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tgt-vvp: Fix store skip for assignment operator on dynamic part select 

The operator assignment on dynamic part selects uses the `%store/vec4`
instruction to store the value. This instruction will skip the assignment
if flag 4 is set. This is for handling the case where the index is
undefined.

Since the left hand side of the assignment is an arbitrary expression it
can change the flag. The implementation handles this by making a copy of
the flag and restoring it before executing the `%store/vec4` instruction.

The flag is set by the `%ix/vec4` instruction when loading the index
register. But the copy of the flag is made before that and just picks
up the flag that was stored by previous expressions. This can cause
the store to be skipped when it shouldn't.

E.g. in the following code the increment will be skipped. Flag 4 is used
from the `a == 0` comparison, rather than from computing the part select
index.

```
int a = 0;
if (a == 0) begin
  a[a+:2] += 1;
end
$display(a); // Will print 0, should print 1
```

Fix this by moving the copy of the flag after the `%ix/vec4` instruction.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
This commit is contained in:
Lars-Peter Clausen 2022-01-01 10:45:52 +01:00
parent 2abfef68ff
commit e263d5b268
1 changed files with 1 additions and 1 deletions
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2
tgt-vvp/stmt_assign.c
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@ -147,9 +147,9 @@ static void get_vec_from_lval_slice(ivl_lval_t lval, struct vec_slice_info*slice
fprintf(vvp_out, " %%load/vec4 v%p_%lu;\n", sig, use_word);
draw_eval_vec4(part_off_ex);
fprintf(vvp_out, " %%flag_mov %u, 4;\n", slice->u_.part_select_dynamic.x_flag);
fprintf(vvp_out, " %%dup/vec4;\n");
fprintf(vvp_out, " %%ix/vec4 %d;\n", slice->u_.part_select_dynamic.word_idx_reg);
fprintf(vvp_out, " %%flag_mov %u, 4;\n", slice->u_.part_select_dynamic.x_flag);
fprintf(vvp_out, " %%part/u %u;\n", wid);
} else if (ivl_signal_dimensions(sig) > 0 && word_ix == 0) {