read/write_pieced_value: Remove unnecessary variable copies

In read_pieced_value's main loop, the variables `dest_offset_bits' and
`source_offset_bits' are basically just copies of `offset' and
`bits_to_skip', respectively.  In write_pieced_value the copies are
reversed.  This is not very helpful when trying to keep the logic between
these functions in sync.  Since the copies are unnecessary, this patch
just removes them.

gdb/ChangeLog:

	* dwarf2loc.c (read_pieced_value): Remove unnecessary variables
	dest_offset_bits and source_offset_bits.
	(write_pieced_value): Likewise.

2 files changed, 58 insertions, 68 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 1d383cc..6ca4b5c 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,11 @@
 2017-06-13  Andreas Arnez  <arnez@linux.vnet.ibm.com>
 
+	* dwarf2loc.c (read_pieced_value): Remove unnecessary variables
+	dest_offset_bits and source_offset_bits.
+	(write_pieced_value): Likewise.
+
+2017-06-13  Andreas Arnez  <arnez@linux.vnet.ibm.com>
+
 	* dwarf2loc.c (read_pieced_value): Respect the piece offset, as
 	given by DW_OP_bit_piece.
 	(write_pieced_value): Likewise.
diff --git a/gdb/dwarf2loc.c b/gdb/dwarf2loc.c
index 23901f0e7..ed5b29c 100644
--- a/gdb/dwarf2loc.c
+++ b/gdb/dwarf2loc.c
@@ -1790,25 +1790,16 @@ read_pieced_value (struct value *v)
   else
     max_offset = 8 * TYPE_LENGTH (value_type (v));
 
-  for (i = 0; i < c->n_pieces && offset < max_offset; i++)
+  /* Advance to the first non-skipped piece.  */
+  for (i = 0; i < c->n_pieces && bits_to_skip >= c->pieces[i].size; i++)
+    bits_to_skip -= c->pieces[i].size;
+
+  for (; i < c->n_pieces && offset < max_offset; i++)
     {
       struct dwarf_expr_piece *p = &c->pieces[i];
       size_t this_size, this_size_bits;
-      long dest_offset_bits, source_offset_bits;
-
-      /* Compute size, source, and destination offsets for copying, in
-	 bits.  */
-      this_size_bits = p->size;
-      if (bits_to_skip > 0 && bits_to_skip >= this_size_bits)
-	{
-	  bits_to_skip -= this_size_bits;
-	  continue;
-	}
-      source_offset_bits = bits_to_skip;
-      this_size_bits -= bits_to_skip;
-      bits_to_skip = 0;
-      dest_offset_bits = offset;
 
+      this_size_bits = p->size - bits_to_skip;
       if (this_size_bits > max_offset - offset)
 	this_size_bits = max_offset - offset;
 
@@ -1827,16 +1818,16 @@ read_pieced_value (struct value *v)
 		&& p->offset + p->size < reg_bits)
 	      {
 		/* Big-endian, and we want less than full size.  */
-		source_offset_bits += reg_bits - (p->offset + p->size);
+		bits_to_skip += reg_bits - (p->offset + p->size);
 	      }
 	    else
-	      source_offset_bits += p->offset;
+	      bits_to_skip += p->offset;
 
-	    this_size = bits_to_bytes (source_offset_bits, this_size_bits);
+	    this_size = bits_to_bytes (bits_to_skip, this_size_bits);
 	    buffer.reserve (this_size);
 
 	    if (!get_frame_register_bytes (frame, gdb_regnum,
-					   source_offset_bits / 8,
+					   bits_to_skip / 8,
 					   this_size, buffer.data (),
 					   &optim, &unavail))
 	      {
@@ -1846,24 +1837,23 @@ read_pieced_value (struct value *v)
 		  mark_value_bits_unavailable (v, offset, this_size_bits);
 		break;
 	      }
-
-	    copy_bitwise (contents, dest_offset_bits,
-			  buffer.data (), source_offset_bits % 8,
+	    copy_bitwise (contents, offset,
+			  buffer.data (), bits_to_skip % 8,
 			  this_size_bits, bits_big_endian);
 	  }
 	  break;
 
