[build-script] Allow to tune dsymutil parallelism (#34795)

This should enable scaling when using machines with large amount of
RAM.

To better support machines with lower spec, process one binary per
dsymutil invocation (reverting #34149).

Add some (limited) facilities to gather the time taken to execute
dsymutil to better assist in tuning the parameter -- these are printed in
JSON format in the log to allow for easier scraping

```
{ "command": "dsymutil", "start": "2020-11-18T18:10:47" }
{ "command": "dsymutil", "end": "2020-11-18T18:14:45" }
```

Addresses rdar://71018443

Author: edymtt

utils/build-script

@@ -501,6 +501,7 @@ class BuildScriptInvocation(object):
                 pipes.quote(opt) for opt in cmake.common_options()),
             "--build-args=%s" % ' '.join(
                 pipes.quote(arg) for arg in cmake.build_args()),
+            "--dsymutil-jobs", str(args.dsymutil_jobs),
         ]
 
         # Compute any product specific cmake arguments.

utils/build-script-impl

@@ -71,6 +71,7 @@ KNOWN_SETTINGS=(
     swift-tools-num-parallel-lto-link-jobs        ""                "The number of parallel link jobs to use when compiling swift tools"
     use-gold-linker                               ""                "Enable using the gold linker"
     workspace                                     "${HOME}/src"     "source directory containing llvm, clang, swift"
+    dsymutil-jobs                                 "1"               "number of parallel invocations of dsymutil"
 
     ## Build Tools
     host-cc                                       ""                "the path to CC, the 'clang' compiler for the host platform. **This argument is required**"
@@ -3015,6 +3016,25 @@ for host in "${ALL_HOSTS[@]}"; do
     done
 done
 
+function printJSONTimestamp() {
+    local command=$1
+    local kind=$2
+
+    echo "{ \"command\": \"${command}\", \"${kind}\": \"$(date "+%Y-%m-%dT%H:%M:%S")\" }"
+}
+
+function printJSONStartTimestamp() {
+    local command=$1
+
+    printJSONTimestamp ${command} "start"
+}
+
+function printJSONEndTimestamp() {
+    local command=$1
+
+    printJSONTimestamp ${command} "end"
+}
+
 for host in "${ALL_HOSTS[@]}"; do
     # Check if we should perform this action.
     if ! [[ $(should_execute_action "${host}-extractsymbols") ]]; then
@@ -3047,6 +3067,9 @@ for host in "${ALL_HOSTS[@]}"; do
         #        Instead, just echo we do "darwin_intall_extract_symbols".
         if [[ "${DRY_RUN}" ]]; then
             call darwin_install_extract_symbols
+            printJSONStartTimestamp dsymutil
+            echo xargs -n 1 -P ${DSYMUTIL_JOBS} dsymutil
+            printJSONEndTimestamp dsymutil
         else
             set -x
 
@@ -3069,13 +3092,16 @@ for host in "${ALL_HOSTS[@]}"; do
             #
             # Exclude shell scripts and static archives.
             # Exclude swift-api-digester dSYM to reduce debug toolchain size.
-            # Run sequentially -- dsymutil is multithreaded and can be memory intensive
+            # Tweak carefully the amount of parallelism -- dsymutil can be memory intensive and
+            # as such too many instance can exhaust the memory and slow down/panic the machine
+            printJSONStartTimestamp dsymutil
             (cd "${host_symroot}" &&
              find ./"${CURRENT_PREFIX}" -perm -0111 -type f -print | \
                grep -v '.py$' | \
                grep -v '.a$' | \
                grep -v 'swift-api-digester' | \
-               xargs -P 1 ${dsymutil_path})
+               xargs -n 1 -P ${DSYMUTIL_JOBS} ${dsymutil_path})
+            printJSONEndTimestamp dsymutil
 
             # Strip executables, shared libraries and static libraries in
             # `host_install_destdir`.

utils/build_swift/build_swift/defaults.py

@@ -22,7 +22,7 @@
 
 
 __all__ = [
-    # Command line configuarable
+    # Command line configurable
     'BUILD_VARIANT',
     'CMAKE_GENERATOR',
     'COMPILER_VENDOR',
@@ -38,6 +38,7 @@
     'DARWIN_INSTALL_PREFIX',
     'LLVM_MAX_PARALLEL_LTO_LINK_JOBS',
     'SWIFT_MAX_PARALLEL_LTO_LINK_JOBS',
+    'DSYMUTIL_JOBS'
 
     # Constants
 ]
@@ -62,6 +63,8 @@
 DARWIN_INSTALL_PREFIX = ('/Applications/Xcode.app/Contents/Developer/'
                          'Toolchains/XcodeDefault.xctoolchain/usr')
 
+DSYMUTIL_JOBS = 1
+
 
 def _system_memory():
     """Returns the system memory as an int. None if the system memory cannot

utils/build_swift/build_swift/driver_arguments.py

@@ -486,6 +486,13 @@ def create_argument_parser():
            help='the maximum number of parallel link jobs to use when '
                 'compiling swift tools.')
 
+    option('--dsymutil-jobs', store_int,
+           default=defaults.DSYMUTIL_JOBS,
+           metavar='COUNT',
+           help='the maximum number of parallel dsymutil jobs to use when '
+                'extracting symbols. Tweak with caution, since dsymutil'
+                'is memory intensive.')
+
     option('--disable-guaranteed-normal-arguments', store_true,
            help='Disable guaranteed normal arguments')
 

utils/build_swift/tests/expected_options.py

@@ -140,6 +140,7 @@
     'distcc': False,
     'sccache': False,
     'dry_run': False,
+    'dsymutil_jobs': defaults.DSYMUTIL_JOBS,
     'enable_asan': False,
     'enable_experimental_differentiable_programming': True,
     'enable_experimental_concurrency': True,
@@ -662,6 +663,7 @@ class BuildScriptImplOption(_BaseOption):
     IntOption('--llvm-max-parallel-lto-link-jobs'),
     IntOption('--swift-tools-max-parallel-lto-link-jobs'),
     IntOption('-j', dest='build_jobs'),
+    IntOption('--dsymutil-jobs', dest='dsymutil_jobs'),
 
     AppendOption('--cross-compile-hosts'),
     AppendOption('--extra-cmake-options'),

validation-test/BuildSystem/dsymutil_jobs.test

@@ -0,0 +1,10 @@
+# RUN: %empty-directory(%t)
+# RUN: mkdir -p %t
+# RUN: SKIP_XCODE_VERSION_CHECK=1 SWIFT_BUILD_ROOT=%t %swift_src_root/utils/build-script --dry-run --darwin-install-extract-symbols --dsymutil-jobs 5 --cmake %cmake 2>&1 | %FileCheck %s
+
+# REQUIRES: standalone_build,OS=macosx
+
+# CHECK: --- Extracting symbols ---
+# CHECK: { "command": "dsymutil", "start": "
+# CHECK-NEXT: xargs -n 1 -P 5 dsymutil
+# CHECK-NEXT: { "command": "dsymutil", "end": "