[lld] 44978a2 - [lld/mac] Write output sections in parallel

[Nico Weber via llvm-commits]

Author: Michael Eisel
Date: 2022-06-08T20:11:50-04:00
New Revision: 44978a234b8e2ad5f112d6b5910ee129bd52d54b

URL: https://github.com/llvm/llvm-project/commit/44978a234b8e2ad5f112d6b5910ee129bd52d54b
DIFF: https://github.com/llvm/llvm-project/commit/44978a234b8e2ad5f112d6b5910ee129bd52d54b.diff

LOG: [lld/mac] Write output sections in parallel

This reduces linking time by ~8% for my project (1.19s -> 0.53s for
writeSections()). writeTo is const, which bodes well for it being
parallelizable, and I've looked through the different overridden versions and
can't see any race conditions. It produces the same byte-for-byte output for my
project.

Differential Revision: https://reviews.llvm.org/D126800

Added: 
    

Modified: 
    lld/MachO/Writer.cpp
    lld/test/MachO/invalid/range-check.s

Removed: 
    


################################################################################
diff  --git a/lld/MachO/Writer.cpp b/lld/MachO/Writer.cpp
index 3fbf520657d12..a485ba97d8d39 100644
--- a/lld/MachO/Writer.cpp
+++ b/lld/MachO/Writer.cpp
@@ -20,6 +20,7 @@
 #include "SyntheticSections.h"
 #include "Target.h"
 #include "UnwindInfoSection.h"
+#include "llvm/Support/Parallel.h"
 
 #include "lld/Common/Arrays.h"
 #include "lld/Common/CommonLinkerContext.h"
@@ -1081,9 +1082,13 @@ void Writer::openFile() {
 
 void Writer::writeSections() {
   uint8_t *buf = buffer->getBufferStart();
+  std::vector<const OutputSection *> osecs;
   for (const OutputSegment *seg : outputSegments)
-    for (const OutputSection *osec : seg->getSections())
-      osec->writeTo(buf + osec->fileOff);
+    append_range(osecs, seg->getSections());
+
+  parallelForEach(osecs.begin(), osecs.end(), [&](const OutputSection *osec) {
+    osec->writeTo(buf + osec->fileOff);
+  });
 }
 
 // In order to utilize multiple cores, we first split the buffer into chunks,

diff  --git a/lld/test/MachO/invalid/range-check.s b/lld/test/MachO/invalid/range-check.s
index 2f087e38c2662..1ad719cfa31d2 100644
--- a/lld/test/MachO/invalid/range-check.s
+++ b/lld/test/MachO/invalid/range-check.s
@@ -6,11 +6,11 @@
 # RUN: %lld -dylib %t/bar.o -o %t/libbar.dylib
 # RUN: not %lld -lSystem -o /dev/null %t/libbar.dylib %t/test.o 2>&1 | FileCheck %s
 
-# CHECK: error: {{.*}}test.o:(symbol _main+0xd): relocation UNSIGNED is out of range: [[#]] is not in [0, 4294967295]; references _foo
-# CHECK: error: {{.*}}test.o:(symbol _main+0x3): relocation GOT_LOAD is out of range: [[#]] is not in [-2147483648, 2147483647]; references _foo
-# CHECK: error: stub is out of range: [[#]] is not in [-2147483648, 2147483647]; references _bar
-# CHECK: error: stub helper header is out of range: [[#]] is not in [-2147483648, 2147483647]
-# CHECK: error: stub helper header is out of range: [[#]] is not in [-2147483648, 2147483647]
+# CHECK-DAG: error: {{.*}}test.o:(symbol _main+0xd): relocation UNSIGNED is out of range: [[#]] is not in [0, 4294967295]; references _foo
+# CHECK-DAG: error: {{.*}}test.o:(symbol _main+0x3): relocation GOT_LOAD is out of range: [[#]] is not in [-2147483648, 2147483647]; references _foo
+# CHECK-DAG: error: stub is out of range: [[#]] is not in [-2147483648, 2147483647]; references _bar
+# CHECK-DAG: error: stub helper header is out of range: [[#]] is not in [-2147483648, 2147483647]
+# CHECK-DAG: error: stub helper header is out of range: [[#]] is not in [-2147483648, 2147483647]
 
 #--- bar.s
 .globl _bar