 	case DWARF_VALUE_MEMORY:
-	  source_offset_bits += p->offset;
-	  this_size = bits_to_bytes (source_offset_bits, this_size_bits);
+	  bits_to_skip += p->offset;
+	  this_size = bits_to_bytes (bits_to_skip, this_size_bits);
 	  buffer.reserve (this_size);
 
 	  read_value_memory (v, offset,
 			     p->v.mem.in_stack_memory,
-			     p->v.mem.addr + source_offset_bits / 8,
+			     p->v.mem.addr + bits_to_skip / 8,
 			     buffer.data (), this_size);
-	  copy_bitwise (contents, dest_offset_bits,
-			buffer.data (), source_offset_bits % 8,
+	  copy_bitwise (contents, offset,
+			buffer.data (), bits_to_skip % 8,
 			this_size_bits, bits_big_endian);
 	  break;
 
@@ -1880,14 +1870,13 @@ read_pieced_value (struct value *v)
 
 	    /* Piece is anchored at least significant bit end.  */
 	    if (gdbarch_byte_order (objfile_gdbarch) == BFD_ENDIAN_BIG)
-	      source_offset_bits += (stack_value_size_bits
-				     - p->offset - p->size);
+	      bits_to_skip += stack_value_size_bits - p->offset - p->size;
 	    else
-	      source_offset_bits += p->offset;
+	      bits_to_skip += p->offset;
 
-	    copy_bitwise (contents, dest_offset_bits,
+	    copy_bitwise (contents, offset,
 			  value_contents_all (p->v.value),
-			  source_offset_bits,
+			  bits_to_skip,
 			  this_size_bits, bits_big_endian);
 	  }
 	  break;
@@ -1898,14 +1887,14 @@ read_pieced_value (struct value *v)
 	    size_t n = this_size_bits;
 
 	    /* Cut off at the end of the implicit value.  */
-	    source_offset_bits += p->offset;
-	    if (source_offset_bits >= literal_size_bits)
+	    bits_to_skip += p->offset;
+	    if (bits_to_skip >= literal_size_bits)
 	      break;
-	    if (n > literal_size_bits - source_offset_bits)
-	      n = literal_size_bits - source_offset_bits;
+	    if (n > literal_size_bits - bits_to_skip)
+	      n = literal_size_bits - bits_to_skip;
 
-	    copy_bitwise (contents, dest_offset_bits,
-			  p->v.literal.data, source_offset_bits,
+	    copy_bitwise (contents, offset,
+			  p->v.literal.data, bits_to_skip,
 			  n, bits_big_endian);
 	  }
 	  break;
@@ -1924,6 +1913,7 @@ read_pieced_value (struct value *v)
 	}
 
       offset += this_size_bits;
+      bits_to_skip = 0;
     }
 }
 
@@ -1959,23 +1949,16 @@ write_pieced_value (struct value *to, struct value *from)
   else
     max_offset = 8 * TYPE_LENGTH (value_type (to));
 
-  for (i = 0; i < c->n_pieces && offset < max_offset; i++)
+  /* Advance to the first non-skipped piece.  */
+  for (i = 0; i < c->n_pieces && bits_to_skip >= c->pieces[i].size; i++)
+    bits_to_skip -= c->pieces[i].size;
+
+  for (; i < c->n_pieces && offset < max_offset; i++)
     {
       struct dwarf_expr_piece *p = &c->pieces[i];
       size_t this_size_bits, this_size;
-      long dest_offset_bits, source_offset_bits;
-
-      this_size_bits = p->size;
-      if (bits_to_skip > 0 && bits_to_skip >= this_size_bits)
-	{
-	  bits_to_skip -= this_size_bits;
-	  continue;
-	}
-      dest_offset_bits = bits_to_skip;
-      this_size_bits -= bits_to_skip;
-      bits_to_skip = 0;
-      source_offset_bits = offset;
 
