[04/nn] Add a VEC_SERIES rtl code

[Richard Sandiford <richard.sandiford@linaro.org>]

This patch adds an rtl representation of a vector linear series
of the form:

  a[I] = BASE + I * STEP

Like vec_duplicate;

- the new rtx can be used for both constant and non-constant vectors
- when used for constant vectors it is wrapped in a (const ...)
- the constant form is only used for variable-length vectors;
  fixed-length vectors still use CONST_VECTOR

At the moment the code is restricted to integer elements, to avoid
concerns over floating-point rounding.


2017-10-23  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* doc/rtl.texi (vec_series): Document.
	(const): Say that the operand can be a vec_series.
	* rtl.def (VEC_SERIES): New rtx code.
	* rtl.h (const_vec_series_p_1): Declare.
	(const_vec_series_p): New function.
	* emit-rtl.h (gen_const_vec_series): Declare.
	(gen_vec_series): Likewise.
	* emit-rtl.c (const_vec_series_p_1, gen_const_vec_series)
	(gen_vec_series): Likewise.
	* optabs.c (expand_mult_highpart): Use gen_const_vec_series.
	* simplify-rtx.c (simplify_unary_operation): Handle negations
	of vector series.
	(simplify_binary_operation_series): New function.
	(simplify_binary_operation_1): Use it.  Handle VEC_SERIES.
	(test_vector_ops_series): New function.
	(test_vector_ops): Call it.
	* config/powerpcspe/altivec.md (altivec_lvsl): Use
	gen_const_vec_series.
	(altivec_lvsr): Likewise.
	* config/rs6000/altivec.md (altivec_lvsl, altivec_lvsr): Likewise.

Index: gcc/doc/rtl.texi
===================================================================
--- gcc/doc/rtl.texi	2017-10-23 11:41:39.185050437 +0100
+++ gcc/doc/rtl.texi	2017-10-23 11:41:41.547050496 +0100
@@ -1677,7 +1677,8 @@ are target-specific and typically repres
 operator.  @var{m} should be a valid address mode.
 
 The second use of @code{const} is to wrap a vector operation.
-In this case @var{exp} must be a @code{vec_duplicate} expression.
+In this case @var{exp} must be a @code{vec_duplicate} or
+@code{vec_series} expression.
 
 @findex high
 @item (high:@var{m} @var{exp})
@@ -2722,6 +2723,10 @@ the same submodes as the input vector mo
 number of output parts must be an integer multiple of the number of input
 parts.
 
+@findex vec_series
+@item (vec_series:@var{m} @var{base} @var{step})
+This operation creates a vector in which element @var{i} is equal to
+@samp{@var{base} + @var{i}*@var{step}}.  @var{m} must be a vector integer mode.
 @end table
 
 @node Conversions
Index: gcc/rtl.def
===================================================================
--- gcc/rtl.def	2017-10-23 11:40:11.378243915 +0100
+++ gcc/rtl.def	2017-10-23 11:41:41.549050496 +0100
@@ -710,6 +710,11 @@ DEF_RTL_EXPR(VEC_CONCAT, "vec_concat", "
    an integer multiple of the number of input parts.  */
 DEF_RTL_EXPR(VEC_DUPLICATE, "vec_duplicate", "e", RTX_UNARY)
 
+/* Creation of a vector in which element I has the value BASE + I * STEP,
+   where BASE is the first operand and STEP is the second.  The result
+   must have a vector integer mode.  */
+DEF_RTL_EXPR(VEC_SERIES, "vec_series", "ee", RTX_BIN_ARITH)
+
 /* Addition with signed saturation */
 DEF_RTL_EXPR(SS_PLUS, "ss_plus", "ee", RTX_COMM_ARITH)
 
Index: gcc/rtl.h
===================================================================
--- gcc/rtl.h	2017-10-23 11:41:39.188050437 +0100
+++ gcc/rtl.h	2017-10-23 11:41:41.549050496 +0100
@@ -2816,6 +2816,51 @@ unwrap_const_vec_duplicate (T x)
   return x;
 }
 
