From 0d30a4d479b4c5ac931610d019b053815e943cca Mon Sep 17 00:00:00 2001 From: Jannis Harder Date: Mon, 22 Apr 2024 13:26:17 +0200 Subject: [PATCH] rtlil: Add packed `extract` implementation for `SigSpec` Previously `extract` on a `SigSpec` would always unpack it. Since a significant amount of `SigSpec`s have one or few chunks, it's worth having a dedicated implementation. This is especially true, since the RTLIL frontend calls into this for every `wire [lhs:rhs]` slice, making this `extract` take up 40% when profiling `read_rtlil` with one of the largest coarse grained RTLIL designs I had on hand. With this change the `read_rtlil` profile looks like I would expect it to look like, but I noticed that a lot of the other core RTLIL methods also are a bit too eager with unpacking or implementing `SigChunk`/`Const` overloads that just convert to a single chunk `SigSpec` and forward to the implementation for that, when a direct implementation would avoid temporary std::vector allocations. While not relevant for `read_rtlil`, to me it looks like there might be a few easy overall performance gains to be had by addressing this more generally. --- kernel/rtlil.cc | 33 ++++++++++++++++++++++++++++++++- 1 file changed, 32 insertions(+), 1 deletion(-) diff --git a/kernel/rtlil.cc b/kernel/rtlil.cc index 8781b6a8946..bafafb57b9b 100644 --- a/kernel/rtlil.cc +++ b/kernel/rtlil.cc @@ -4435,8 +4435,39 @@ RTLIL::SigSpec RTLIL::SigSpec::extract(int offset, int length) const log_assert(offset >= 0); log_assert(length >= 0); log_assert(offset + length <= width_); - unpack(); + cover("kernel.rtlil.sigspec.extract_pos"); + + if (packed()) + { + if (chunks_.size() == 1) + return chunks_[0].extract(offset, length); + + SigSpec extracted; + int end = offset + length; + int chunk_end = 0; + + for (auto const &chunk : chunks_) + { + int chunk_begin = chunk_end; + chunk_end += chunk.width; + int extract_begin = std::max(chunk_begin, offset); + int extract_end = std::min(chunk_end, end); + if (extract_begin >= extract_end) + continue; + int extract_offset = extract_begin - chunk_begin; + int extract_len = extract_end - extract_begin; + if (extract_offset == 0 && extract_len == chunk.width) + extracted.chunks_.emplace_back(chunk); + else + extracted.chunks_.emplace_back( + chunk.extract(extract_offset, extract_len)); + } + + extracted.width_ = length; + return extracted; + } + return std::vector(bits_.begin() + offset, bits_.begin() + offset + length); }