tcg: rework liveness analysis
Rework the liveness analysis by tracking temps that need to go back to memory in addition to dead temps tracking. This allows to mark output arguments as "need sync", and to synchronize them back to memory as soon as they are not written anymore. This way even arguments mapping to globals can be marked as "dead", avoiding moves to a new register when input and outputs are aliased. In addition it means that registers are freed as soon as temps are not used anymore, instead of waiting for a basic block end or an op with side effects. This reduces register spilling especially on CPUs with few registers, and spread the mov over all the TB, increasing the performances on in-order CPUs. Reviewed-by: Richard Henderson <rth@twiddle.net> Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
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9c43b68de6
64
tcg/tcg.c
64
tcg/tcg.c
@ -1180,31 +1180,27 @@ static inline void tcg_set_nop(TCGContext *s, uint16_t *opc_ptr,
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}
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}
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}
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}
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/* liveness analysis: end of function: globals are live, temps are
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/* liveness analysis: end of function: all temps are dead, and globals
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dead. */
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should be in memory. */
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/* XXX: at this stage, not used as there would be little gains because
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static inline void tcg_la_func_end(TCGContext *s, uint8_t *dead_temps,
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most TBs end with a conditional jump. */
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uint8_t *mem_temps)
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static inline void tcg_la_func_end(TCGContext *s, uint8_t *dead_temps)
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{
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{
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memset(dead_temps, 0, s->nb_globals);
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memset(dead_temps, 1, s->nb_temps);
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memset(dead_temps + s->nb_globals, 1, s->nb_temps - s->nb_globals);
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memset(mem_temps, 1, s->nb_globals);
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memset(mem_temps + s->nb_globals, 0, s->nb_temps - s->nb_globals);
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}
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}
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/* liveness analysis: end of basic block: globals are live, temps are
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/* liveness analysis: end of basic block: all temps are dead, globals
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dead, local temps are live. */
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and local temps should be in memory. */
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static inline void tcg_la_bb_end(TCGContext *s, uint8_t *dead_temps)
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static inline void tcg_la_bb_end(TCGContext *s, uint8_t *dead_temps,
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uint8_t *mem_temps)
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{
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{
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int i;
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int i;
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TCGTemp *ts;
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memset(dead_temps, 0, s->nb_globals);
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memset(dead_temps, 1, s->nb_temps);
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ts = &s->temps[s->nb_globals];
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memset(mem_temps, 1, s->nb_globals);
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for(i = s->nb_globals; i < s->nb_temps; i++) {
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for(i = s->nb_globals; i < s->nb_temps; i++) {
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if (ts->temp_local)
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mem_temps[i] = s->temps[i].temp_local;
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dead_temps[i] = 0;
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else
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dead_temps[i] = 1;
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ts++;
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}
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}
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}
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}
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@ -1217,7 +1213,7 @@ static void tcg_liveness_analysis(TCGContext *s)
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TCGOpcode op;
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TCGOpcode op;
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TCGArg *args;
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TCGArg *args;
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const TCGOpDef *def;
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const TCGOpDef *def;
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uint8_t *dead_temps;
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uint8_t *dead_temps, *mem_temps;
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uint16_t dead_args;
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uint16_t dead_args;
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uint8_t sync_args;
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uint8_t sync_args;
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@ -1229,7 +1225,8 @@ static void tcg_liveness_analysis(TCGContext *s)
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s->op_sync_args = tcg_malloc(nb_ops * sizeof(uint8_t));
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s->op_sync_args = tcg_malloc(nb_ops * sizeof(uint8_t));
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dead_temps = tcg_malloc(s->nb_temps);
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dead_temps = tcg_malloc(s->nb_temps);
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memset(dead_temps, 1, s->nb_temps);
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mem_temps = tcg_malloc(s->nb_temps);
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tcg_la_func_end(s, dead_temps, mem_temps);
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args = gen_opparam_ptr;
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args = gen_opparam_ptr;
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op_index = nb_ops - 1;
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op_index = nb_ops - 1;
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@ -1253,8 +1250,9 @@ static void tcg_liveness_analysis(TCGContext *s)
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if (call_flags & TCG_CALL_PURE) {
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if (call_flags & TCG_CALL_PURE) {
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for(i = 0; i < nb_oargs; i++) {
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for(i = 0; i < nb_oargs; i++) {
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arg = args[i];
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arg = args[i];
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if (!dead_temps[arg])
