Cache tcp->u_nargs in a local variable for for() loops

Loops of the form "for (i = 0; i < tcp->u_nargs; i++) ..."
need to fetch tcp->u_nargs from memory on every iteration
if "..." part has a function call (gcc doesn't know that
tcp->u_nargs won't change). This can be sped up
by putting tcp->u_nargs in a local variable, which might
go into a CPU register.

* syscall.c (decode_subcall): Cache tcp->u_nargs in a local variable
as for() loop limit value.
(syscall_enter): Likewise.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>

diff --git a/syscall.c b/syscall.c
index 85c8009a8978cdb9cfc81645c20a157e325618a1..2af908573a8b541c11cc1b4b214c2203570fc361 100644 (file)
--- a/syscall.c
+++ b/syscall.c
@@ -570,7 +570,7 @@ static void
 decode_subcall(struct tcb *tcp, int subcall, int nsubcalls, enum subcall_style style)
 {
        unsigned long addr, mask;
-       int i;
+       int i, n;
        int size = personality_wordsize[current_personality];
 
        switch (style) {
@@ -578,8 +578,8 @@ decode_subcall(struct tcb *tcp, int subcall, int nsubcalls, enum subcall_style s
                if (tcp->u_arg[0] < 0 || tcp->u_arg[0] >= nsubcalls)
                        return;
                tcp->scno = subcall + tcp->u_arg[0];
-               tcp->u_nargs = sysent[tcp->scno].nargs;
-               for (i = 0; i < tcp->u_nargs; i++)
+               tcp->u_nargs = n = sysent[tcp->scno].nargs;
+               for (i = 0; i < n; i++)
                        tcp->u_arg[i] = tcp->u_arg[i + 1];
                break;
        case deref_style:
@@ -587,7 +587,8 @@ decode_subcall(struct tcb *tcp, int subcall, int nsubcalls, enum subcall_style s
                        return;
                tcp->scno = subcall + tcp->u_arg[0];
                addr = tcp->u_arg[1];
-               for (i = 0; i < sysent[tcp->scno].nargs; i++) {
+               tcp->u_nargs = n = sysent[tcp->scno].nargs;
+               for (i = 0; i < n; i++) {
                        if (size == sizeof(int)) {
                                unsigned int arg;
                                if (umove(tcp, addr, &arg) < 0)
@@ -604,7 +605,6 @@ decode_subcall(struct tcb *tcp, int subcall, int nsubcalls, enum subcall_style s
                                abort();
                        addr += size;
                }
-               tcp->u_nargs = sysent[tcp->scno].nargs;
                break;
        case mask_style:
                mask = (tcp->u_arg[0] >> 8) & 0xff;
@@ -2124,12 +2124,12 @@ syscall_enter(struct tcb *tcp)
 #  ifndef PT_ORIG_R3
 #   define PT_ORIG_R3 34
 #  endif
-       int i;
+       int i, nargs;
        if (tcp->scno >= 0 && tcp->scno < nsyscalls)
-               tcp->u_nargs = sysent[tcp->scno].nargs;
+               nargs = tcp->u_nargs = sysent[tcp->scno].nargs;
        else
-               tcp->u_nargs = MAX_ARGS;
-       for (i = 0; i < tcp->u_nargs; i++) {
+               nargs = tcp->u_nargs = MAX_ARGS;
+       for (i = 0; i < nargs; i++) {
                if (upeek(tcp, (i==0) ?
                        (sizeof(unsigned long) * PT_ORIG_R3) :
                        ((i+PT_R3) * sizeof(unsigned long)),
@@ -2145,12 +2145,12 @@ syscall_enter(struct tcb *tcp)
        for (i = 0; i < tcp->u_nargs; i++)
                tcp->u_arg[i] = regs.u_regs[U_REG_O0 + i];
 # elif defined(HPPA)
-       int i;
+       int i, nargs;
        if (tcp->scno >= 0 && tcp->scno < nsyscalls)
-               tcp->u_nargs = sysent[tcp->scno].nargs;
+               nargs = tcp->u_nargs = sysent[tcp->scno].nargs;
        else
-               tcp->u_nargs = MAX_ARGS;
-       for (i = 0; i < tcp->u_nargs; i++) {
+               nargs = tcp->u_nargs = MAX_ARGS;
+       for (i = 0; i < nargs; i++) {
                if (upeek(tcp, PT_GR26-4*i, &tcp->u_arg[i]) < 0)
                        return -1;
        }
@@ -2171,26 +2171,26 @@ syscall_enter(struct tcb *tcp)
        tcp->u_arg[4] = regs.r5;
        tcp->u_arg[5] = regs.r3;
 # elif defined(BFIN)
-       int i;
+       int i, nargs;
        static const int argreg[] = { PT_R0, PT_R1, PT_R2, PT_R3, PT_R4, PT_R5 };
 
