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Make the associative sum constant elimination more resilient to size details. 

The NetEBAdd::eval_tree method is able to use the associative property
of addition to reduce some constants, but it is picky about widths.
Make it a little bit more resilient to expression widths.
This commit is contained in:
Stephen Williams 2008-11-12 20:59:10 -08:00
parent 7c50c9aedf
commit 9f2b5cd9b7
1 changed files with 15 additions and 2 deletions
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17
eval_tree.cc
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@ -133,7 +133,18 @@ NetExpr* NetEBAdd::eval_tree(int prune_to_width)
verinum lval = lc->value();
verinum rval = rc->value();
ivl_assert(*this, se->expr_width() == this->expr_width());
if (lval.len() < expr_width())
lval = pad_to_width(lval, expr_width());
if (rval.len() < expr_width())
rval = pad_to_width(rval, expr_width());
if (se->expr_width() > this->expr_width()) {
cerr << get_fileline() << ": internal error: "
<< "expr_width()=" << expr_width()
<< ", sub expr_width()=" << se->expr_width()
<< ", sub expression=" << *se << endl;
}
ivl_assert(*this, se->expr_width() <= this->expr_width());
verinum val;
if (op_ == se->op_) {
@ -146,7 +157,9 @@ NetExpr* NetEBAdd::eval_tree(int prune_to_width)
val = rval - lval;
}
val = pad_to_width(val, expr_width());
// Since we padded the operands above to be the minimum
// width, the val should also be at least expr_width().
ivl_assert(*this, val.len() >= expr_width());
if (val.len() > expr_width()) {
verinum tmp (val, expr_width());
tmp.has_sign(val.has_sign());