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if (!dead_temps[arg] || mem_temps[arg]) {
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goto do_not_remove_call;
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goto do_not_remove_call;
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}
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}
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}
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tcg_set_nop(s, gen_opc_buf + op_index,
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tcg_set_nop(s, gen_opc_buf + op_index,
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args - 1, nb_args);
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args - 1, nb_args);
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@ -1269,12 +1267,17 @@ static void tcg_liveness_analysis(TCGContext *s)
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if (dead_temps[arg]) {
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if (dead_temps[arg]) {
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dead_args |= (1 << i);
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dead_args |= (1 << i);
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}
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}
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if (mem_temps[arg]) {
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sync_args |= (1 << i);
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}
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dead_temps[arg] = 1;
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dead_temps[arg] = 1;
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mem_temps[arg] = 0;
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}
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}
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if (!(call_flags & TCG_CALL_CONST)) {
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if (!(call_flags & TCG_CALL_CONST)) {
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/* globals are live (they may be used by the call) */
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/* globals should go back to memory */
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memset(dead_temps, 0, s->nb_globals);
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memset(dead_temps, 1, s->nb_globals);
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memset(mem_temps, 1, s->nb_globals);
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}
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}
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/* input args are live */
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/* input args are live */
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@ -1304,6 +1307,7 @@ static void tcg_liveness_analysis(TCGContext *s)
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args--;
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args--;
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/* mark the temporary as dead */
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/* mark the temporary as dead */
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dead_temps[args[0]] = 1;
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dead_temps[args[0]] = 1;
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mem_temps[args[0]] = 0;
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break;
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break;
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case INDEX_op_end:
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case INDEX_op_end:
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break;
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break;
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@ -1369,8 +1373,9 @@ static void tcg_liveness_analysis(TCGContext *s)
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if (!(def->flags & TCG_OPF_SIDE_EFFECTS) && nb_oargs != 0) {
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if (!(def->flags & TCG_OPF_SIDE_EFFECTS) && nb_oargs != 0) {
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for(i = 0; i < nb_oargs; i++) {
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for(i = 0; i < nb_oargs; i++) {
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arg = args[i];
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arg = args[i];
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if (!dead_temps[arg])
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if (!dead_temps[arg] || mem_temps[arg]) {
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goto do_not_remove;
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goto do_not_remove;
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}
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}
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}
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do_remove:
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do_remove:
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tcg_set_nop(s, gen_opc_buf + op_index, args, def->nb_args);
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tcg_set_nop(s, gen_opc_buf + op_index, args, def->nb_args);
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@ -1388,15 +1393,20 @@ static void tcg_liveness_analysis(TCGContext *s)
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if (dead_temps[arg]) {
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if (dead_temps[arg]) {
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dead_args |= (1 << i);
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dead_args |= (1 << i);
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}
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}
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if (mem_temps[arg]) {
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sync_args |= (1 << i);
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}
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dead_temps[arg] = 1;
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dead_temps[arg] = 1;
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mem_temps[arg] = 0;
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}
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}
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/* if end of basic block, update */
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/* if end of basic block, update */
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if (def->flags & TCG_OPF_BB_END) {
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if (def->flags & TCG_OPF_BB_END) {
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tcg_la_bb_end(s, dead_temps);
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tcg_la_bb_end(s, dead_temps, mem_temps);
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} else if (def->flags & TCG_OPF_CALL_CLOBBER) {
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} else if (def->flags & TCG_OPF_CALL_CLOBBER) {
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/* globals are live */
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/* globals should go back to memory */
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memset(dead_temps, 0, s->nb_globals);
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memset(dead_temps, 1, s->nb_globals);
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memset(mem_temps, 1, s->nb_globals);
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}
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}
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/* input args are live */
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/* input args are live */
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