mirrors/yosys
3
0
Fork 0
mirror of https://github.com/YosysHQ/yosys synced 2025-08-07 19:51:23 +00:00
Code Activity

peepopt: limit padding from shiftadd

Browse source 
The input to a shift operation is padded.
This reduced the final number of MUX cells
but during techmap it can create huge
temporary multiplexers in the log shifter.
This significantly increases runtime and resources.

A limit is added with a warning when it is used.
This commit is contained in:
Philippe Sauter 2024-06-14 15:30:03 +02:00
parent 62bff3a204
commit 2f0f10cb87
2 changed files with 23 additions and 3 deletions
Download patch file Download diff file Expand all files Collapse all files

11
passes/pmgen/peepopt.cc
View file

@ -25,6 +25,9 @@ PRIVATE_NAMESPACE_BEGIN
bool did_something;
// scratchpad configurations for pmgen
int shiftadd_max_ratio;
#include "passes/pmgen/peepopt_pm.h"
struct PeepoptPass : public Pass {
@ -50,6 +53,9 @@ struct PeepoptPass : public Pass {
log("\n");
log(" * shiftadd - Replace A>>(B+D) with (A'>>D)>>(B) where D is constant and\n");
log(" A' is derived from A by padding or cutting inaccessible bits.\n");
log(" Scratchpad: 'peepopt.shiftadd.max_data_multiple' (default: 2)\n");
log(" limits the amount of padding to a multiple of the data, \n");
log(" to avoid high resource usage from large temporary MUX trees.\n");
log("\n");
}
void execute(std::vector<std::string> args, RTLIL::Design *design) override
@ -63,6 +69,11 @@ struct PeepoptPass : public Pass {
}
extra_args(args, argidx, design);
// limit the padding from shiftadd to a multiple of the input data
// during techmap it creates (#data + #padding) * log(shift) $_MUX_ cells
// 2x implies there is a constant shift larger than the input-data which should be extremely rare
shiftadd_max_ratio = design->scratchpad_get_int("peepopt.shiftadd.max_data_multiple", 2);
for (auto module : design->selected_modules())
{
did_something = true;