Make CONST_VECTOR_ELT handle implicitly-encoded elements

This patch makes CONST_VECTOR_ELT handle implicitly-encoded elements,
in a similar way to VECTOR_CST_ELT.

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

gcc/
	* rtl.h (CONST_VECTOR_ELT): Redefine to const_vector_elt.
	(const_vector_encoded_nelts): New function.
	(CONST_VECTOR_NUNITS): Redefine to use GET_MODE_NUNITS.
	(const_vector_int_elt, const_vector_elt): Declare.
	* emit-rtl.c (const_vector_int_elt_1): New function.
	(const_vector_elt): Likewise.
	* simplify-rtx.c (simplify_immed_subreg): Avoid taking the address
	of CONST_VECTOR_ELT.

From-SVN: r256104

4 files changed, 82 insertions, 5 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 32396b9..c6d87f4 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,16 @@
 2018-01-02  Richard Sandiford  <richard.sandiford@linaro.org>
 
+	* rtl.h (CONST_VECTOR_ELT): Redefine to const_vector_elt.
+	(const_vector_encoded_nelts): New function.
+	(CONST_VECTOR_NUNITS): Redefine to use GET_MODE_NUNITS.
+	(const_vector_int_elt, const_vector_elt): Declare.
+	* emit-rtl.c (const_vector_int_elt_1): New function.
+	(const_vector_elt): Likewise.
+	* simplify-rtx.c (simplify_immed_subreg): Avoid taking the address
+	of CONST_VECTOR_ELT.
+
+2018-01-02  Richard Sandiford  <richard.sandiford@linaro.org>
+
 	* expr.c: Include rtx-vector-builder.h.
 	(const_vector_mask_from_tree): Use rtx_vector_builder and operate
 	directly on the tree encoding.
diff --git a/gcc/emit-rtl.c b/gcc/emit-rtl.c
index c9599e1..e282b3d 100644
--- a/gcc/emit-rtl.c
+++ b/gcc/emit-rtl.c
@@ -5862,6 +5862,62 @@ init_emit (void)
 #endif
 }
 
+/* Return the value of element I of CONST_VECTOR X as a wide_int.  */
+
+wide_int
+const_vector_int_elt (const_rtx x, unsigned int i)
+{
+  /* First handle elements that are directly encoded.  */
+  machine_mode elt_mode = GET_MODE_INNER (GET_MODE (x));
+  if (i < (unsigned int) XVECLEN (x, 0))
+    return rtx_mode_t (CONST_VECTOR_ENCODED_ELT (x, i), elt_mode);
+
+  /* Identify the pattern that contains element I and work out the index of
+     the last encoded element for that pattern.  */
+  unsigned int encoded_nelts = const_vector_encoded_nelts (x);
+  unsigned int npatterns = CONST_VECTOR_NPATTERNS (x);
+  unsigned int count = i / npatterns;
+  unsigned int pattern = i % npatterns;
+  unsigned int final_i = encoded_nelts - npatterns + pattern;
+
+  /* If there are no steps, the final encoded value is the right one.  */
+  if (!CONST_VECTOR_STEPPED_P (x))
+    return rtx_mode_t (CONST_VECTOR_ENCODED_ELT (x, final_i), elt_mode);
+
+  /* Otherwise work out the value from the last two encoded elements.  */
+  rtx v1 = CONST_VECTOR_ENCODED_ELT (x, final_i - npatterns);
+  rtx v2 = CONST_VECTOR_ENCODED_ELT (x, final_i);
+  wide_int diff = wi::sub (rtx_mode_t (v2, elt_mode),
+			   rtx_mode_t (v1, elt_mode));
+  return wi::add (rtx_mode_t (v2, elt_mode), (count - 2) * diff);
+}
+
+/* Return the value of element I of CONST_VECTOR X.  */
+
+rtx
+const_vector_elt (const_rtx x, unsigned int i)
+{
+  /* First handle elements that are directly encoded.  */
+  if (i < (unsigned int) XVECLEN (x, 0))
+    return CONST_VECTOR_ENCODED_ELT (x, i);
+
+  /* If there are no steps, the final encoded value is the right one.  */
+  if (!CONST_VECTOR_STEPPED_P (x))
+    {
+      /* Identify the pattern that contains element I and work out the index of
+	 the last encoded element for that pattern.  */
+      unsigned int encoded_nelts = const_vector_encoded_nelts (x);
+      unsigned int npatterns = CONST_VECTOR_NPATTERNS (x);
+      unsigned int pattern = i % npatterns;
+      unsigned int final_i = encoded_nelts - npatterns + pattern;
+      return CONST_VECTOR_ENCODED_ELT (x, final_i);
+    }
+
+  /* Otherwise work out the value from the last two encoded elements.  */
+  return immed_wide_int_const (const_vector_int_elt (x, i),
+			       GET_MODE_INNER (GET_MODE (x)));
+}
+
 /* Return true if X is a valid element for a CONST_VECTOR of the given
   mode.  */
 
