On Linux if you just
echo 'int main(int ac,char**av){return 0;}' >/dev/shm/true.c
And then time (with high resolution) `tcc -run /dev/shm/true.c`,
you get execution time about 2X longer than the same with `tcc -c`.
Running strace on the linking revealed hundreds of read(,,1)'s.
Looking into it further, these are all from tccelf.c:ld_inp()
which it seems was added by grischka in 2019 for multi-threading.
I might even guess the unbuffered reads were a "placeholder" that
never got replaced.
If you first apply the attached patch and do the same thing, most
unneeded system call overhead vanishes and the end-to-end time (of,
yes, that trivial program) gets 1.35X better (on an i7-6700k it goes
down to 750 microsec from 1000 microsec with statistical errors
around +-10 microsec). The size expansion of TCCState is not so
bad -- 272 bytes added to the 1808 byte struct or +15%.
cb
diff --git a/tcc.h b/tcc.h
index 687fb607..71cf4e5a 100644
--- a/tcc.h
+++ b/tcc.h
@@ -1002,6 +1002,8 @@ struct TCCState {
int argc;
char **argv;
CString linker_arg; /* collect -Wl options */
+ int ioBufN; /* number of bytes used in ioBuf */
+ char ioBuf[256], *ioBufP; /* A small IO buffer & ptr */
};
struct filespec {
diff --git a/tccelf.c b/tccelf.c
index 8e11c1bf..cd588b8e 100644
--- a/tccelf.c
+++ b/tccelf.c
@@ -3799,17 +3799,25 @@ ST_FUNC int tcc_load_dll(TCCState *s1, int fd, const char *filename, int level)
#define LD_TOK_NAME 256
#define LD_TOK_EOF (-1)
+static char ioBufFill(TCCState *s1) {
+ int m = read(s1->fd, s1->ioBuf, sizeof s1->ioBuf);
+ if (m > 0) {
+ s1->ioBufP = &s1->ioBuf[1];
+ s1->ioBufN = m - 1;
+ return s1->ioBuf[0];
+ }
+ return CH_EOF;
+}
+#define TCC_GETCH(s1) ((s1)->ioBufN-- > 0 ? *(s1)->ioBufP++ : ioBufFill((s1)))
+
static int ld_inp(TCCState *s1)
{
- char b;
if (s1->cc != -1) {
int c = s1->cc;
s1->cc = -1;
return c;
}
- if (1 == read(s1->fd, &b, 1))
- return b;
- return CH_EOF;
+ return TCC_GETCH(s1);
}
/* return next ld script token */
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