New CONST_VECTOR layout

This patch makes CONST_VECTOR use the same encoding as VECTOR_CST.

One problem that occurs in RTL but not at the tree level is that a fair
amount of code uses XVEC and XVECEXP directly on CONST_VECTORs (which is
valid, just with looser checking).  This is complicated by the fact that
vectors are also represented as PARALLELs in some target interfaces,
so using XVECEXP is a good polymorphic way of handling both forms.

Rather than try to untangle all that, the best approach seemed to be to
continue to encode every element in a fixed-length vector.  That way only
target-independent and AArch64 code need to be precise about using
CONST_VECTOR_ELT over XVECEXP.

After this change is no longer valid to modify CONST_VECTORs in-place.
This needed some fix-up in the powerpc backends.

2018-01-02  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	* doc/rtl.texi (const_vector): Describe new encoding scheme.
	* Makefile.in (OBJS): Add rtx-vector-builder.o.
	* rtx-vector-builder.h: New file.
	* rtx-vector-builder.c: Likewise.
	* rtl.h (rtx_def::u2): Add a const_vector field.
	(CONST_VECTOR_NPATTERNS): New macro.
	(CONST_VECTOR_NELTS_PER_PATTERN): Likewise.
	(CONST_VECTOR_DUPLICATE_P): Likewise.
	(CONST_VECTOR_STEPPED_P): Likewise.
	(CONST_VECTOR_ENCODED_ELT): Likewise.
	(const_vec_duplicate_p): Check for a duplicated vector encoding.
	(unwrap_const_vec_duplicate): Likewise.
	(const_vec_series_p): Check for a non-duplicated vector encoding.
	Say that the function only returns true for integer vectors.
	* emit-rtl.c: Include rtx-vector-builder.h.
	(gen_const_vec_duplicate_1): Delete.
	(gen_const_vector): Call gen_const_vec_duplicate instead of
	gen_const_vec_duplicate_1.
	(const_vec_series_p_1): Operate directly on the CONST_VECTOR encoding.
	(gen_const_vec_duplicate): Use rtx_vector_builder.
	(gen_const_vec_series): Likewise.
	(gen_rtx_CONST_VECTOR): Likewise.
	* config/powerpcspe/powerpcspe.c: Include rtx-vector-builder.h.
	(swap_const_vector_halves): Take an rtx pointer rather than rtx.
	Build a new vector rather than modifying a CONST_VECTOR in-place.
	(handle_special_swappables): Update call accordingly.
	* config/rs6000/rs6000-p8swap.c: Include rtx-vector-builder.h.
	(swap_const_vector_halves): Take an rtx pointer rather than rtx.
	Build a new vector rather than modifying a CONST_VECTOR in-place.
	(handle_special_swappables): Update call accordingly.

From-SVN: r256102

1 files changed, 100 insertions, 0 deletions

diff --git a/gcc/rtx-vector-builder.c b/gcc/rtx-vector-builder.c
new file mode 100644
index 0000000..6c39a3d
--- /dev/null
+++ b/gcc/rtx-vector-builder.c
@@ -0,0 +1,100 @@
+/* A class for building vector rtx constants.
+   Copyright (C) 2017 Free Software Foundation, Inc.
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free
+Software Foundation; either version 3, or (at your option) any later
+version.
+
+GCC is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tm.h"
+#include "rtl.h"
+#include "rtx-vector-builder.h"
+
+/* Return a CONST_VECTOR for the current constant.  V is an existing
+   rtvec that contains all the elements.  */
+
+rtx
+rtx_vector_builder::build (rtvec v)
+{
+  finalize ();
+
+  rtx x = find_cached_value ();
+  if (x)
+    return x;
+
+  x = gen_rtx_raw_CONST_VECTOR (m_mode, v);
+  CONST_VECTOR_NPATTERNS (x) = npatterns ();
+  CONST_VECTOR_NELTS_PER_PATTERN (x) = nelts_per_pattern ();
+  return x;
+}
+
+/* Return a vector element with the value BASE + FACTOR * STEP.  */
+
+rtx
+rtx_vector_builder::apply_step (rtx base, unsigned int factor,
+				const wide_int &step) const
+{
+  scalar_int_mode int_mode = as_a <scalar_int_mode> (GET_MODE_INNER (m_mode));
+  return immed_wide_int_const (wi::add (rtx_mode_t (base, int_mode),
+					factor * step),
+			       int_mode);
+}
+
+/* Return a CONST_VECTOR for the current constant.  */
+
+rtx
+rtx_vector_builder::build ()
+{
+  finalize ();
+
+  rtx x = find_cached_value ();
+  if (x)
+    return x;
+
+  unsigned int nelts = GET_MODE_NUNITS (m_mode);
+  rtvec v = rtvec_alloc (nelts);
+  for (unsigned int i = 0; i < nelts; ++i)
+    RTVEC_ELT (v, i) = elt (i);
+  x = gen_rtx_raw_CONST_VECTOR (m_mode, v);
+  CONST_VECTOR_NPATTERNS (x) = npatterns ();
+  CONST_VECTOR_NELTS_PER_PATTERN (x) = nelts_per_pattern ();
+  return x;
+}
+
+/* Check whether there is a global cached value for the vector.
+   Return it if so, otherwise return null.  */
+
+rtx
+rtx_vector_builder::find_cached_value ()
+{
+  if (encoded_nelts () != 1)
+    return NULL_RTX;
+
+  rtx elt = (*this)[0];
+
+  /* We can be called before the global vector constants are set up,
+     but in that case we'll just return null.  */
+  scalar_mode inner_mode = GET_MODE_INNER (m_mode);
+  if (elt == CONST0_RTX (inner_mode))
+    return CONST0_RTX (m_mode);
+  else if (elt == CONST1_RTX (inner_mode))
+    return CONST1_RTX (m_mode);
+  else if (elt == CONSTM1_RTX (inner_mode))
+    return CONSTM1_RTX (m_mode);
+
+  return NULL_RTX;
+}