+/* In emit-rtl.c.  */
+extern bool const_vec_series_p_1 (const_rtx, rtx *, rtx *);
+
+/* Return true if X is a constant vector that contains a linear series
+   of the form:
+
+   { B, B + S, B + 2 * S, B + 3 * S, ... }
+
+   for a nonzero S.  Store B and S in *BASE_OUT and *STEP_OUT on sucess.  */
+
+inline bool
+const_vec_series_p (const_rtx x, rtx *base_out, rtx *step_out)
+{
+  if (GET_CODE (x) == CONST_VECTOR
+      && GET_MODE_CLASS (GET_MODE (x)) == MODE_VECTOR_INT)
+    return const_vec_series_p_1 (x, base_out, step_out);
+  if (GET_CODE (x) == CONST && GET_CODE (XEXP (x, 0)) == VEC_SERIES)
+    {
+      *base_out = XEXP (XEXP (x, 0), 0);
+      *step_out = XEXP (XEXP (x, 0), 1);
+      return true;
+    }
+  return false;
+}
+
+/* Return true if X is a vector that contains a linear series of the
+   form:
+
+   { B, B + S, B + 2 * S, B + 3 * S, ... }
+
+   where B and S are constant or nonconstant.  Store B and S in
+   *BASE_OUT and *STEP_OUT on sucess.  */
+
+inline bool
+vec_series_p (const_rtx x, rtx *base_out, rtx *step_out)
+{
+  if (GET_CODE (x) == VEC_SERIES)
+    {
+      *base_out = XEXP (x, 0);
+      *step_out = XEXP (x, 1);
+      return true;
+    }
+  return const_vec_series_p (x, base_out, step_out);
+}
+
 /* Return the unpromoted (outer) mode of SUBREG_PROMOTED_VAR_P subreg X.  */
 
 inline scalar_int_mode
Index: gcc/emit-rtl.h
===================================================================
--- gcc/emit-rtl.h	2017-10-23 11:41:32.369050264 +0100
+++ gcc/emit-rtl.h	2017-10-23 11:41:41.548050496 +0100
@@ -441,6 +441,9 @@ get_max_uid (void)
 extern rtx gen_const_vec_duplicate (machine_mode, rtx);
 extern rtx gen_vec_duplicate (machine_mode, rtx);
 
+extern rtx gen_const_vec_series (machine_mode, rtx, rtx);
+extern rtx gen_vec_series (machine_mode, rtx, rtx);
+
 extern void set_decl_incoming_rtl (tree, rtx, bool);
 
 /* Return a memory reference like MEMREF, but with its mode changed
Index: gcc/emit-rtl.c
===================================================================
--- gcc/emit-rtl.c	2017-10-23 11:41:39.186050437 +0100
+++ gcc/emit-rtl.c	2017-10-23 11:41:41.548050496 +0100
@@ -5796,6 +5796,69 @@ gen_vec_duplicate (machine_mode mode, rt
   return gen_rtx_VEC_DUPLICATE (mode, x);
 }
 
