re PR tree-optimization/56064 (Optimize VIEW_CONVERT_EXPR with FIXED_CST)

gcc/
	PR tree-optimization/56064
	* fixed-value.c (fixed_from_double_int): New function.
	* fixed-value.h (fixed_from_double_int): New prototype.
	(const_fixed_from_double_int): New static inline function.
	* fold-const.c (native_interpret_fixed): New static function.
	(native_interpret_expr) <FIXED_POINT_TYPE>: Use it.
	(can_native_interpret_type_p) <FIXED_POINT_TYPE>: Return true.
	(native_encode_fixed): New static function.
	(native_encode_expr) <FIXED_CST>: Use it.
	(native_interpret_int): Move double_int worker code to...
	* double-int.c (double_int::from_buffer): ...this new static method.
	* double-int.h (double_int::from_buffer): Prototype it.

gcc/testsuite/
	PR tree-optimization/56064
	* gcc.dg/fixed-point/view-convert.c: New test.

From-SVN: r195574

1 files changed, 48 insertions, 0 deletions

diff --git a/gcc/double-int.c b/gcc/double-int.c
index a02a6aa..918ce22 100644
--- a/gcc/double-int.c
+++ b/gcc/double-int.c
@@ -641,6 +641,54 @@ div_and_round_double (unsigned code, int uns,
   return overflow;
 }
 
+
+/* Construct from a buffer of length LEN.  BUFFER will be read according
+   to byte endianess and word endianess.  Only the lower LEN bytes
+   of the result are set; the remaining high bytes are cleared.  */
+
+double_int
+double_int::from_buffer (const unsigned char *buffer, int len)
+{
+  double_int result = double_int_zero;
+  int words = len / UNITS_PER_WORD;
+
+  gcc_assert (len * BITS_PER_UNIT <= HOST_BITS_PER_DOUBLE_INT);
+
+  for (int byte = 0; byte < len; byte++)
+    {
+      int offset;
+      int bitpos = byte * BITS_PER_UNIT;
+      unsigned HOST_WIDE_INT value;
+
+      if (len > UNITS_PER_WORD)
+	{
+	  int word = byte / UNITS_PER_WORD;
+
+	  if (WORDS_BIG_ENDIAN)
+	    word = (words - 1) - word;
+
+	  offset = word * UNITS_PER_WORD;
+
+	  if (BYTES_BIG_ENDIAN)
+	    offset += (UNITS_PER_WORD - 1) - (byte % UNITS_PER_WORD);
+	  else
+	    offset += byte % UNITS_PER_WORD;
+	}
+      else
+	offset = BYTES_BIG_ENDIAN ? (len - 1) - byte : byte;
+
+      value = (unsigned HOST_WIDE_INT) buffer[offset];
+
+      if (bitpos < HOST_BITS_PER_WIDE_INT)
+	result.low |= value << bitpos;
+      else
+	result.high |= value << (bitpos - HOST_BITS_PER_WIDE_INT);
+    }
+
+  return result;
+}
+
+
 /* Returns mask for PREC bits.  */
 
 double_int