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tcg/optimize: Optimize sign extensions 

Certain targets, like riscv, produce signed 32-bit results.
This can lead to lots of redundant extensions as values are
manipulated.

Begin by tracking only the obvious sign-extensions, and
converting them to simple copies when possible.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Luis Pires <luis.pires@eldorado.org.br>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Richard Henderson 2021-08-26 12:04:46 -07:00
parent 267c17e825
commit 57fe5c6df2
1 changed files with 102 additions and 21 deletions
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123
tcg/optimize.c
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@ -43,6 +43,7 @@ typedef struct TempOptInfo {
TCGTemp *next_copy;
uint64_t val;
uint64_t z_mask; /* mask bit is 0 if and only if value bit is 0 */
uint64_t s_mask; /* a left-aligned mask of clrsb(value) bits. */
} TempOptInfo;
typedef struct OptContext {
@ -53,9 +54,37 @@ typedef struct OptContext {
/* In flight values from optimization. */
uint64_t a_mask; /* mask bit is 0 iff value identical to first input */
uint64_t z_mask; /* mask bit is 0 iff value bit is 0 */
uint64_t s_mask; /* mask of clrsb(value) bits */
TCGType type;
} OptContext;
/* Calculate the smask for a specific value. */
static uint64_t smask_from_value(uint64_t value)
{
int rep = clrsb64(value);
return ~(~0ull >> rep);
}
/*
* Calculate the smask for a given set of known-zeros.
* If there are lots of zeros on the left, we can consider the remainder
* an unsigned field, and thus the corresponding signed field is one bit
* larger.
*/
static uint64_t smask_from_zmask(uint64_t zmask)
{
/*
* Only the 0 bits are significant for zmask, thus the msb itself
* must be zero, else we have no sign information.
*/
int rep = clz64(zmask);
if (rep == 0) {
return 0;
}
rep -= 1;
return ~(~0ull >> rep);
}
static inline TempOptInfo *ts_info(TCGTemp *ts)
{
return ts->state_ptr;
@ -94,6 +123,7 @@ static void reset_ts(TCGTemp *ts)
ti->prev_copy = ts;
ti->is_const = false;
ti->z_mask = -1;
ti->s_mask = 0;
}
static void reset_temp(TCGArg arg)
@ -124,9 +154,11 @@ static void init_ts_info(OptContext *ctx, TCGTemp *ts)
ti->is_const = true;
ti->val = ts->val;
ti->z_mask = ts->val;
ti->s_mask = smask_from_value(ts->val);
} else {
ti->is_const = false;
ti->z_mask = -1;
ti->s_mask = 0;
}
}
@ -220,6 +252,7 @@ static bool tcg_opt_gen_mov(OptContext *ctx, TCGOp *op, TCGArg dst, TCGArg src)
op->args[1] = src;
di->z_mask = si->z_mask;
di->s_mask = si->s_mask;
if (src_ts->type == dst_ts->type) {
TempOptInfo *ni = ts_info(si->next_copy);
@ -658,13 +691,15 @@ static void finish_folding(OptContext *ctx, TCGOp *op)
nb_oargs = def->nb_oargs;
for (i = 0; i < nb_oargs; i++) {
reset_temp(op->args[i]);
TCGTemp *ts = arg_temp(op->args[i]);
reset_ts(ts);
/*
* Save the corresponding known-zero bits mask for the
* Save the corresponding known-zero/sign bits mask for the
* first output argument (only one supported so far).
