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verilog: support recursive functions using ternary expressions

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This adds a mechanism for marking certain portions of elaboration as
occurring within unevaluated ternary branches. To enable elaboration of
the overall ternary, this also adds width detection for these
unelaborated function calls.
This commit is contained in:
Zachary Snow 2021-02-12 14:25:34 -05:00
parent 9f7cd10c98
commit 8de2e863af
5 changed files with 195 additions and 19 deletions
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100
frontends/ast/simplify.cc
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@ -575,6 +575,8 @@ bool AstNode::simplify(bool const_fold, bool at_zero, bool in_lvalue, int stage,
deep_recursion_warning = false;
}
static bool unevaluated_tern_branch = false;
AstNode *newNode = NULL;
bool did_something = false;
@ -1091,7 +1093,6 @@ bool AstNode::simplify(bool const_fold, bool at_zero, bool in_lvalue, int stage,
break;
case AST_TERNARY:
detect_width_simple = true;
child_0_is_self_determined = true;
break;
@ -1124,6 +1125,24 @@ bool AstNode::simplify(bool const_fold, bool at_zero, bool in_lvalue, int stage,
detectSignWidth(width_hint, sign_hint);
if (type == AST_TERNARY) {
if (width_hint < 0) {
while (!children[0]->basic_prep && children[0]->simplify(true, false, in_lvalue, stage, -1, false, in_param))
did_something = true;
bool backup_unevaluated_tern_branch = unevaluated_tern_branch;
AstNode *chosen = get_tern_choice().first;
unevaluated_tern_branch = backup_unevaluated_tern_branch || chosen == children[2];
while (!children[1]->basic_prep && children[1]->simplify(false, false, in_lvalue, stage, -1, false, in_param))
did_something = true;
unevaluated_tern_branch = backup_unevaluated_tern_branch || chosen == children[1];
while (!children[2]->basic_prep && children[2]->simplify(false, false, in_lvalue, stage, -1, false, in_param))
did_something = true;
unevaluated_tern_branch = backup_unevaluated_tern_branch;
detectSignWidth(width_hint, sign_hint);
}
int width_hint_left, width_hint_right;
bool sign_hint_left, sign_hint_right;
bool found_real_left, found_real_right;
@ -1187,6 +1206,7 @@ bool AstNode::simplify(bool const_fold, bool at_zero, bool in_lvalue, int stage,
for (size_t i = 0; i < children.size(); i++) {
bool did_something_here = true;
bool backup_flag_autowire = flag_autowire;
bool backup_unevaluated_tern_branch = unevaluated_tern_branch;
if ((type == AST_GENFOR || type == AST_FOR) && i >= 3)
break;
if ((type == AST_GENIF || type == AST_GENCASE) && i >= 1)
@ -1199,6 +1219,10 @@ bool AstNode::simplify(bool const_fold, bool at_zero, bool in_lvalue, int stage,
break;
if (type == AST_DEFPARAM && i == 0)
flag_autowire = true;
if (type == AST_TERNARY && i > 0 && !unevaluated_tern_branch) {
AstNode *chosen = get_tern_choice().first;
unevaluated_tern_branch = chosen && chosen != children[i];
}
while (did_something_here && i < children.size()) {
bool const_fold_here = const_fold, in_lvalue_here = in_lvalue;
int width_hint_here = width_hint;
@ -1238,6 +1262,7 @@ bool AstNode::simplify(bool const_fold, bool at_zero, bool in_lvalue, int stage,
did_something = true;
}
flag_autowire = backup_flag_autowire;
unevaluated_tern_branch = backup_unevaluated_tern_branch;
}
for (auto &attr : attributes) {
while (attr.second->simplify(true, false, false, stage, -1, false, true))
@ -3177,6 +3202,8 @@ skip_dynamic_range_lvalue_expansion:;
std::string prefix = sstr.str();
AstNode *decl = current_scope[str];
if (unevaluated_tern_branch && decl->is_recursive_function())
goto replace_fcall_later;
decl = decl->clone();
decl->replace_result_wire_name_in_function(str, "$result"); // enables recursion
decl->expand_genblock(prefix);
@ -3610,24 +3637,9 @@ replace_fcall_later:;
case AST_TERNARY:
if (children[0]->isConst())
{
bool found_sure_true = false;
bool found_maybe_true = false;
if (children[0]->type == AST_CONSTANT)
for (auto &bit : children[0]->bits) {
if (bit == RTLIL::State::S1)
found_sure_true = true;
if (bit > RTLIL::State::S1)
found_maybe_true = true;
}
else
found_sure_true = children[0]->asReal(sign_hint) != 0;
AstNode *choice = NULL, *not_choice = NULL;
if (found_sure_true)
choice = children[1], not_choice = children[2];
else if (!found_maybe_true)
choice = children[2], not_choice = children[1];
auto pair = get_tern_choice();
AstNode *choice = pair.first;
AstNode *not_choice = pair.second;
if (choice != NULL) {
if (choice->type == AST_CONSTANT) {
@ -4845,4 +4857,54 @@ void AstNode::allocateDefaultEnumValues()
}
}
bool AstNode::is_recursive_function() const
{
std::set<const AstNode *> visited;
std::function<bool(const AstNode *node)> visit = [&](const AstNode *node) {
if (visited.count(node))
return node == this;
visited.insert(node);
if (node->type == AST_FCALL) {
auto it = current_scope.find(node->str);
if (it != current_scope.end() && visit(it->second))
return true;
}
for (const AstNode *child : node->children) {
if (visit(child))
return true;
}
return false;
};
log_assert(type == AST_FUNCTION);
return visit(this);
}
std::pair<AstNode*, AstNode*> AstNode::get_tern_choice()
{
if (!children[0]->isConst())
return {};
bool found_sure_true = false;
bool found_maybe_true = false;
if (children[0]->type == AST_CONSTANT)
for (auto &bit : children[0]->bits) {
if (bit == RTLIL::State::S1)
found_sure_true = true;
if (bit > RTLIL::State::S1)
found_maybe_true = true;
}
else
found_sure_true = children[0]->asReal(true) != 0;
AstNode *choice = nullptr, *not_choice = nullptr;
if (found_sure_true)
choice = children[1], not_choice = children[2];
else if (!found_maybe_true)
choice = children[2], not_choice = children[1];
return {choice, not_choice};
}
YOSYS_NAMESPACE_END