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Use strchr/memmove in collapse_continuations.

Browse Source 
collapse_continuations is already using strchr to speed up the
common case of no backslash-newline sequence, but on modern
processors it is faster to scan the string twice with
strchr+memmove (or strlen+memmove) than to move bytes manually.

Saves about 1.5% on QEMU's no-op build (from 11.37s to 11.23s).

* misc.c (collapse_continuations): Rewrite the scanning of LINE.
This commit is contained in:
Paolo Bonzini 2017-08-11 13:44:30 +02:00 committed by Paul Smith
parent 0c5a9f9b92
commit ef7a1b7d6e
1 changed files with 33 additions and 49 deletions
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82
misc.c
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@ -55,43 +55,41 @@ alpha_compare (const void *v1, const void *v2)
void
collapse_continuations (char *line)
{
char *in, *out, *p;
char *out = line;
char *in = line;
char *q;
in = strchr (line, '\n');
if (in == 0)
q = strchr(in, '\n');
if (q == 0)
return;
out = in;
while (out > line && out[-1] == '\\')
--out;
while (*in != '\0')
do
{
/* BS_WRITE gets the number of quoted backslashes at
the end just before IN, and BACKSLASH gets nonzero
if the next character is quoted. */
unsigned int backslash = 0;
unsigned int bs_write = 0;
for (p = in - 1; p >= line && *p == '\\'; --p)
char *p = q;
int i;
int out_line_length;
if (q > line && q[-1] == '\\')
{
if (backslash)
++bs_write;
backslash = !backslash;
/* It should be impossible to go back this far without exiting,
but if we do, we can't get the right answer. */
if (in == out - 1)
abort ();
/* Search for more backslashes. */
i = -2;
while (&p[i] >= line && p[i] == '\\')
--i;
++i;
}
else
i = 0;
/* Output the appropriate number of backslashes. */
while (bs_write-- > 0)
*out++ = '\\';
/* The number of backslashes is now -I, keep half of them. */
out_line_length = (p - in) + i - i/2;
if (out != in)
memmove (out, in, out_line_length);
out += out_line_length;
/* Skip the newline. */
++in;
/* When advancing IN, skip the newline too. */
in = q + 1;
if (backslash)
if (i & 1)
{
/* Backslash/newline handling:
In traditional GNU make all trailing whitespace, consecutive
@ -106,30 +104,16 @@ collapse_continuations (char *line)
*out++ = ' ';
}
else
/* If the newline isn't quoted, put it in the output. */
*out++ = '\n';
{
/* If the newline isn't quoted, put it in the output. */
*out++ = '\n';
}
/* Now copy the following line to the output.
Stop when we find backslashes followed by a newline. */
while (*in != '\0')
if (*in == '\\')
{
p = in + 1;
while (*p == '\\')
++p;
if (*p == '\n')
{
in = p;
break;
}
while (in < p)
*out++ = *in++;
}
else
*out++ = *in++;
q = strchr(in, '\n');
}
while (q);
*out = '\0';
memmove(out, in, strlen(in) + 1);
}
/* Print N spaces (used in debug for target-depth). */