On Fri, May 20, 2011 at 04:39:29PM +0400, Kirill Batuzov wrote:
> Make tcg_constant_folding do copy and constant propagation. It is a
> preparational work before actual constant folding.
>
> Signed-off-by: Kirill Batuzov <batuz...@ispras.ru>
> ---
> tcg/optimize.c | 123
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 files changed, 123 insertions(+), 0 deletions(-)
>
> diff --git a/tcg/optimize.c b/tcg/optimize.c
> index cf31d18..a761c51 100644
> --- a/tcg/optimize.c
> +++ b/tcg/optimize.c
> @@ -31,22 +31,139 @@
> #include "qemu-common.h"
> #include "tcg-op.h"
>
> +typedef enum {
> + TCG_TEMP_UNDEF = 0,
> + TCG_TEMP_CONST,
> + TCG_TEMP_COPY,
> + TCG_TEMP_ANY
> +} tcg_temp_state;
> +
> +static int mov_to_movi(int op)
> +{
> + switch (op) {
> + case INDEX_op_mov_i32: return INDEX_op_movi_i32;
> +#if TCG_TARGET_REG_BITS == 64
> + case INDEX_op_mov_i64: return INDEX_op_movi_i64;
> +#endif
> + default:
> + fprintf(stderr, "Unrecognized operation %d in mov_to_movi.\n", op);
> + tcg_abort();
> + }
> +}
> +
> +/* Reset TEMP's state to TCG_TEMP_ANY. If TEMP was a representative of some
> + class of equivalent temp's, a new representative should be chosen in this
> + class. */
> +static void reset_temp(tcg_temp_state *state, tcg_target_ulong *vals,
> + TCGArg temp, int nb_temps, int nb_globals)
> +{
> + int i;
> + TCGArg new_base;
> + new_base = (TCGArg)-1;
> + for (i = nb_globals; i < nb_temps; i++) {
> + if (state[i] == TCG_TEMP_COPY && vals[i] == temp) {
> + if (new_base == ((TCGArg)-1)) {
> + new_base = (TCGArg)i;
> + state[i] = TCG_TEMP_ANY;
> + } else {
> + vals[i] = new_base;
> + }
> + }
> + }
> + for (i = 0; i < nb_globals; i++) {
> + if (state[i] == TCG_TEMP_COPY && vals[i] == temp) {
> + if (new_base == ((TCGArg)-1)) {
> + state[i] = TCG_TEMP_ANY;
> + } else {
> + vals[i] = new_base;
> + }
> + }
> + }
> + state[temp] = TCG_TEMP_ANY;
> +}
> +
> +/* Propagate constants and copies, fold constant expressions. */
> static TCGArg *tcg_constant_folding(TCGContext *s, uint16_t *tcg_opc_ptr,
> TCGArg *args, TCGOpDef *tcg_op_defs)
> {
> int i, nb_ops, op_index, op, nb_temps, nb_globals;
> const TCGOpDef *def;
> TCGArg *gen_args;
> + /* Array VALS has an element for each temp.
> + If this temp holds a constant then its value is kept in VALS' element.
> + If this temp is a copy of other ones then this equivalence class'
> + representative is kept in VALS' element.
> + If this temp is neither copy nor constant then corresponding VALS'
> + element is unused. */
> + static tcg_target_ulong vals[TCG_MAX_TEMPS];
> + static tcg_temp_state state[TCG_MAX_TEMPS];
>
> nb_temps = s->nb_temps;
> nb_globals = s->nb_globals;
> + memset(state, 0, nb_temps * sizeof(tcg_temp_state));
>
> nb_ops = tcg_opc_ptr - gen_opc_buf;
> gen_args = args;
> for (op_index = 0; op_index < nb_ops; op_index++) {
> op = gen_opc_buf[op_index];
> def = &tcg_op_defs[op];
> + /* Do copy propagation */
> + if (op != INDEX_op_call) {
> + for (i = def->nb_oargs; i < def->nb_oargs + def->nb_iargs; i++) {
> + if (state[args[i]] == TCG_TEMP_COPY
> + && !(def->args_ct[i].ct & TCG_CT_IALIAS)
> + && (def->args_ct[i].ct & TCG_CT_REG)) {
> + args[i] = vals[args[i]];
> + }
> + }
> + }
> +
> + /* Propagate constants through copy operations and do constant
> + folding. Constants will be substituted to arguments by register
> + allocator where needed and possible. Also detect copies. */
> switch (op) {
> + case INDEX_op_mov_i32:
> +#if TCG_TARGET_REG_BITS == 64
> + case INDEX_op_mov_i64:
> +#endif
> + if ((state[args[1]] == TCG_TEMP_COPY
> + && vals[args[1]] == args[0])
> + || args[0] == args[1]) {
> + args += 2;
> + gen_opc_buf[op_index] = INDEX_op_nop;
> + break;
> + }
> + if (state[args[1]] != TCG_TEMP_CONST) {
> + reset_temp(state, vals, args[0], nb_temps, nb_globals);
> + if (args[1] >= s->nb_globals) {
> + state[args[0]] = TCG_TEMP_COPY;
> + vals[args[0]] = args[1];
> + }
> + gen_args[0] = args[0];
> + gen_args[1] = args[1];
> + gen_args += 2;
> + args += 2;
> + break;
> + } else {
> + /* Source argument is constant. Rewrite the operation and
> + let movi case handle it. */
> + op = mov_to_movi(op);
> + gen_opc_buf[op_index] = op;
> + args[1] = vals[args[1]];
> + /* fallthrough */
> + }
> + case INDEX_op_movi_i32:
> +#if TCG_TARGET_REG_BITS == 64
> + case INDEX_op_movi_i64:
> +#endif
> + reset_temp(state, vals, args[0], nb_temps, nb_globals);
> + state[args[0]] = TCG_TEMP_CONST;
> + vals[args[0]] = args[1];
> + gen_args[0] = args[0];
> + gen_args[1] = args[1];
> + gen_args += 2;
> + args += 2;
> + break;
> case INDEX_op_call:
> case INDEX_op_jmp:
> case INDEX_op_br:
> @@ -55,6 +172,7 @@ static TCGArg *tcg_constant_folding(TCGContext *s,
> uint16_t *tcg_opc_ptr,
> #if TCG_TARGET_REG_BITS == 64
> case INDEX_op_brcond_i64:
> #endif
> + memset(state, 0, nb_temps * sizeof(tcg_temp_state));
> i = (op == INDEX_op_call) ?
> (args[0] >> 16) + (args[0] & 0xffff) + 3 :
> def->nb_args;
> @@ -66,6 +184,11 @@ static TCGArg *tcg_constant_folding(TCGContext *s,
> uint16_t *tcg_opc_ptr,
> }
> break;
> default:
> + /* Default case: we do know nothing about operation so no
> + propagation is done. We only trash output args. */
> + for (i = 0; i < def->nb_oargs; i++) {
> + reset_temp(state, vals, args[i], nb_temps, nb_globals);
> + }
> for (i = 0; i < def->nb_args; i++) {
> gen_args[i] = args[i];
> }
It's not possible to do any optimization across certain ops that have
side effect or helper which access globals directly. For helpers this
can be easily detected looking at the TCG_CALL_PURE and TCG_CALL_CONST
flags. For ops, you should look at TCG_OPF_BB_END, TCG_OPF_CALL_CLOBBER
and TCG_OPF_SIDE_EFFECTS flags.
--
Aurelien Jarno GPG: 1024D/F1BCDB73
aurel...@aurel32.net http://www.aurel32.net
