From 793c128d03113816db85e8d1fa0bcd4982e246ee Mon Sep 17 00:00:00 2001 From: Andreas Arnez Date: Thu, 24 Nov 2016 17:48:04 +0100 Subject: [PATCH] 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. --- gdb/ChangeLog | 5 +++++ gdb/dwarf2loc.c | 27 +++++++++++++++++++++++---- 2 files changed, 28 insertions(+), 4 deletions(-) diff --git a/gdb/ChangeLog b/gdb/ChangeLog index d667a37481..51787adf01 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,8 @@ +2016-11-24 Andreas Arnez + + * dwarf2loc.c (copy_bitwise): Use memcpy for the middle part, if + it is byte-aligned. + 2016-11-24 Andreas Arnez Pedro Alves diff --git a/gdb/dwarf2loc.c b/gdb/dwarf2loc.c index 61f197b279..128f65468b 100644 --- a/gdb/dwarf2loc.c +++ b/gdb/dwarf2loc.c @@ -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; } -- 2.34.1