[PATCH] D128298: [lld/mac] Parallelize code signature computation

[Nico Weber via Phabricator via llvm-commits]

thakis created this revision.
thakis added a reviewer: lld-macho.
Herald added projects: lld-macho, All.
thakis requested review of this revision.

According to ministat, this is a small but measurable speedup
(using the repro in PR56121):

  N           Min           Max        Median           Avg        Stddev

x  10     3.7439518     3.7783802     3.7730219     3.7655502   0.012375226
+  10     3.6149218      3.692198     3.6519327     3.6502951   0.025905601
Difference at 95.0% confidence

  -0.115255 +/- 0.0190746
  -3.06078% +/- 0.506554%
  (Student's t, pooled s = 0.0203008)

(Without 858e8b17f7365 <https://reviews.llvm.org/rG858e8b17f73652f9b79a8fd409b1f873c50ecd53>, this change here to use parallelFor is an 18% speedup,
and doing 858e8b17f7365 <https://reviews.llvm.org/rG858e8b17f73652f9b79a8fd409b1f873c50ecd53> on top of this change is just a 2.55 +/- 0.58% win.
Doing both results in a total speedup of 20.85 +/- 0.44%.)


https://reviews.llvm.org/D128298

Files:
  lld/MachO/SyntheticSections.cpp


Index: lld/MachO/SyntheticSections.cpp
===================================================================
--- lld/MachO/SyntheticSections.cpp
+++ lld/MachO/SyntheticSections.cpp
@@ -22,6 +22,7 @@
 #include "llvm/Support/EndianStream.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/LEB128.h"
+#include "llvm/Support/Parallel.h"
 #include "llvm/Support/Path.h"
 
 #if defined(__APPLE__)
@@ -1254,11 +1255,11 @@
   // NOTE: Changes to this functionality should be repeated in llvm-objcopy's
   // MachOWriter::writeSignatureData.
   uint8_t *hashes = buf + fileOff + allHeadersSize;
-  for (uint64_t i = 0; i < getBlockCount(); ++i) {
+  parallelFor(0, getBlockCount(), [&](size_t i) {
     sha256(buf + i * blockSize,
            std::min(static_cast<size_t>(fileOff - i * blockSize), blockSize),
            hashes + i * hashSize);
-  }
+  });
 #if defined(__APPLE__)
   // This is macOS-specific work-around and makes no sense for any
   // other host OS. See https://openradar.appspot.com/FB8914231


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