+/* A subroutine of const_vec_series_p that handles the case in which
+   X is known to be an integer CONST_VECTOR.  */
+
+bool
+const_vec_series_p_1 (const_rtx x, rtx *base_out, rtx *step_out)
+{
+  unsigned int nelts = CONST_VECTOR_NUNITS (x);
+  if (nelts < 2)
+    return false;
+
+  scalar_mode inner = GET_MODE_INNER (GET_MODE (x));
+  rtx base = CONST_VECTOR_ELT (x, 0);
+  rtx step = simplify_binary_operation (MINUS, inner,
+					CONST_VECTOR_ELT (x, 1), base);
+  if (rtx_equal_p (step, CONST0_RTX (inner)))
+    return false;
+
+  for (unsigned int i = 2; i < nelts; ++i)
+    {
+      rtx diff = simplify_binary_operation (MINUS, inner,
+					    CONST_VECTOR_ELT (x, i),
+					    CONST_VECTOR_ELT (x, i - 1));
+      if (!rtx_equal_p (step, diff))
+	return false;
+    }
+
+  *base_out = base;
+  *step_out = step;
+  return true;
+}
+
+/* Generate a vector constant of mode MODE in which element I has
+   the value BASE + I * STEP.  */
+
+rtx
+gen_const_vec_series (machine_mode mode, rtx base, rtx step)
+{
+  gcc_assert (CONSTANT_P (base) && CONSTANT_P (step));
+
+  int nunits = GET_MODE_NUNITS (mode);
+  rtvec v = rtvec_alloc (nunits);
+  scalar_mode inner_mode = GET_MODE_INNER (mode);
+  RTVEC_ELT (v, 0) = base;
+  for (int i = 1; i < nunits; ++i)
+    RTVEC_ELT (v, i) = simplify_gen_binary (PLUS, inner_mode,
+					    RTVEC_ELT (v, i - 1), step);
+  return gen_rtx_raw_CONST_VECTOR (mode, v);
+}
+
+/* Generate a vector of mode MODE in which element I has the value
+   BASE + I * STEP.  The result will be a constant if BASE and STEP
+   are both constants.  */
+
+rtx
+gen_vec_series (machine_mode mode, rtx base, rtx step)
+{
+  if (step == const0_rtx)
+    return gen_vec_duplicate (mode, base);
+  if (CONSTANT_P (base) && CONSTANT_P (step))
+    return gen_const_vec_series (mode, base, step);
+  return gen_rtx_VEC_SERIES (mode, base, step);
+}
+
 /* Generate a new vector constant for mode MODE and constant value
    CONSTANT.  */
 
Index: gcc/optabs.c
===================================================================
--- gcc/optabs.c	2017-10-23 11:41:32.369050264 +0100
+++ gcc/optabs.c	2017-10-23 11:41:41.549050496 +0100
@@ -5784,13 +5784,13 @@ expand_mult_highpart (machine_mode mode,
       for (i = 0; i < nunits; ++i)
 	RTVEC_ELT (v, i) = GEN_INT (!BYTES_BIG_ENDIAN + (i & ~1)
 				    + ((i & 1) ? nunits : 0));
+      perm = gen_rtx_CONST_VECTOR (mode, v);
     }
   else
     {
-      for (i = 0; i < nunits; ++i)
-	RTVEC_ELT (v, i) = GEN_INT (2 * i + (BYTES_BIG_ENDIAN ? 0 : 1));
+      int base = BYTES_BIG_ENDIAN ? 0 : 1;
+      perm = gen_const_vec_series (mode, GEN_INT (base), GEN_INT (2));
     }
-  perm = gen_rtx_CONST_VECTOR (mode, v);
 
   return expand_vec_perm (mode, m1, m2, perm, target);
 }
Index: gcc/simplify-rtx.c
===================================================================
--- gcc/simplify-rtx.c	2017-10-23 11:41:36.309050364 +0100
+++ gcc/simplify-rtx.c	2017-10-23 11:41:41.550050496 +0100
@@ -927,7 +927,7 @@ exact_int_to_float_conversion_p (const_r
 simplify_unary_operation_1 (enum rtx_code code, machine_mode mode, rtx op)
 {
   enum rtx_code reversed;
-  rtx temp, elt;
+  rtx temp, elt, base, step;
   scalar_int_mode inner, int_mode, op_mode, op0_mode;
 
   switch (code)
@@ -1185,6 +1185,22 @@ simplify_unary_operation_1 (enum rtx_cod
 	      return simplify_gen_unary (TRUNCATE, int_mode, temp, inner);
 	    }
 	}
+
+      if (vec_series_p (op, &base, &step))
+	{
+	  /* Only create a new series if we can simplify both parts.  In other
+	     cases this isn't really a simplification, and it's not necessarily
+	     a win to replace a vector operation with a scalar operation.  */
+	  scalar_mode inner_mode = GET_MODE_INNER (mode);
+	  base = simplify_unary_operation (NEG, inner_mode, base, inner_mode);
+	  if (base)
+	    {
+	      step = simplify_unary_operation (NEG, inner_mode,
+					       step, inner_mode);
+	      if (step)
+		return gen_vec_series (mode, base, step);
+	    }
+	}
       break;
 
     case TRUNCATE:
@@ -2153,6 +2169,46 @@ simplify_binary_operation (enum rtx_code
   return NULL_RTX;
 }
 
