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glift: Add `-simple-cost-model` option 

Rather than assigning specific weights to specific versions of taint tracking logic and summing the weights of all GLIFT cells, sum the following values for each GLIFT cell:
  - 0 if the associated hole/$anyconst cell value is non-zero, i.e. reduced-precision taint tracking logic is chosen at this cell
  - 1 if the associated hole/$anyconst cell value is zero, i.e. the full-precision taint tracking logic is chosen at this cell

This simplified cost modeling reduces the potential for the QBF-SAT solver to minimize taint tracking logic area but significantly simplifies the QBF-SAT problem.
This commit is contained in:
Alberto Gonzalez 2020-06-13 08:20:01 +00:00
parent c26a8d1ee0
commit 91c20fca72
No known key found for this signature in database
GPG Key ID: 8395A8BA109708B2
1 changed files with 43 additions and 18 deletions
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31
passes/cmds/glift.cc
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@ -28,7 +28,7 @@ struct GliftPass : public Pass {
private:
bool opt_create_precise_model, opt_create_imprecise_model, opt_create_instrumented_model;
bool opt_taintconstants, opt_keepoutputs, opt_nocostmodel, opt_instrumentmore;
bool opt_taintconstants, opt_keepoutputs, opt_simplecostmodel, opt_nocostmodel, opt_instrumentmore;
std::vector<std::string> args;
std::vector<std::string>::size_type argidx;
std::vector<RTLIL::Wire *> new_taint_outputs;
@ -59,6 +59,10 @@ struct GliftPass : public Pass {
opt_keepoutputs = true;
continue;
}
if (args[argidx] == "-simple-cost-model") {
opt_simplecostmodel = true;
continue;
}
if (args[argidx] == "-no-cost-model") {
opt_nocostmodel = true;
continue;
@ -73,6 +77,10 @@ struct GliftPass : public Pass {
log_cmd_error("No command provided. See help for usage.\n");
if(static_cast<int>(opt_create_precise_model) + static_cast<int>(opt_create_imprecise_model) + static_cast<int>(opt_create_instrumented_model) != 1)
log_cmd_error("Only one command may be specified. See help for usage.\n");
if(opt_simplecostmodel && opt_nocostmodel)
log_cmd_error("Only one of `-simple-cost-model` and `-no-cost-model` may be specified. See help for usage.\n");
if((opt_simplecostmodel || opt_nocostmodel) && !opt_create_instrumented_model)
log_cmd_error("Options `-simple-cost-model` and `-no-cost-model` may only be used with `-create-instrumented-model`. See help for usage.\n");
}
RTLIL::SigSpec get_corresponding_taint_signal(RTLIL::SigSpec sig) {
@ -153,6 +161,13 @@ struct GliftPass : public Pass {
RTLIL::SigSpec score_metamux_select(const RTLIL::SigSpec &metamux_select) {
log_assert(metamux_select.is_wire());
if (opt_simplecostmodel) {
//The complex model is an area model, so a lower score should mean smaller.
//In this case, a nonzero hole metamux select value means less logic.
//Thus we should invert the ReduceOr over the metamux_select signal.
RTLIL::SigSpec pmux_select = module->ReduceOr(metamux_select.as_wire()->name.str() + "_nonzero", metamux_select);
return module->Pmux(NEW_ID, RTLIL::Const(1), RTLIL::Const(0), pmux_select, metamux_select.as_wire()->get_src_attribute());
} else {
auto num_versions = opt_instrumentmore? 8 : 4;
auto select_width = log2(num_versions);
log_assert(metamux_select.as_wire()->width == select_width);
@ -173,6 +188,7 @@ struct GliftPass : public Pass {
log_assert(pmux_y_ports.size() == 1);
return pmux_y_ports[0];
}
}
void create_glift_logic() {
std::vector<RTLIL::SigSig> connections(module->connections());
@ -276,7 +292,7 @@ struct GliftPass : public Pass {
new_taint_outputs.push_back(first.as_wire());
} //end foreach conn in connections
//Create a rough model of area by summing the "weight" score of each meta-mux select:
//Create a rough model of area by summing the (potentially simplified) "weight" score of each meta-mux select:
if (!opt_nocostmodel) {
std::vector<RTLIL::SigSpec> meta_mux_select_sums;
std::vector<RTLIL::SigSpec> meta_mux_select_sums_buf;
@ -317,6 +333,7 @@ struct GliftPass : public Pass {
opt_create_instrumented_model = false;
opt_taintconstants = false;
opt_keepoutputs = false;
opt_simplecostmodel = false;
opt_nocostmodel = false;
opt_instrumentmore = false;
module = nullptr;
@ -328,7 +345,7 @@ struct GliftPass : public Pass {
public:
GliftPass() : Pass("glift", "create GLIFT models and optimization problems"), opt_create_precise_model(false), opt_create_imprecise_model(false), opt_create_instrumented_model(false), opt_taintconstants(false), opt_keepoutputs(false), opt_nocostmodel(false), opt_instrumentmore(false), module(nullptr) { }
GliftPass() : Pass("glift", "create GLIFT models and optimization problems"), opt_create_precise_model(false), opt_create_imprecise_model(false), opt_create_instrumented_model(false), opt_taintconstants(false), opt_keepoutputs(false), opt_simplecostmodel(false), opt_nocostmodel(false), opt_instrumentmore(false), module(nullptr) { }
void help() YS_OVERRIDE
{
@ -388,6 +405,14 @@ struct GliftPass : public Pass {
log(" alongside the orignal outputs.\n");
log(" (default: original module outputs are removed)\n");
log("\n");
log(" -simple-cost-model\n");
log(" Do not model logic area. Instead model the number of non-zero assignments to $anyconsts.\n");
log(" Taint tracking logic versions vary in their size, but all reduced-precision versions are\n");
log(" significantly smaller than the fully-precise version. A non-zero $anyconst assignment means\n");
log(" that reduced-precision taint tracking logic was chosen for some gate.\n");
log(" Only applicable in combination with `-create-instrumented-model`.\n");
log(" (default: use a complex model and give that wire the \"keep\" and \"minimize\" attributes)\n");
log("\n");
log(" -no-cost-model\n");
log(" Do not model taint tracking logic area and do not create a `__glift_weight` wire.\n");
log(" Only applicable in combination with `-create-instrumented-model`.\n");