diff --git a/gcc/rtl.h b/gcc/rtl.h
index 64012d0..ee0ce22 100644
--- a/gcc/rtl.h
+++ b/gcc/rtl.h
@@ -1969,7 +1969,7 @@ set_regno_raw (rtx x, unsigned int regno, unsigned int nregs)
   ((HOST_WIDE_INT) (CONST_FIXED_VALUE (r)->data.low))
 
 /* For a CONST_VECTOR, return element #n.  */
-#define CONST_VECTOR_ELT(RTX, N) XCVECEXP (RTX, 0, N, CONST_VECTOR)
+#define CONST_VECTOR_ELT(RTX, N) const_vector_elt (RTX, N)
 
 /* See rtl.texi for a description of these macros.  */
 #define CONST_VECTOR_NPATTERNS(RTX) \
@@ -1988,8 +1988,16 @@ set_regno_raw (rtx x, unsigned int regno, unsigned int nregs)
 
 #define CONST_VECTOR_ENCODED_ELT(RTX, N) XCVECEXP (RTX, 0, N, CONST_VECTOR)
 
+/* Return the number of elements encoded directly in a CONST_VECTOR.  */
+
+inline unsigned int
+const_vector_encoded_nelts (const_rtx x)
+{
+  return CONST_VECTOR_NPATTERNS (x) * CONST_VECTOR_NELTS_PER_PATTERN (x);
+}
+
 /* For a CONST_VECTOR, return the number of elements in a vector.  */
-#define CONST_VECTOR_NUNITS(RTX) XCVECLEN (RTX, 0, CONST_VECTOR)
+#define CONST_VECTOR_NUNITS(RTX) GET_MODE_NUNITS (GET_MODE (RTX))
 
 /* For a SUBREG rtx, SUBREG_REG extracts the value we want a subreg of.
    SUBREG_BYTE extracts the byte-number.  */
@@ -3001,6 +3009,8 @@ unwrap_const_vec_duplicate (T x)
 }
 
 /* In emit-rtl.c.  */
+extern wide_int const_vector_int_elt (const_rtx, unsigned int);
+extern rtx const_vector_elt (const_rtx, unsigned int);
 extern bool const_vec_series_p_1 (const_rtx, rtx *, rtx *);
 
 /* Return true if X is an integer constant vector that contains a linear
diff --git a/gcc/simplify-rtx.c b/gcc/simplify-rtx.c
index fd6cba7..22cabc5 100644
--- a/gcc/simplify-rtx.c
+++ b/gcc/simplify-rtx.c
@@ -5991,13 +5991,11 @@ simplify_immed_subreg (fixed_size_mode outermode, rtx op,
   if (GET_CODE (op) == CONST_VECTOR)
     {
       num_elem = CONST_VECTOR_NUNITS (op);
-      elems = &CONST_VECTOR_ELT (op, 0);
       elem_bitsize = GET_MODE_UNIT_BITSIZE (innermode);
     }
   else
     {
       num_elem = 1;
-      elems = &op;
       elem_bitsize = max_bitsize;
     }
   /* If this asserts, it is too complicated; reducing value_bit may help.  */
@@ -6008,7 +6006,9 @@ simplify_immed_subreg (fixed_size_mode outermode, rtx op,
   for (elem = 0; elem < num_elem; elem++)
     {
       unsigned char * vp;
-      rtx el = elems[elem];
+      rtx el = (GET_CODE (op) == CONST_VECTOR
+		? CONST_VECTOR_ELT (op, elem)
+		: op);
 
       /* Vectors are kept in target memory order.  (This is probably
 	 a mistake.)  */