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Optimize byte-aligned copies in copy_bitwise() 

The function copy_bitwise used for copying DWARF pieces can potentially
be invoked for large chunks of data.  For instance, consider a large
struct one of whose members is currently located in a register.  In this
case copy_bitwise would still copy the data bitwise in a loop, which is
much slower than necessary.

This change uses memcpy for the large part instead, if possible.

gdb/ChangeLog:

	* dwarf2loc.c (copy_bitwise): Use memcpy for the middle part, if
	it is byte-aligned.
This commit is contained in:
Andreas Arnez 2016-11-24 17:48:04 +01:00
parent ad06383f10
commit 793c128d03
2 changed files with 28 additions and 4 deletions
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5
gdb/ChangeLog
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@ -1,3 +1,8 @@
2016-11-24 Andreas Arnez <arnez@linux.vnet.ibm.com>
* dwarf2loc.c (copy_bitwise): Use memcpy for the middle part, if
it is byte-aligned.
2016-11-24 Andreas Arnez <arnez@linux.vnet.ibm.com>
Pedro Alves <palves@redhat.com>

27
gdb/dwarf2loc.c
View File

@ -1548,11 +1548,30 @@ copy_bitwise (gdb_byte *dest, ULONGEST dest_offset,
{
size_t len = nbits / 8;
while (len--)
/* Use a faster method for byte-aligned copies. */
if (avail == 0)
{
buf |= *(bits_big_endian ? source-- : source++) << avail;
*(bits_big_endian ? dest-- : dest++) = buf;
buf >>= 8;
if (bits_big_endian)
{
dest -= len;
source -= len;
memcpy (dest + 1, source + 1, len);
}
else
{
memcpy (dest, source, len);
dest += len;
source += len;
}
}
else
{
while (len--)
{
buf |= *(bits_big_endian ? source-- : source++) << avail;
*(bits_big_endian ? dest-- : dest++) = buf;
buf >>= 8;
}
}
nbits %= 8;
}