        if (tcp->scno >= 0 && tcp->scno < nsyscalls)
-               tcp->u_nargs = sysent[tcp->scno].nargs;
+               nargs = tcp->u_nargs = sysent[tcp->scno].nargs;
        else
-               tcp->u_nargs = ARRAY_SIZE(argreg);
+               nargs = tcp->u_nargs = ARRAY_SIZE(argreg);
 
-       for (i = 0; i < tcp->u_nargs; ++i)
+       for (i = 0; i < nargs; ++i)
                if (upeek(tcp, argreg[i], &tcp->u_arg[i]) < 0)
                        return -1;
 # elif defined(SH)
-       int i;
+       int i, nargs;
        static const int syscall_regs[] = {
                4 * (REG_REG0+4), 4 * (REG_REG0+5), 4 * (REG_REG0+6), 4 * (REG_REG0+7),
                4 * (REG_REG0  ), 4 * (REG_REG0+1), 4 * (REG_REG0+2)
        };
 
-       tcp->u_nargs = sysent[tcp->scno].nargs;
-       for (i = 0; i < tcp->u_nargs; i++) {
+       nargs = tcp->u_nargs = sysent[tcp->scno].nargs;
+       for (i = 0; i < nargs; i++) {
                if (upeek(tcp, syscall_regs[i], &tcp->u_arg[i]) < 0)
                        return -1;
        }
@@ -2207,90 +2207,90 @@ syscall_enter(struct tcb *tcp)
        assert(sysent[tcp->scno].nargs < ARRAY_SIZE(syscall_regs));
         */
 
-       tcp->u_nargs = sysent[tcp->scno].nargs;
-       for (i = 0; i < tcp->u_nargs; i++) {
+       nargs = tcp->u_nargs = sysent[tcp->scno].nargs;
+       for (i = 0; i < nargs; i++) {
                if (upeek(tcp, REG_GENERAL(syscall_regs[i]), &tcp->u_arg[i]) < 0)
                        return -1;
        }
 # elif defined(X86_64)
-       int i;
+       int i, nargs;
        static const int argreg[SUPPORTED_PERSONALITIES][MAX_ARGS] = {
                { 8 * RDI, 8 * RSI, 8 * RDX, 8 * R10, 8 * R8 , 8 * R9  }, /* x86-64 ABI */
                { 8 * RBX, 8 * RCX, 8 * RDX, 8 * RSI, 8 * RDI, 8 * RBP }  /* i386 ABI */
        };
 
        if (tcp->scno >= 0 && tcp->scno < nsyscalls)
-               tcp->u_nargs = sysent[tcp->scno].nargs;
+               nargs = tcp->u_nargs = sysent[tcp->scno].nargs;
        else
-               tcp->u_nargs = MAX_ARGS;
-       for (i = 0; i < tcp->u_nargs; i++) {
+               nargs = tcp->u_nargs = MAX_ARGS;
+       for (i = 0; i < nargs; i++) {
                if (upeek(tcp, argreg[current_personality][i], &tcp->u_arg[i]) < 0)
                        return -1;
        }
 # elif defined(MICROBLAZE)
-       int i;
+       int i, nargs;
        if (tcp->scno >= 0 && tcp->scno < nsyscalls)
-               tcp->u_nargs = sysent[tcp->scno].nargs;
+               nargs = tcp->u_nargs = sysent[tcp->scno].nargs;
        else
-               tcp->u_nargs = 0;
-       for (i = 0; i < tcp->u_nargs; i++) {
+               nargs = tcp->u_nargs = 0;
+       for (i = 0; i < nargs; i++) {
                if (upeek(tcp, (5 + i) * 4, &tcp->u_arg[i]) < 0)
                        return -1;
        }
 # elif defined(CRISV10) || defined(CRISV32)
-       int i;
+       int i, nargs;
        static const int crisregs[] = {
                4*PT_ORIG_R10, 4*PT_R11, 4*PT_R12,
                4*PT_R13     , 4*PT_MOF, 4*PT_SRP
        };
 