*/
if (i == 0) {
arg_info(op->args[i])->z_mask = ctx->z_mask;
ts_info(ts)->z_mask = ctx->z_mask;
ts_info(ts)->s_mask = ctx->s_mask;
}
}
}
@ -714,6 +749,7 @@ static bool fold_masks(OptContext *ctx, TCGOp *op)
{
uint64_t a_mask = ctx->a_mask;
uint64_t z_mask = ctx->z_mask;
uint64_t s_mask = ctx->s_mask;
/*
* 32-bit ops generate 32-bit results, which for the purpose of
@ -725,7 +761,9 @@ static bool fold_masks(OptContext *ctx, TCGOp *op)
if (ctx->type == TCG_TYPE_I32) {
a_mask = (int32_t)a_mask;
z_mask = (int32_t)z_mask;
s_mask |= MAKE_64BIT_MASK(32, 32);
ctx->z_mask = z_mask;
ctx->s_mask = s_mask;
}
if (z_mask == 0) {
@ -1072,7 +1110,7 @@ static bool fold_brcond2(OptContext *ctx, TCGOp *op)
static bool fold_bswap(OptContext *ctx, TCGOp *op)
{
uint64_t z_mask, sign;
uint64_t z_mask, s_mask, sign;
if (arg_is_const(op->args[1])) {
uint64_t t = arg_info(op->args[1])->val;
@ -1082,6 +1120,7 @@ static bool fold_bswap(OptContext *ctx, TCGOp *op)
}
z_mask = arg_info(op->args[1])->z_mask;
switch (op->opc) {
case INDEX_op_bswap16_i32:
case INDEX_op_bswap16_i64:
@ -1100,6 +1139,7 @@ static bool fold_bswap(OptContext *ctx, TCGOp *op)
default:
g_assert_not_reached();
}
s_mask = smask_from_zmask(z_mask);
switch (op->args[2] & (TCG_BSWAP_OZ | TCG_BSWAP_OS)) {
case TCG_BSWAP_OZ:
@ -1108,14 +1148,17 @@ static bool fold_bswap(OptContext *ctx, TCGOp *op)
/* If the sign bit may be 1, force all the bits above to 1. */
if (z_mask & sign) {
z_mask |= sign;
s_mask = sign << 1;
}
break;
default:
/* The high bits are undefined: force all bits above the sign to 1. */
z_mask |= sign << 1;
s_mask = 0;
break;
}
ctx->z_mask = z_mask;
ctx->s_mask = s_mask;
return fold_masks(ctx, op);
}
@ -1263,21 +1306,24 @@ static bool fold_eqv(OptContext *ctx, TCGOp *op)
static bool fold_extract(OptContext *ctx, TCGOp *op)
{
uint64_t z_mask_old, z_mask;
int pos = op->args[2];
int len = op->args[3];
if (arg_is_const(op->args[1])) {
uint64_t t;
t = arg_info(op->args[1])->val;
t = extract64(t, op->args[2], op->args[3]);
t = extract64(t, pos, len);
return tcg_opt_gen_movi(ctx, op, op->args[0], t);
}
z_mask_old = arg_info(op->args[1])->z_mask;
z_mask = extract64(z_mask_old, op->args[2], op->args[3]);
if (op->args[2] == 0) {
z_mask = extract64(z_mask_old, pos, len);
if (pos == 0) {
ctx->a_mask = z_mask_old ^ z_mask;
}
ctx->z_mask = z_mask;
ctx->s_mask = smask_from_zmask(z_mask);
return fold_masks(ctx, op);
}
@ -1303,14 +1349,16 @@ static bool fold_extract2(OptContext *ctx, TCGOp *op)
static bool fold_exts(OptContext *ctx, TCGOp *op)
{
uint64_t z_mask_old, z_mask, sign;
uint64_t s_mask_old, s_mask, z_mask, sign;
bool type_change = false;
if (fold_const1(ctx, op)) {
return true;
}
z_mask_old = z_mask = arg_info(op->args[1])->z_mask;
z_mask = arg_info(op->args[1])->z_mask;
s_mask = arg_info(op->args[1])->s_mask;
s_mask_old = s_mask;
switch (op->opc) {
CASE_OP_32_64(ext8s):
@ -1334,10 +1382,14 @@ static bool fold_exts(OptContext *ctx, TCGOp *op)
if (z_mask & sign) {
z_mask |= sign;
} else if (!type_change) {
ctx->a_mask = z_mask_old ^ z_mask;
