commit 794cc227dc9110fa89e36c5e6e9827d40d3046f0
author cschuldt <cschuldt@google.com> Mon Nov 29 15:56:37 2021
committer WebRTC LUCI CQ <webrtc-scoped@luci-project-accounts.iam.gserviceaccount.com> Wed Dec 01 14:52:21 2021
tree 2a6582824bae3df3871c1eb41b59146c7661fd59
parent 59b8a46d3f6a072ae3eba8ab86fdd91c39821ec6

Optimize RenderBuffer.

Changing to an index for-loop (instead of using std::transform) allows the compiler (clang for x86 at least) to use 3 different registers in the loop rather than just 1, resulting in less pipeline stall (I'd assume). Interestingly, the compiler unrolls the loop(s) completely in both cases.

Bug: None
Change-Id: I586773bc525e91bb6eb6638d5399928482306b9f
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/239364
Reviewed-by: Ivo Creusen <ivoc@webrtc.org>
Commit-Queue: Christian Schuldt <cschuldt@google.com>
Cr-Commit-Position: refs/heads/main@{#35453}

modules/audio_processing/aec3/render_buffer.cc

diff --git a/modules/audio_processing/aec3/render_buffer.cc b/modules/audio_processing/aec3/render_buffer.cc
index 60ea69c..aa511e2 100644
--- a/modules/audio_processing/aec3/render_buffer.cc
+++ b/modules/audio_processing/aec3/render_buffer.cc
@@ -42,8 +42,9 @@
   int position = spectrum_buffer_->read;
   for (size_t j = 0; j < num_spectra; ++j) {
     for (const auto& channel_spectrum : spectrum_buffer_->buffer[position]) {
-      std::transform(X2->begin(), X2->end(), channel_spectrum.begin(),
-                     X2->begin(), std::plus<float>());
+      for (size_t k = 0; k < X2->size(); ++k) {
+        (*X2)[k] += channel_spectrum[k];
+      }
     }
     position = spectrum_buffer_->IncIndex(position);
   }
@@ -60,18 +61,18 @@
   size_t j = 0;
   for (; j < num_spectra_shorter; ++j) {
     for (const auto& channel_spectrum : spectrum_buffer_->buffer[position]) {
-      std::transform(X2_shorter->begin(), X2_shorter->end(),
-                     channel_spectrum.begin(), X2_shorter->begin(),
-                     std::plus<float>());
+      for (size_t k = 0; k < X2_shorter->size(); ++k) {
+        (*X2_shorter)[k] += channel_spectrum[k];
+      }
     }
     position = spectrum_buffer_->IncIndex(position);
   }
   std::copy(X2_shorter->begin(), X2_shorter->end(), X2_longer->begin());
   for (; j < num_spectra_longer; ++j) {
     for (const auto& channel_spectrum : spectrum_buffer_->buffer[position]) {
-      std::transform(X2_longer->begin(), X2_longer->end(),
-                     channel_spectrum.begin(), X2_longer->begin(),
-                     std::plus<float>());
+      for (size_t k = 0; k < X2_longer->size(); ++k) {
+        (*X2_longer)[k] += channel_spectrum[k];
+      }
     }
     position = spectrum_buffer_->IncIndex(position);
   }