+      this_size_bits = p->size - bits_to_skip;
       if (this_size_bits > max_offset - offset)
 	this_size_bits = max_offset - offset;
 
@@ -1992,22 +1975,22 @@ write_pieced_value (struct value *to, struct value *from)
 		&& p->offset + p->size < reg_bits)
 	      {
 		/* Big-endian, and we want less than full size.  */
-		dest_offset_bits += reg_bits - (p->offset + p->size);
+		bits_to_skip += reg_bits - (p->offset + p->size);
 	      }
 	    else
-	      dest_offset_bits += p->offset;
+	      bits_to_skip += p->offset;
 
-	    this_size = bits_to_bytes (dest_offset_bits, this_size_bits);
+	    this_size = bits_to_bytes (bits_to_skip, this_size_bits);
 	    buffer.reserve (this_size);
 
-	    if (dest_offset_bits % 8 != 0 || this_size_bits % 8 != 0)
+	    if (bits_to_skip % 8 != 0 || this_size_bits % 8 != 0)
 	      {
 		/* Data is copied non-byte-aligned into the register.
 		   Need some bits from original register value.  */
 		int optim, unavail;
 
 		if (!get_frame_register_bytes (frame, gdb_regnum,
-					       dest_offset_bits / 8,
+					       bits_to_skip / 8,
 					       this_size, buffer.data (),
 					       &optim, &unavail))
 		  {
@@ -2024,34 +2007,34 @@ write_pieced_value (struct value *to, struct value *from)
 		  }
 	      }
 
-	    copy_bitwise (buffer.data (), dest_offset_bits % 8,
-			  contents, source_offset_bits,
+	    copy_bitwise (buffer.data (), bits_to_skip % 8,
+			  contents, offset,
 			  this_size_bits, bits_big_endian);
 	    put_frame_register_bytes (frame, gdb_regnum,
-				      dest_offset_bits / 8,
+				      bits_to_skip / 8,
 				      this_size, buffer.data ());
 	  }
 	  break;
 	case DWARF_VALUE_MEMORY:
 	  {
-	    dest_offset_bits += p->offset;
+	    bits_to_skip += p->offset;
 
-	    CORE_ADDR start_addr = p->v.mem.addr + dest_offset_bits / 8;
+	    CORE_ADDR start_addr = p->v.mem.addr + bits_to_skip / 8;
 
-	    if (dest_offset_bits % 8 == 0 && this_size_bits % 8 == 0
-		&& source_offset_bits % 8 == 0)
+	    if (bits_to_skip % 8 == 0 && this_size_bits % 8 == 0
+		&& offset % 8 == 0)
 	      {
 		/* Everything is byte-aligned; no buffer needed.  */
 		write_memory (start_addr,
-			      contents + source_offset_bits / 8,
+			      contents + offset / 8,
 			      this_size_bits / 8);
 		break;
 	      }
 
-	    this_size = bits_to_bytes (dest_offset_bits, this_size_bits);
+	    this_size = bits_to_bytes (bits_to_skip, this_size_bits);
 	    buffer.reserve (this_size);
 
-	    if (dest_offset_bits % 8 != 0 || this_size_bits % 8 != 0)
+	    if (bits_to_skip % 8 != 0 || this_size_bits % 8 != 0)
 	      {
 		if (this_size <= 8)
 		  {
@@ -2068,8 +2051,8 @@ write_pieced_value (struct value *to, struct value *from)
 		  }
 	      }
 
-	    copy_bitwise (buffer.data (), dest_offset_bits % 8,
-			  contents, source_offset_bits,
+	    copy_bitwise (buffer.data (), bits_to_skip % 8,
+			  contents, offset,
 			  this_size_bits, bits_big_endian);
 	    write_memory (start_addr, buffer.data (), this_size);
 	  }
@@ -2079,6 +2062,7 @@ write_pieced_value (struct value *to, struct value *from)
 	  break;
 	}
       offset += this_size_bits;
+      bits_to_skip = 0;
     }
 }