+/* Subroutine of simplify_binary_operation_1 that looks for cases in
+   which OP0 and OP1 are both vector series or vector duplicates
+   (which are really just series with a step of 0).  If so, try to
+   form a new series by applying CODE to the bases and to the steps.
+   Return null if no simplification is possible.
+
+   MODE is the mode of the operation and is known to be a vector
+   integer mode.  */
+
+static rtx
+simplify_binary_operation_series (rtx_code code, machine_mode mode,
+				  rtx op0, rtx op1)
+{
+  rtx base0, step0;
+  if (vec_duplicate_p (op0, &base0))
+    step0 = const0_rtx;
+  else if (!vec_series_p (op0, &base0, &step0))
+    return NULL_RTX;
+
+  rtx base1, step1;
+  if (vec_duplicate_p (op1, &base1))
+    step1 = const0_rtx;
+  else if (!vec_series_p (op1, &base1, &step1))
+    return NULL_RTX;
+
+  /* Only create a new series if we can simplify both parts.  In other
+     cases this isn't really a simplification, and it's not necessarily
+     a win to replace a vector operation with a scalar operation.  */
+  scalar_mode inner_mode = GET_MODE_INNER (mode);
+  rtx new_base = simplify_binary_operation (code, inner_mode, base0, base1);
+  if (!new_base)
+    return NULL_RTX;
+
+  rtx new_step = simplify_binary_operation (code, inner_mode, step0, step1);
+  if (!new_step)
+    return NULL_RTX;
+
+  return gen_vec_series (mode, new_base, new_step);
+}
+
 /* Subroutine of simplify_binary_operation.  Simplify a binary operation
    CODE with result mode MODE, operating on OP0 and OP1.  If OP0 and/or
    OP1 are constant pool references, TRUEOP0 and TRUEOP1 represent the
@@ -2333,6 +2389,14 @@ simplify_binary_operation_1 (enum rtx_co
 	  if (tem)
 	    return tem;
 	}
+
+      /* Handle vector series.  */
+      if (GET_MODE_CLASS (mode) == MODE_VECTOR_INT)
+	{
+	  tem = simplify_binary_operation_series (code, mode, op0, op1);
+	  if (tem)
+	    return tem;
+	}
       break;
 
     case COMPARE:
@@ -2544,6 +2608,14 @@ simplify_binary_operation_1 (enum rtx_co
 	      || plus_minus_operand_p (op1))
 	  && (tem = simplify_plus_minus (code, mode, op0, op1)) != 0)
 	return tem;
+
+      /* Handle vector series.  */
+      if (GET_MODE_CLASS (mode) == MODE_VECTOR_INT)
+	{
+	  tem = simplify_binary_operation_series (code, mode, op0, op1);
+	  if (tem)
+	    return tem;
+	}
       break;
 
     case MULT:
@@ -3495,6 +3567,11 @@ simplify_binary_operation_1 (enum rtx_co
       /* ??? There are simplifications that can be done.  */
       return 0;
 
+    case VEC_SERIES:
+      if (op1 == CONST0_RTX (GET_MODE_INNER (mode)))
+	return gen_vec_duplicate (mode, op0);
+      return 0;
+
     case VEC_SELECT:
       if (!VECTOR_MODE_P (mode))
 	{
@@ -6490,6 +6567,60 @@ test_vector_ops_duplicate (machine_mode
     }
 }
 
