optabs.def: Add integer_extract and vec_const_duplicate.
        * target.def (gen_memset_scratch_rtx): New hook.
        * doc/md.texi: Document vec_const_duplicate and integer_extract.
        * doc/tm.texi.in: Add TARGET_GEN_MEMSET_SCRATCH_RTX.
        * doc/tm.texi: Regenerated.
---
 gcc/builtins.c     | 117 +++++++++++++++++++++++++++++++++++++--------
 gcc/doc/md.texi    |  16 +++++++
 gcc/doc/tm.texi    |   5 ++
 gcc/doc/tm.texi.in |   2 +
 gcc/optabs.def     |   4 ++
 gcc/target.def     |   7 +++
 6 files changed, 131 insertions(+), 20 deletions(-)

diff --git a/gcc/builtins.c b/gcc/builtins.c
index af1fe49bb48..7683169eb96 100644
--- a/gcc/builtins.c
+++ b/gcc/builtins.c
@@ -6598,26 +6598,106 @@ expand_builtin_strncpy (tree exp, rtx target)
   return NULL_RTX;
 }
 
+/* Return the RTL of a register in MODE generated from PREV in the
+   previous iteration.  */
+
+static rtx
+gen_memset_value_from_prev (void *prevp, scalar_int_mode mode)
+{
+  rtx target = nullptr;
+  by_pieces_prev *prev = (by_pieces_prev *) prevp;
+  if (prev != nullptr && prev->data != nullptr)
+    {
+      /* Use the previous data in the same mode.  */
+      if (prev->mode == mode)
+       return prev->data;
+
+      /* Extract the RTL in MODE from PREV.  */
+      enum insn_code icode
+       = convert_optab_handler (integer_extract_optab, mode,
+                                prev->mode);
+      if (icode != CODE_FOR_nothing)
+       {
+         target = gen_reg_rtx (mode);
+         class expand_operand ops[2];
+         create_output_operand (&ops[0], target, mode);
+         create_input_operand (&ops[1], prev->data, prev->mode);
+         expand_insn (icode, 2, ops);
+         if (!rtx_equal_p (target, ops[0].value))
+           emit_move_insn (target, ops[0].value);
+       }
+      else
+       target = simplify_gen_subreg (mode, prev->data, prev->mode, 0);
+    }
+  return target;
+}
+
+/* Return the RTL of a register in MODE broadcasted from DATA.  */
+
+static rtx
+gen_memset_broadcast (enum optab_tag broadcast_optab, rtx data,
+                     scalar_int_mode mode)
+{
+  /* Skip if regno_reg_rtx isn't initialized.  */
+  if (!regno_reg_rtx)
+    return nullptr;
+
+  rtx target = nullptr;
+
+  unsigned int nunits = GET_MODE_SIZE (mode) / GET_MODE_SIZE (QImode);
+  machine_mode vector_mode;
+  if (!mode_for_vector (QImode, nunits).exists (&vector_mode))
+    gcc_unreachable ();
+
+  enum insn_code icode = optab_handler (broadcast_optab, vector_mode);
+  if (icode != CODE_FOR_nothing)
+    {
+      target = targetm.gen_memset_scratch_rtx (vector_mode);
+      class expand_operand ops[2];
+      create_output_operand (&ops[0], target, vector_mode);
+      create_input_operand (&ops[1], (rtx) data, QImode);
+      expand_insn (icode, 2, ops);
+      if (!rtx_equal_p (target, ops[0].value))
+       emit_move_insn (target, ops[0].value);
+      if (REGNO (target) < FIRST_PSEUDO_REGISTER)
+       target = gen_rtx_REG (mode, REGNO (target));
+      else
+       target = convert_to_mode (mode, target, 1);
+    }
+
+  return target;
+}
+
 /* Callback routine for store_by_pieces.  Read GET_MODE_BITSIZE (MODE)
    bytes from constant string DATA + OFFSET and return it as target
    constant.  If PREV isn't nullptr, it has the RTL info from the
    previous iteration.  */
 
 rtx
-builtin_memset_read_str (void *data, void *prevp,
+builtin_memset_read_str (void *data, void *prev,
                         HOST_WIDE_INT offset ATTRIBUTE_UNUSED,
                         scalar_int_mode mode)
 {
-  by_pieces_prev *prev = (by_pieces_prev *) prevp;
-  if (prev != nullptr && prev->data != nullptr)
+  rtx target;
+
+  /* Don't use the previous value if size is 1.  */
+  if (GET_MODE_SIZE (mode) != 1)
     {
-      /* Use the previous data in the same mode.  */
-      if (prev->mode == mode)
-       return prev->data;
+      target = gen_memset_value_from_prev (prev, mode);
+      if (target != nullptr)
+       return target;
     }
 
   const char *c = (const char *) data;
-  char *p = XALLOCAVEC (char, GET_MODE_SIZE (mode));
+  char *p = XALLOCAVEC (char, GET_MODE_SIZE (QImode));
+  memset (p, *c, GET_MODE_SIZE (QImode));
+  rtx src = c_readstr (p, QImode);
+  target = gen_memset_broadcast (vec_const_duplicate_optab, src,
+                                mode);
+  if (target != nullptr)
+    return target;
+
+  p = XALLOCAVEC (char, GET_MODE_SIZE (mode));
 
   memset (p, *c, GET_MODE_SIZE (mode));
 
