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Add a warning if an expression pads itself to a crazy width.

This commit is contained in:
Stephen Williams 2014-11-25 14:49:04 -08:00
parent 679021a1b5
commit 82ca4cf641
1 changed files with 53 additions and 2 deletions
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55
elab_expr.cc
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@ -266,6 +266,13 @@ unsigned PEBinary::test_width(Design*des, NetScope*scope, width_mode_t&mode)
unsigned l_width = left_->test_width(des, scope, mode);
if (debug_elaborate) {
cerr << get_fileline() << ": PEBinary::test_width: "
<< "op_=" << op_ << ", l_width=" << l_width
<< ", r_width=" << r_width
<< ", saved_mode=" << saved_mode << endl;
}
// If the width mode changed, retest the right operand, as it
// may choose a different width if it is in a lossless context.
if ((mode >= LOSSLESS) && (saved_mode < LOSSLESS))
@ -716,6 +723,14 @@ unsigned PEBLeftWidth::test_width(Design*des, NetScope*scope, width_mode_t&mode)
ivl_assert(*this, left_);
ivl_assert(*this, right_);
if (debug_elaborate) {
cerr << get_fileline() << ": PEBLeftWidth::test_width: "
<< "op_=" << op_
<< ", left_=" << *left_
<< ", right_=" << *right_
<< ", mode=" << width_mode_name(mode) << endl;
}
// The right operand is self determined. Test its type and
// width for use later. We only need to know its width now
// if the left operand is unsized and we need to calculate
@ -723,11 +738,26 @@ unsigned PEBLeftWidth::test_width(Design*des, NetScope*scope, width_mode_t&mode)
width_mode_t r_mode = SIZED;
unsigned r_width = right_->test_width(des, scope, r_mode);
expr_width_ = left_->test_width(des, scope, mode);
// The left operand is what will determine the size of the
// expression. The l_mode will be converted to UNSIZED if the
// expression does not have a well-determined size.
width_mode_t l_mode = SIZED;
expr_width_ = left_->test_width(des, scope, l_mode);
expr_type_ = left_->expr_type();
signed_flag_ = left_->has_sign();
if (mode==SIZED)
mode = l_mode;
// The left operand width defines the size of the
// expression. If the expression has a well-defined size, the
// left_->test_width() above would have set mode==SIZED and we
// can skip a lot of stuff. But if the mode is an undetermined
// size, we need to figure out what we really want to keep a
// lossless value. That's what the following if(...) {...} is
// all about.
if ((mode >= EXPAND) && type_is_vectorable(expr_type_)) {
// We need to make our best guess at the right operand
// value, to minimize the calculated width. This is
// particularly important for the power operator...
@ -757,6 +787,13 @@ unsigned PEBLeftWidth::test_width(Design*des, NetScope*scope, width_mode_t&mode)
if (rc && (r_width < sizeof(long)*8))
r_val = rc->value().as_long();
if (debug_elaborate && rc) {
cerr << get_fileline() << ": PEBLeftWidth::test_width: "
<< "Evaluated rc=" << *rc
<< ", r_val=" << r_val
<< ", width_cap=" << width_cap << endl;
}
// Clip to a sensible range to avoid underflow/overflow
// in the following calculations.
if (r_val < 0)
@ -773,7 +810,8 @@ unsigned PEBLeftWidth::test_width(Design*des, NetScope*scope, width_mode_t&mode)
unsigned use_width = expr_width_;
switch (op_) {
case 'l': // <<
use_width += (unsigned)r_val;
if (l_mode != SIZED)
use_width += (unsigned)r_val;
break;
case 'r': // >>
@ -811,6 +849,12 @@ unsigned PEBLeftWidth::test_width(Design*des, NetScope*scope, width_mode_t&mode)
if ((rc == 0) && (use_width > expr_width_) && (use_width > integer_width))
use_width = integer_width;
if (use_width >= width_cap) {
cerr << get_fileline() << ": warning: "
<< "Unsized expression (" << *this << ")"
<< " expanded beyond and was clipped to " << use_width
<< " bits. Try using sized operands." << endl;
}
expr_width_ = use_width;
}
@ -819,6 +863,13 @@ unsigned PEBLeftWidth::test_width(Design*des, NetScope*scope, width_mode_t&mode)
else
min_width_ = UINT_MAX; // disable width pruning
if (debug_elaborate) {
cerr << get_fileline() << ": PEBLeftWidth::test_width: "
<< "Done calculating expr_width_=" << expr_width_
<< ", min_width_=" << min_width_
<< ", mode=" << width_mode_name(mode) << endl;
}
return fix_width_(mode);
}