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Fix left shift of unsized constants in sef-determined context. 

When left-shifting unsized constants in self-determined contexts, the
constant value is normally pared down to its minimum required width.
But this practically guarantees loss of bits. Instead, detect this
special case and give the unsized constant a width of an integer.

Still allow for the super-special case that the shifted value and the
shift amount are constants. In that case, the result width (and value)
can be calculated precisely and there is no need to resort to default
widths.
This commit is contained in:
Stephen Williams 2008-04-22 11:23:24 -07:00
parent 5ab0c20a7d
commit a12a6d925a
3 changed files with 63 additions and 13 deletions
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10
PExpr.h
View File

@ -544,7 +544,7 @@ class PEBinary : public PExpr {
const NetExpr* decay,
Link::strength_t drive0,
Link::strength_t drive1) const;
virtual NetEBinary*elaborate_expr(Design*des, NetScope*,
virtual NetExpr*elaborate_expr(Design*des, NetScope*,
int expr_width, bool sys_task_arg) const;
virtual NetExpr*elaborate_pexpr(Design*des, NetScope*sc) const;
virtual verinum* eval_const(Design*des, NetScope*sc) const;
@ -554,8 +554,8 @@ class PEBinary : public PExpr {
PExpr*left_;
PExpr*right_;
NetEBinary*elaborate_expr_base_(Design*, NetExpr*lp, NetExpr*rp, int use_wid) const;
NetEBinary*elaborate_eval_expr_base_(Design*, NetExpr*lp, NetExpr*rp, int use_wid) const;
NetExpr*elaborate_expr_base_(Design*, NetExpr*lp, NetExpr*rp, int use_wid) const;
NetExpr*elaborate_eval_expr_base_(Design*, NetExpr*lp, NetExpr*rp, int use_wid) const;
static void suppress_operand_sign_if_needed_(NetExpr*lp, NetExpr*rp);
@ -621,8 +621,8 @@ class PEBComp : public PEBinary {
unsigned min, unsigned lval,
bool&flag) const;
NetEBinary* elaborate_expr(Design*des, NetScope*scope,
int expr_width, bool sys_task_arg) const;
NetExpr* elaborate_expr(Design*des, NetScope*scope,
int expr_width, bool sys_task_arg) const;
};
class PEBShift : public PEBinary {

64
elab_expr.cc
View File

@ -96,7 +96,7 @@ unsigned PEBinary::test_width(Design*des, NetScope*scope,
* and right sides, and creating one of a variety of different NetExpr
* types.
*/
NetEBinary* PEBinary::elaborate_expr(Design*des, NetScope*scope,
NetExpr* PEBinary::elaborate_expr(Design*des, NetScope*scope,
int expr_wid, bool) const
{
assert(left_);
@ -110,7 +110,7 @@ NetEBinary* PEBinary::elaborate_expr(Design*des, NetScope*scope,
return 0;
}
NetEBinary*tmp = elaborate_eval_expr_base_(des, lp, rp, expr_wid);
NetExpr*tmp = elaborate_eval_expr_base_(des, lp, rp, expr_wid);
return tmp;
}
@ -128,7 +128,7 @@ void PEBinary::suppress_operand_sign_if_needed_(NetExpr*lp, NetExpr*rp)
lp->cast_signed(false);
}
NetEBinary* PEBinary::elaborate_eval_expr_base_(Design*des,
NetExpr* PEBinary::elaborate_eval_expr_base_(Design*des,
NetExpr*lp,
NetExpr*rp,
int expr_wid) const
@ -146,7 +146,7 @@ NetEBinary* PEBinary::elaborate_eval_expr_base_(Design*des,
* operands are elaborated as necessary, and all I need to do is make
* the correct NetEBinary object and connect the parameters.
*/
NetEBinary* PEBinary::elaborate_expr_base_(Design*des,
NetExpr* PEBinary::elaborate_expr_base_(Design*des,
NetExpr*lp, NetExpr*rp,
int expr_wid) const
{
@ -157,7 +157,7 @@ NetEBinary* PEBinary::elaborate_expr_base_(Design*des,
<< *this << " expr_wid=" << expr_wid << endl;
}
NetEBinary*tmp;
NetExpr*tmp;
switch (op_) {
default:
@ -200,6 +200,56 @@ NetEBinary* PEBinary::elaborate_expr_base_(Design*des,
break;
case 'l': // <<
if (NetEConst*lpc = dynamic_cast<NetEConst*> (lp)) {
if (NetEConst*rpc = dynamic_cast<NetEConst*> (rp)) {
// Handle the super-special case that both
// operands are constants. Precalculate the
// entire value here.
verinum lpval = lpc->value();
unsigned shift = rpc->value().as_ulong();
verinum result = lpc->value() << shift;
// If the l-value has explicit size, or
// there is a context determined size, use that.
if (lpval.has_len() || expr_wid > 0) {
int use_len = lpval.len();
if (expr_wid < use_len)
use_len = expr_wid;
result = verinum(result, lpval.len());
}
tmp = new NetEConst(result);
if (debug_elaborate)
cerr << get_fileline() << ": debug: "
<< "Precalculate " << *this
<< " to constant " << *tmp << endl;
} else {
// Handle the special case that the left
// operand is constant. If it is unsized, we
// may have to expand it to an integer width.
verinum lpval = lpc->value();
if (lpval.len() < integer_width && !lpval.has_len()) {
lpval = verinum(lpval, integer_width);
lpc = new NetEConst(lpval);
lpc->set_line(*lp);
}
tmp = new NetEBShift(op_, lpc, rp);
if (debug_elaborate)
cerr << get_fileline() << ": debug: "
<< "Adjust " << *this
<< " to this " << *tmp
<< " to allow for integer widths." << endl;
}
} else {
// Left side is not constant, so handle it the
// default way.
tmp = new NetEBShift(op_, lp, rp);
}
tmp->set_line(*this);
break;
case 'r': // >>
case 'R': // >>>
tmp = new NetEBShift(op_, lp, rp);
@ -269,8 +319,8 @@ unsigned PEBComp::test_width(Design*, NetScope*,unsigned, unsigned, bool&) const
return 1;
}
NetEBinary* PEBComp::elaborate_expr(Design*des, NetScope*scope,
int expr_width, bool sys_task_arg) const
NetExpr* PEBComp::elaborate_expr(Design*des, NetScope*scope,
int expr_width, bool sys_task_arg) const
{
assert(left_);
assert(right_);

2
elab_pexpr.cc
View File

@ -53,7 +53,7 @@ NetExpr*PEBinary::elaborate_pexpr (Design*des, NetScope*scope) const
return 0;
}
NetEBinary*tmp = elaborate_expr_base_(des, lp, rp, -2);
NetExpr*tmp = elaborate_expr_base_(des, lp, rp, -2);
return tmp;
}