luke
/
iverilog
mirror of https://github.com/steveicarus/iverilog.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

Support drawing some select expressions in place. 

Select of signals is natural for evaluating in place, if possible.
Doing so can save instructions for certain expressions.
This commit is contained in:
Stephen Williams 2008-11-22 21:17:05 -08:00
parent 83a7497912
commit 4de891d096
1 changed files with 106 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

116
tgt-vvp/eval_expr.c
View File

@ -1803,6 +1803,25 @@ static struct vector_info draw_number_expr(ivl_expr_t exp, unsigned wid)
return res;
}
/*
* This little helper function generates the instructions to pad a
* vector in place. It is assumed that the calling functio has set up
* the first sub_sidth bits of the dest vector, and the signed_flag is
* true if the extension is to be signed.
*/
static void pad_in_place(struct vector_info dest, unsigned sub_width, int signed_flag)
{
if (signed_flag) {
unsigned idx;
for (idx = sub_width ; idx < dest.wid ; idx += 1)
fprintf(vvp_out, " %%mov %u, %u, 1;\n",
dest.base+idx, dest.base+sub_width-1);
} else {
fprintf(vvp_out, " %%mov %u, 0, %u;\n",
dest.base+sub_width, dest.wid - sub_width);
}
}
/*
* The PAD expression takes a smaller node and pads it out to a larger
* value. It will zero extend or sign extend depending on the
@ -1848,16 +1867,8 @@ static struct vector_info draw_pad_expr(ivl_expr_t exp, unsigned wid)
subv.wid = ivl_expr_width(subexpr);
draw_eval_expr_dest(subexpr, subv, 0);
if (ivl_expr_signed(exp)) {
unsigned idx;
for (idx = subv.wid ; idx < res.wid ; idx += 1)
fprintf(vvp_out, " %%mov %u, %u, 1;\n",
res.base+idx, subv.base+subv.wid-1);
} else {
fprintf(vvp_out, " %%mov %u, 0, %u;\n",
res.base+subv.wid, res.wid - subv.wid);
}
pad_in_place(res, subv.wid, ivl_expr_signed(exp));
save_expression_lookaside(res.base, exp, wid);
return res;
}
@ -2261,6 +2272,43 @@ static struct vector_info draw_select_signal(ivl_expr_t sube,
return res;
}
static void draw_select_signal_dest(ivl_expr_t sube,
ivl_expr_t bit_idx,
struct vector_info dest,
int stuff_ok_flag)
{
struct vector_info tmp;
ivl_signal_t sig = ivl_expr_signal(sube);
/* Special case: If the operand is a signal (not an array) and
the part select is coming from the LSB, and the part select
is no larger then the signal itself, then we can load the
value in place, directly. */
if ((ivl_signal_dimensions(sig) == 0)
&& (ivl_expr_width(sube) >= dest.wid)
&& number_is_immediate(bit_idx, 32, 0)
&& get_number_immediate(bit_idx) == 0) {
unsigned use_word = 0;
fprintf(vvp_out, " %%load/v %u, v%p_%u, %u; Select %u out of %u bits\n",
dest.base, sig, use_word, dest.wid,
dest.wid, ivl_expr_width(sube));
return;
}
/* Fallback, just draw the expression and copy the result into
the destination. */
tmp = draw_select_signal(sube, bit_idx, dest.wid, dest.wid);
assert(tmp.wid == dest.wid);
fprintf(vvp_out, " %%mov %u, %u, %u; Move signal select into place\n",
dest.base, tmp.base, dest.wid);
if (tmp.base >= 8) {
save_expression_lookaside(tmp.base, sube, tmp.wid);
clr_vector(tmp);
}
}
static struct vector_info draw_select_expr(ivl_expr_t exp, unsigned wid,
int stuff_ok_flag)
{
@ -2350,6 +2398,50 @@ static struct vector_info draw_select_expr(ivl_expr_t exp, unsigned wid,
return res;
}
static void draw_select_expr_dest(ivl_expr_t exp, struct vector_info dest,
int stuff_ok_flag)
{
struct vector_info tmp;
ivl_expr_t sube = ivl_expr_oper1(exp);
ivl_expr_t shift= ivl_expr_oper2(exp);
/* If the shift expression is not present, then this is really
a pad expression, and that can be handled pretty
easily. Evalutate the subexpression into the destination,
then pad in place. */
if (shift == 0) {
struct vector_info subv;
subv.base = dest.base;
subv.wid = ivl_expr_width(sube);
if (subv.wid > dest.wid)
subv.wid = dest.wid;
draw_eval_expr_dest(sube, subv, stuff_ok_flag);
pad_in_place(dest, subv.wid, ivl_expr_signed(exp));
return;
}
if (ivl_expr_type(sube) == IVL_EX_SIGNAL) {
draw_select_signal_dest(sube, shift, dest, stuff_ok_flag);
return;
}
/* Fallback, is to draw the expression by width, and mov it to
the required dest. */
tmp = draw_select_expr(exp, dest.wid, stuff_ok_flag);
assert(tmp.wid == dest.wid);
fprintf(vvp_out, " %%mov %u, %u, %u; Move select into place\n",
dest.base, tmp.base, dest.wid);
if (tmp.base >= 8) {
save_expression_lookaside(tmp.base, exp, tmp.wid);
clr_vector(tmp);
}
}
static struct vector_info draw_ternary_expr(ivl_expr_t exp, unsigned wid)
{
struct vector_info res, tru, fal, tst;
@ -2690,6 +2782,10 @@ static void draw_eval_expr_dest(ivl_expr_t exp, struct vector_info dest,
draw_signal_dest(exp, dest, -1, 0L);
return;
case IVL_EX_SELECT:
draw_select_expr_dest(exp, dest, stuff_ok_flag);
return;
default:
break;
}