read/write_pieced_value: Improve logic for buffer allocation

So far the main loop in read_pieced_value and write_pieced_value is
structured like this:

(1) Prepare a buffer and some variables we may need;

(2) depending on the DWARF piece type to be handled, use the buffer and
    the prepared variables, ignore them, or even recalculate them.

This approach reduces readability and may also lead to unnecessary copying
of data.  This patch moves the preparations to the places where sufficient
information is available and removes some of the variables involved.

gdb/ChangeLog:

	* dwarf2loc.c (read_pieced_value): Move the buffer allocation and
	some other preparations to the places where sufficient information
	is available.
	(write_pieced_value): Likewise.

1 files changed, 7 insertions, 0 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 8c022a4..a177e8e 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,12 @@
 2017-06-13  Andreas Arnez  <arnez@linux.vnet.ibm.com>
 
+	* dwarf2loc.c (read_pieced_value): Move the buffer allocation and
+	some other preparations to the places where sufficient information
+	is available.
+	(write_pieced_value): Likewise.
+
+2017-06-13  Andreas Arnez  <arnez@linux.vnet.ibm.com>
+
 	* dwarf2loc.c (bits_to_bytes): New function.
 	(read_pieced_value): Fix offset calculations for register pieces
 	on big-endian targets.