}
s_mask |= sign << 1;
ctx->z_mask = z_mask;
ctx->s_mask = s_mask;
if (!type_change) {
ctx->a_mask = s_mask & ~s_mask_old;
}
return fold_masks(ctx, op);
}
@ -1376,6 +1428,7 @@ static bool fold_extu(OptContext *ctx, TCGOp *op)
}
ctx->z_mask = z_mask;
ctx->s_mask = smask_from_zmask(z_mask);
if (!type_change) {
ctx->a_mask = z_mask_old ^ z_mask;
}
@ -1606,8 +1659,12 @@ static bool fold_qemu_ld(OptContext *ctx, TCGOp *op)
MemOp mop = get_memop(oi);
int width = 8 * memop_size(mop);
if (!(mop & MO_SIGN) && width < 64) {
ctx->z_mask = MAKE_64BIT_MASK(0, width);
if (width < 64) {
ctx->s_mask = MAKE_64BIT_MASK(width, 64 - width);
if (!(mop & MO_SIGN)) {
ctx->z_mask = MAKE_64BIT_MASK(0, width);
ctx->s_mask <<= 1;
}
}
/* Opcodes that touch guest memory stop the mb optimization. */
@ -1726,23 +1783,31 @@ static bool fold_setcond2(OptContext *ctx, TCGOp *op)
static bool fold_sextract(OptContext *ctx, TCGOp *op)
{
int64_t z_mask_old, z_mask;
uint64_t z_mask, s_mask, s_mask_old;
int pos = op->args[2];
int len = op->args[3];
if (arg_is_const(op->args[1])) {
uint64_t t;
t = arg_info(op->args[1])->val;
t = sextract64(t, op->args[2], op->args[3]);
t = sextract64(t, pos, len);
return tcg_opt_gen_movi(ctx, op, op->args[0], t);
}
z_mask_old = arg_info(op->args[1])->z_mask;
z_mask = sextract64(z_mask_old, op->args[2], op->args[3]);
if (op->args[2] == 0 && z_mask >= 0) {
ctx->a_mask = z_mask_old ^ z_mask;
}
z_mask = arg_info(op->args[1])->z_mask;
z_mask = sextract64(z_mask, pos, len);
ctx->z_mask = z_mask;
s_mask_old = arg_info(op->args[1])->s_mask;
s_mask = sextract64(s_mask_old, pos, len);
s_mask |= MAKE_64BIT_MASK(len, 64 - len);
ctx->s_mask = s_mask;
if (pos == 0) {
ctx->a_mask = s_mask & ~s_mask_old;
}
return fold_masks(ctx, op);
}
@ -1819,14 +1884,26 @@ static bool fold_tcg_ld(OptContext *ctx, TCGOp *op)
{
/* We can't do any folding with a load, but we can record bits. */
switch (op->opc) {
CASE_OP_32_64(ld8s):
ctx->s_mask = MAKE_64BIT_MASK(8, 56);
break;
CASE_OP_32_64(ld8u):
ctx->z_mask = MAKE_64BIT_MASK(0, 8);
ctx->s_mask = MAKE_64BIT_MASK(9, 55);
break;
CASE_OP_32_64(ld16s):
ctx->s_mask = MAKE_64BIT_MASK(16, 48);
break;
CASE_OP_32_64(ld16u):
ctx->z_mask = MAKE_64BIT_MASK(0, 16);
ctx->s_mask = MAKE_64BIT_MASK(17, 47);
break;
case INDEX_op_ld32s_i64:
ctx->s_mask = MAKE_64BIT_MASK(32, 32);
break;
case INDEX_op_ld32u_i64:
ctx->z_mask = MAKE_64BIT_MASK(0, 32);
ctx->s_mask = MAKE_64BIT_MASK(33, 31);
break;
default:
g_assert_not_reached();
@ -1889,9 +1966,10 @@ void tcg_optimize(TCGContext *s)
ctx.type = TCG_TYPE_I32;
}
/* Assume all bits affected, and no bits known zero. */
/* Assume all bits affected, no bits known zero, no sign reps. */
ctx.a_mask = -1;
ctx.z_mask = -1;
ctx.s_mask = 0;
/*
* Process each opcode.
@ -1964,8 +2042,11 @@ void tcg_optimize(TCGContext *s)
case INDEX_op_extrh_i64_i32:
done = fold_extu(&ctx, op);
break;
CASE_OP_32_64(ld8s):
CASE_OP_32_64(ld8u):
CASE_OP_32_64(ld16s):
CASE_OP_32_64(ld16u):
case INDEX_op_ld32s_i64:
case INDEX_op_ld32u_i64:
done = fold_tcg_ld(&ctx, op);
break;