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Improved rewrite code for writing to bit slice (disabled for now) 

This adds the new rewrite rule. But it's still missing a check that makes
sure the new rewrite rule is actually a valid substitute in the always
block being processed. Therefore the new rewrite rule is just disabled
for now.

Signed-off-by: Claire Wolf <claire@symbioticeda.com>
This commit is contained in:
Claire Wolf 2020-04-01 12:43:42 +02:00
parent 3c4758c60e
commit 4711fea6c0
1 changed files with 64 additions and 12 deletions
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76
frontends/ast/simplify.cc
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@ -1721,8 +1721,10 @@ bool AstNode::simplify(bool const_fold, bool at_zero, bool in_lvalue, int stage,
}
// replace dynamic ranges in left-hand side expressions (e.g. "foo[bar] <= 1'b1;") with
// a big case block that selects the correct single-bit assignment.
if (type == AST_ASSIGN_EQ || type == AST_ASSIGN_LE) {
// either a big case block that selects the correct single-bit assignment, or mask and
// shift operations.
if (type == AST_ASSIGN_EQ || type == AST_ASSIGN_LE)
{
if (children[0]->type != AST_IDENTIFIER || children[0]->children.size() == 0)
goto skip_dynamic_range_lvalue_expansion;
if (children[0]->children[0]->range_valid || did_something)
@ -1731,10 +1733,13 @@ bool AstNode::simplify(bool const_fold, bool at_zero, bool in_lvalue, int stage,
goto skip_dynamic_range_lvalue_expansion;
if (!children[0]->id2ast->range_valid)
goto skip_dynamic_range_lvalue_expansion;
int source_width = children[0]->id2ast->range_left - children[0]->id2ast->range_right + 1;
int result_width = 1;
AstNode *shift_expr = NULL;
AstNode *range = children[0]->children[0];
if (range->children.size() == 1) {
shift_expr = range->children[0]->clone();
} else {
@ -1747,19 +1752,66 @@ bool AstNode::simplify(bool const_fold, bool at_zero, bool in_lvalue, int stage,
log_file_error(filename, location.first_line, "Unsupported expression on dynamic range select on signal `%s'!\n", str.c_str());
result_width = abs(int(left_at_zero_ast->integer - right_at_zero_ast->integer)) + 1;
}
did_something = true;
newNode = new AstNode(AST_CASE, shift_expr);
for (int i = 0; i < source_width; i++) {
int start_bit = children[0]->id2ast->range_right + i;
AstNode *cond = new AstNode(AST_COND, mkconst_int(start_bit, true));
if (1)
{
// big case block
did_something = true;
newNode = new AstNode(AST_CASE, shift_expr);
for (int i = 0; i < source_width; i++) {
int start_bit = children[0]->id2ast->range_right + i;
AstNode *cond = new AstNode(AST_COND, mkconst_int(start_bit, true));
AstNode *lvalue = children[0]->clone();
lvalue->delete_children();
int end_bit = std::min(start_bit+result_width,source_width) - 1;
lvalue->children.push_back(new AstNode(AST_RANGE,
mkconst_int(end_bit, true), mkconst_int(start_bit, true)));
cond->children.push_back(new AstNode(AST_BLOCK, new AstNode(type, lvalue, children[1]->clone())));
newNode->children.push_back(cond);
}
}
else
{
// mask and shift operations, disabled for now
AstNode *wire_mask = new AstNode(AST_WIRE, new AstNode(AST_RANGE, mkconst_int(source_width-1, true), mkconst_int(0, true)));
wire_mask->str = stringf("$bitselwrite$mask$%s:%d$%d", filename.c_str(), location.first_line, autoidx++);
wire_mask->attributes["\\nosync"] = AstNode::mkconst_int(1, false);
wire_mask->is_logic = true;
while (wire_mask->simplify(true, false, false, 1, -1, false, false)) { }
current_ast_mod->children.push_back(wire_mask);
AstNode *wire_data = new AstNode(AST_WIRE, new AstNode(AST_RANGE, mkconst_int(source_width-1, true), mkconst_int(0, true)));
wire_data->str = stringf("$bitselwrite$data$%s:%d$%d", filename.c_str(), location.first_line, autoidx++);
wire_data->attributes["\\nosync"] = AstNode::mkconst_int(1, false);
wire_data->is_logic = true;
while (wire_data->simplify(true, false, false, 1, -1, false, false)) { }
current_ast_mod->children.push_back(wire_data);
did_something = true;
newNode = new AstNode(AST_BLOCK);
AstNode *lvalue = children[0]->clone();
lvalue->delete_children();
int end_bit = std::min(start_bit+result_width,source_width) - 1;
lvalue->children.push_back(new AstNode(AST_RANGE,
mkconst_int(end_bit, true), mkconst_int(start_bit, true)));
cond->children.push_back(new AstNode(AST_BLOCK, new AstNode(type, lvalue, children[1]->clone())));
newNode->children.push_back(cond);
AstNode *ref_mask = new AstNode(AST_IDENTIFIER);
ref_mask->str = wire_mask->str;
ref_mask->was_checked = true;
AstNode *ref_data = new AstNode(AST_IDENTIFIER);
ref_data->str = wire_data->str;
ref_data->was_checked = true;
AstNode *shamt = shift_expr;
newNode->children.push_back(new AstNode(AST_ASSIGN_EQ, ref_mask->clone(),
new AstNode(AST_SHIFT_LEFT, mkconst_bits(std::vector<RTLIL::State>(result_width, State::S1), false), shamt->clone())));
newNode->children.push_back(new AstNode(AST_ASSIGN_EQ, ref_data->clone(),
new AstNode(AST_SHIFT_LEFT, new AstNode(AST_BIT_AND, mkconst_bits(std::vector<RTLIL::State>(result_width, State::S1), false), children[1]->clone()), shamt)));
newNode->children.push_back(new AstNode(type, lvalue, new AstNode(AST_BIT_OR, new AstNode(AST_BIT_AND, lvalue->clone(), new AstNode(AST_BIT_NOT, ref_mask)), ref_data)));
}
goto apply_newNode;
}
skip_dynamic_range_lvalue_expansion:;