+/* Test vector simplifications involving VEC_SERIES in which the
+   operands and result have vector mode MODE.  SCALAR_REG is a pseudo
+   register that holds one element of MODE.  */
+
+static void
+test_vector_ops_series (machine_mode mode, rtx scalar_reg)
+{
+  /* Test unary cases with VEC_SERIES arguments.  */
+  scalar_mode inner_mode = GET_MODE_INNER (mode);
+  rtx duplicate = gen_rtx_VEC_DUPLICATE (mode, scalar_reg);
+  rtx neg_scalar_reg = gen_rtx_NEG (inner_mode, scalar_reg);
+  rtx series_0_r = gen_rtx_VEC_SERIES (mode, const0_rtx, scalar_reg);
+  rtx series_0_nr = gen_rtx_VEC_SERIES (mode, const0_rtx, neg_scalar_reg);
+  rtx series_nr_1 = gen_rtx_VEC_SERIES (mode, neg_scalar_reg, const1_rtx);
+  rtx series_r_m1 = gen_rtx_VEC_SERIES (mode, scalar_reg, constm1_rtx);
+  rtx series_r_r = gen_rtx_VEC_SERIES (mode, scalar_reg, scalar_reg);
+  rtx series_nr_nr = gen_rtx_VEC_SERIES (mode, neg_scalar_reg,
+					 neg_scalar_reg);
+  ASSERT_RTX_EQ (series_0_r,
+		 simplify_unary_operation (NEG, mode, series_0_nr, mode));
+  ASSERT_RTX_EQ (series_r_m1,
+		 simplify_unary_operation (NEG, mode, series_nr_1, mode));
+  ASSERT_RTX_EQ (series_r_r,
+		 simplify_unary_operation (NEG, mode, series_nr_nr, mode));
+
+  /* Test that a VEC_SERIES with a zero step is simplified away.  */
+  ASSERT_RTX_EQ (duplicate,
+		 simplify_binary_operation (VEC_SERIES, mode,
+					    scalar_reg, const0_rtx));
+
+  /* Test PLUS and MINUS with VEC_SERIES.  */
+  rtx series_0_1 = gen_const_vec_series (mode, const0_rtx, const1_rtx);
+  rtx series_0_m1 = gen_const_vec_series (mode, const0_rtx, constm1_rtx);
+  rtx series_r_1 = gen_rtx_VEC_SERIES (mode, scalar_reg, const1_rtx);
+  ASSERT_RTX_EQ (series_r_r,
+		 simplify_binary_operation (PLUS, mode, series_0_r,
+					    duplicate));
+  ASSERT_RTX_EQ (series_r_1,
+		 simplify_binary_operation (PLUS, mode, duplicate,
+					    series_0_1));
+  ASSERT_RTX_EQ (series_r_m1,
+		 simplify_binary_operation (PLUS, mode, duplicate,
+					    series_0_m1));
+  ASSERT_RTX_EQ (series_0_r,
+		 simplify_binary_operation (MINUS, mode, series_r_r,
+					    duplicate));
+  ASSERT_RTX_EQ (series_r_m1,
+		 simplify_binary_operation (MINUS, mode, duplicate,
+					    series_0_1));
+  ASSERT_RTX_EQ (series_r_1,
+		 simplify_binary_operation (MINUS, mode, duplicate,
+					    series_0_m1));
+}
+
 /* Verify some simplifications involving vectors.  */
 