        if (tcp->scno >= 0 && tcp->scno < nsyscalls)
-               tcp->u_nargs = sysent[tcp->scno].nargs;
+               nargs = tcp->u_nargs = sysent[tcp->scno].nargs;
        else
-               tcp->u_nargs = 0;
-       for (i = 0; i < tcp->u_nargs; i++) {
+               nargs = tcp->u_nargs = 0;
+       for (i = 0; i < nargs; i++) {
                if (upeek(tcp, crisregs[i], &tcp->u_arg[i]) < 0)
                        return -1;
        }
 # elif defined(TILE)
-       int i;
+       int i, nargs;
        if (tcp->scno >= 0 && tcp->scno < nsyscalls)
-               tcp->u_nargs = sysent[tcp->scno].nargs;
+               nargs = tcp->u_nargs = sysent[tcp->scno].nargs;
        else
-               tcp->u_nargs = MAX_ARGS;
-       for (i = 0; i < tcp->u_nargs; ++i) {
+               nargs = tcp->u_nargs = MAX_ARGS;
+       for (i = 0; i < nargs; ++i) {
                if (upeek(tcp, PTREGS_OFFSET_REG(i), &tcp->u_arg[i]) < 0)
                        return -1;
        }
 # elif defined(M68K)
-       int i;
+       int i, nargs;
        if (tcp->scno >= 0 && tcp->scno < nsyscalls)
-               tcp->u_nargs = sysent[tcp->scno].nargs;
+               nargs = tcp->u_nargs = sysent[tcp->scno].nargs;
        else
-               tcp->u_nargs = MAX_ARGS;
-       for (i = 0; i < tcp->u_nargs; i++) {
+               nargs = tcp->u_nargs = MAX_ARGS;
+       for (i = 0; i < nargs; i++) {
                if (upeek(tcp, (i < 5 ? i : i + 2)*4, &tcp->u_arg[i]) < 0)
                        return -1;
        }
 # else /* Other architecture (like i386) (32bits specific) */
-       int i;
+       int i, nargs;
        if (tcp->scno >= 0 && tcp->scno < nsyscalls)
-               tcp->u_nargs = sysent[tcp->scno].nargs;
+               nargs = tcp->u_nargs = sysent[tcp->scno].nargs;
        else
-               tcp->u_nargs = MAX_ARGS;
-       for (i = 0; i < tcp->u_nargs; i++) {
+               nargs = tcp->u_nargs = MAX_ARGS;
+       for (i = 0; i < nargs; i++) {
                if (upeek(tcp, i*4, &tcp->u_arg[i]) < 0)
                        return -1;
        }
 # endif
 #endif /* LINUX */
 #ifdef SUNOS4
-       int i;
+       int i, nargs;
        if (tcp->scno >= 0 && tcp->scno < nsyscalls)
-               tcp->u_nargs = sysent[tcp->scno].nargs;
+               nargs = tcp->u_nargs = sysent[tcp->scno].nargs;
        else
-               tcp->u_nargs = MAX_ARGS;
-       for (i = 0; i < tcp->u_nargs; i++) {
+               nargs = tcp->u_nargs = MAX_ARGS;
+       for (i = 0; i < nargs; i++) {
                struct user *u;
 
                if (upeek(tcp, uoff(u_arg[0]) +