@@ -6631,7 +6711,7 @@ builtin_memset_read_str (void *data, void *prevp,
    nullptr, it has the RTL info from the previous iteration.  */
 
 static rtx
-builtin_memset_gen_str (void *data, void *prevp,
+builtin_memset_gen_str (void *data, void *prev,
                        HOST_WIDE_INT offset ATTRIBUTE_UNUSED,
                        scalar_int_mode mode)
 {
@@ -6639,22 +6719,19 @@ builtin_memset_gen_str (void *data, void *prevp,
   size_t size;
   char *p;
 
-  by_pieces_prev *prev = (by_pieces_prev *) prevp;
-  if (prev != nullptr && prev->data != nullptr)
-    {
-      /* Use the previous data in the same mode.  */
-      if (prev->mode == mode)
-       return prev->data;
-
-      target = simplify_gen_subreg (mode, prev->data, prev->mode, 0);
-      if (target != nullptr)
-       return target;
-    }
-
   size = GET_MODE_SIZE (mode);
   if (size == 1)
     return (rtx) data;
 
+  target = gen_memset_value_from_prev (prev, mode);
+  if (target != nullptr)
+    return target;
+
+  target = gen_memset_broadcast (vec_duplicate_optab, (rtx) data,
+                                mode);
+  if (target != nullptr)
+    return target;
+
   p = XALLOCAVEC (char, size);
   memset (p, 1, size);
   coeff = c_readstr (p, mode);
diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi
index 00caf3844cc..a798fb1a97e 100644
--- a/gcc/doc/md.texi
+++ b/gcc/doc/md.texi
@@ -5079,6 +5079,16 @@ vectors go through the @code{mov@var{m}} pattern instead.
 
 This pattern is not allowed to @code{FAIL}.
 
+@cindex @code{vec_const_duplicate@var{m}} instruction pattern
+@item @samp{vec_const_duplicate@var{m}}
+Initialize vector output operand 0 in mode @var{m} so that each element
+has the value given by constant input operand 1.
+
+This pattern only handles duplicates of constant inputs.  Non-constant
+vectors go through the @code{vec_duplicate@var{m}} pattern instead.
+
+This pattern is not allowed to @code{FAIL}.
+
 @cindex @code{vec_series@var{m}} instruction pattern
 @item @samp{vec_series@var{m}}
 Initialize vector output operand 0 so that element @var{i} is equal to
@@ -7904,6 +7914,12 @@ inclusive and operand 1 exclusive.
 If this pattern is not defined, a call to the library function
 @code{__clear_cache} is used.
 
+@cindex @code{integer_extract@var{m}@var{n}} instruction pattern
+@item @samp{integer_extract@var{m}@var{n}}
+Extract lower bit value from the integer value in @code{TImode},
+@code{OImode} or @code{XImode}.  Operand 1 is the integer in mode
+@var{n} and operand 0 stores value to be extracted in mode @var{m}.
+
 @end table
 
 @end ifset
diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index e3a080e4a7c..8ccc262b1fc 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -11894,6 +11894,11 @@ 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 scratch register in @var{mode} to
+be used by memset broadcast.  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 d9fbbe20e6f..99bf01fe25d 100644
--- a/gcc/doc/tm.texi.in
+++ b/gcc/doc/tm.texi.in
@@ -7960,6 +7960,8 @@ lists.
 
 @hook TARGET_GEN_CCMP_NEXT
 
+@hook TARGET_GEN_MEMSET_SCRATCH_RTX
+
 @hook TARGET_LOOP_UNROLL_ADJUST
 
 @defmac POWI_MAX_MULTS
diff --git a/gcc/optabs.def b/gcc/optabs.def
index b192a9d070b..fd8ab8b4a26 100644
--- a/gcc/optabs.def
+++ b/gcc/optabs.def
@@ -100,6 +100,8 @@ OPTAB_CD(vec_init_optab, "vec_init$a$b")
 
 OPTAB_CD (while_ult_optab, "while_ult$a$b")
 
+OPTAB_CD (integer_extract_optab, "integer_extract$a$b")
+
 OPTAB_NL(add_optab, "add$P$a3", PLUS, "add", '3', gen_int_fp_fixed_libfunc)
 OPTAB_NX(add_optab, "add$F$a3")
 OPTAB_NX(add_optab, "add$Q$a3")
@@ -453,3 +455,5 @@ OPTAB_DC (vec_series_optab, "vec_series$a", VEC_SERIES)
 OPTAB_D (vec_shl_insert_optab, "vec_shl_insert_$a")
 OPTAB_D (len_load_optab, "len_load_$a")
 OPTAB_D (len_store_optab, "len_store_$a")
+
+OPTAB_DC (vec_const_duplicate_optab, "vec_const_duplicate$a", VEC_DUPLICATE)
diff --git a/gcc/target.def b/gcc/target.def
index 1dffedc81e4..b89e7c24471 100644
--- a/gcc/target.def
+++ b/gcc/target.def
@@ -2724,6 +2724,13 @@ DEFHOOK
  rtx, (rtx_insn **prep_seq, rtx_insn **gen_seq, rtx prev, int cmp_code, tree 
op0, tree op1, int bit_code),
  NULL)
 
+DEFHOOK
+(gen_memset_scratch_rtx,
+ "This hook should return an rtx for scratch register in @var{mode} to\n\
+be used by memset broadcast.  The default is @code{gen_reg_rtx}.",
+ rtx, (machine_mode mode),
+ gen_reg_rtx)
+
 /* Return a new value for loop unroll size.  */
 DEFHOOK
 (loop_unroll_adjust,
-- 
2.31.1

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