 static void
@@ -6502,6 +6633,9 @@ test_vector_ops ()
 	{
 	  rtx scalar_reg = make_test_reg (GET_MODE_INNER (mode));
 	  test_vector_ops_duplicate (mode, scalar_reg);
+	  if (GET_MODE_CLASS (mode) == MODE_VECTOR_INT
+	      && GET_MODE_NUNITS (mode) > 2)
+	    test_vector_ops_series (mode, scalar_reg);
 	}
     }
 }
Index: gcc/config/powerpcspe/altivec.md
===================================================================
--- gcc/config/powerpcspe/altivec.md	2017-10-23 11:41:32.366050264 +0100
+++ gcc/config/powerpcspe/altivec.md	2017-10-23 11:41:41.546050496 +0100
@@ -2456,13 +2456,10 @@ (define_expand "altivec_lvsl"
     emit_insn (gen_altivec_lvsl_direct (operands[0], operands[1]));
   else
     {
-      int i;
-      rtx mask, perm[16], constv, vperm;
+      rtx mask, constv, vperm;
       mask = gen_reg_rtx (V16QImode);
       emit_insn (gen_altivec_lvsl_direct (mask, operands[1]));
-      for (i = 0; i < 16; ++i)
-        perm[i] = GEN_INT (i);
-      constv = gen_rtx_CONST_VECTOR (V16QImode, gen_rtvec_v (16, perm));
+      constv = gen_const_vec_series (V16QImode, const0_rtx, const1_rtx);
       constv = force_reg (V16QImode, constv);
       vperm = gen_rtx_UNSPEC (V16QImode, gen_rtvec (3, mask, mask, constv),
                               UNSPEC_VPERM);
@@ -2488,13 +2485,10 @@ (define_expand "altivec_lvsr"
     emit_insn (gen_altivec_lvsr_direct (operands[0], operands[1]));
   else
     {
-      int i;
-      rtx mask, perm[16], constv, vperm;
+      rtx mask, constv, vperm;
       mask = gen_reg_rtx (V16QImode);
       emit_insn (gen_altivec_lvsr_direct (mask, operands[1]));
-      for (i = 0; i < 16; ++i)
-        perm[i] = GEN_INT (i);
-      constv = gen_rtx_CONST_VECTOR (V16QImode, gen_rtvec_v (16, perm));
+      constv = gen_const_vec_series (V16QImode, const0_rtx, const1_rtx);
       constv = force_reg (V16QImode, constv);
       vperm = gen_rtx_UNSPEC (V16QImode, gen_rtvec (3, mask, mask, constv),
                               UNSPEC_VPERM);
Index: gcc/config/rs6000/altivec.md
===================================================================
--- gcc/config/rs6000/altivec.md	2017-10-23 11:41:32.366050264 +0100
+++ gcc/config/rs6000/altivec.md	2017-10-23 11:41:41.547050496 +0100
@@ -2573,13 +2573,10 @@ (define_expand "altivec_lvsl"
     emit_insn (gen_altivec_lvsl_direct (operands[0], operands[1]));
   else
     {
-      int i;
-      rtx mask, perm[16], constv, vperm;
+      rtx mask, constv, vperm;
       mask = gen_reg_rtx (V16QImode);
       emit_insn (gen_altivec_lvsl_direct (mask, operands[1]));
-      for (i = 0; i < 16; ++i)
-        perm[i] = GEN_INT (i);
-      constv = gen_rtx_CONST_VECTOR (V16QImode, gen_rtvec_v (16, perm));
+      constv = gen_const_vec_series (V16QImode, const0_rtx, const1_rtx);
       constv = force_reg (V16QImode, constv);
       vperm = gen_rtx_UNSPEC (V16QImode, gen_rtvec (3, mask, mask, constv),
                               UNSPEC_VPERM);
@@ -2614,13 +2611,10 @@ (define_expand "altivec_lvsr"
     emit_insn (gen_altivec_lvsr_direct (operands[0], operands[1]));
   else
     {
-      int i;
-      rtx mask, perm[16], constv, vperm;
+      rtx mask, constv, vperm;
       mask = gen_reg_rtx (V16QImode);
       emit_insn (gen_altivec_lvsr_direct (mask, operands[1]));
-      for (i = 0; i < 16; ++i)
-        perm[i] = GEN_INT (i);
-      constv = gen_rtx_CONST_VECTOR (V16QImode, gen_rtvec_v (16, perm));
+      constv = gen_const_vec_series (V16QImode, const0_rtx, const1_rtx);
       constv = force_reg (V16QImode, constv);
       vperm = gen_rtx_UNSPEC (V16QImode, gen_rtvec (3, mask, mask, constv),
                               UNSPEC_VPERM);