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.
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2 changed files with 28 additions and 4 deletions
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@ -1,3 +1,8 @@
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2016-11-24 Andreas Arnez <arnez@linux.vnet.ibm.com>
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* dwarf2loc.c (copy_bitwise): Use memcpy for the middle part, if
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it is byte-aligned.
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2016-11-24 Andreas Arnez <arnez@linux.vnet.ibm.com>
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Pedro Alves <palves@redhat.com>
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@ -1548,11 +1548,30 @@ copy_bitwise (gdb_byte *dest, ULONGEST dest_offset,
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{
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size_t len = nbits / 8;
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while (len--)
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/* Use a faster method for byte-aligned copies. */
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if (avail == 0)
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{
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buf |= *(bits_big_endian ? source-- : source++) << avail;
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*(bits_big_endian ? dest-- : dest++) = buf;
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buf >>= 8;
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if (bits_big_endian)
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{
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dest -= len;
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source -= len;
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memcpy (dest + 1, source + 1, len);
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}
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else
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{
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memcpy (dest, source, len);
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dest += len;
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source += len;
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}
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}
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else
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{
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while (len--)
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{
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buf |= *(bits_big_endian ? source-- : source++) << avail;
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*(bits_big_endian ? dest-- : dest++) = buf;
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buf >>= 8;
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}
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}
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nbits %= 8;
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}
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