Bobby R. Bruce has uploaded this change for review. (
https://gem5-review.googlesource.com/c/public/gem5/+/44887 )
Change subject: scons: Add `--with-lto` flag to enabled LTO for all builds
......................................................................
scons: Add `--with-lto` flag to enabled LTO for all builds
Change-Id: I2eea7d447703491675c02730707cf9026cface5f
---
M SConstruct
M src/SConscript
2 files changed, 50 insertions(+), 25 deletions(-)
diff --git a/SConstruct b/SConstruct
index f3d65f0..d192b91 100755
--- a/SConstruct
+++ b/SConstruct
@@ -107,6 +107,8 @@
help="Don't compress debug info in build files")
AddOption('--no-lto', action='store_true',
help='Disable Link-Time Optimization for fast')
+AddOption('--with-lto', action='store_true',
+ help='Enable Link-Time Optimization')
AddOption('--verbose', action='store_true',
help='Print full tool command lines')
AddOption('--without-python', action='store_true',
@@ -262,9 +264,32 @@
main.Prepend(CPPPATH=Dir('include'))
# Initialize the Link-Time Optimization (LTO) flags
+
+if GetOption('no_lto') and GetOption('with_lto'):
+ error('\n'.join((
+ "`--no-lto` and `--with-lto` are both set. These are mutually ",
+ "exclusive flags. `--no-lto` disables LTO for .fast builds ",
+ "(enabled by default). `--with-lto` enables LTO for all
builds.")))
+
+
main['LTO_CCFLAGS'] = []
main['LTO_LDFLAGS'] = []
+# THE LTO flags to set for the .fast builds only (the other builds use
+# 'LTO_CCFLAGS' and 'LTO_LDFLAGS')
+main['LTO_CCFLAGS_FAST'] = []
+main['LTO_LDFLAGS_FAST'] = []
+
+lto_flags_to_set = []
+
+if not GetOption('no_lto'):
+ lto_flags_to_set.append('LTO_CCFLAGS_FAST')
+ lto_flags_to_set.append('LTO_LDFLAGS_FAST')
+ if GetOption('with_lto'):
+ lto_flags_to_set.append('LTO_CCFLAGS')
+ lto_flags_to_set.append('LTO_LDFLAGS')
+
+
# According to the readme, tcmalloc works best if the compiler doesn't
# assume that we're using the builtin malloc and friends. These flags
# are compiler-specific, so we need to set them after we detect which
@@ -329,22 +354,23 @@
'Installed version:', main['CXXVERSION'])
# Add the appropriate Link-Time Optimization (LTO) flags
- # unless LTO is explicitly turned off. Note that these flags
- # are only used by the fast target.
- if not GetOption('no_lto'):
- # g++ uses "make" to parallelize LTO. The program can be overriden
with
- # the environment variable "MAKE", but we currently make no
attempt to
- # plumb that variable through.
- parallelism = ''
- if main.Detect('make'):
- parallelism = '=%d' % GetOption('num_jobs')
- else:
- warning('"make" not found, link time optimization will be '
- 'single threaded.')
+ # Note that these flags are only used by .fast by default. If
`--no-lto` is
+ # set .fast will link without LTO. If `--with-lto` is set, all gem5
+ # variants (opt, debug, etc.) are linked with LTO.
+ #
+ # g++ uses "make" to parallelize LTO. The program can be overriden with
+ # the environment variable "MAKE", but we currently make no attempt to
+ # plumb that variable through.
+ parallelism = ''
+ if main.Detect('make'):
+ parallelism = '=%d' % GetOption('num_jobs')
+ else:
+ warning('"make" not found, link time optimization will be '
+ 'single threaded.')
- for var in 'LTO_CCFLAGS', 'LTO_LDFLAGS':
- # Use the same amount of jobs for LTO as we are running scons
with.
- main[var] = ['-flto%s' % parallelism]
+ for var in lto_flags_to_set:
+ # Use the same amount of jobs for LTO as we are running scons with.
+ main[var] = ['-flto%s' % parallelism]
main.Append(TCMALLOC_CCFLAGS=['-fno-builtin-malloc', '-fno-builtin-calloc',
'-fno-builtin-realloc', '-fno-builtin-free'])
@@ -354,10 +380,8 @@
error('clang version 3.9 or newer required.\n'
'Installed version:', main['CXXVERSION'])
- # If not disabled, set the Link-Time Optimization (LTO) flags.
- if not GetOption('no_lto'):
- for var in 'LTO_CCFLAGS', 'LTO_LDFLAGS':
- main[var] = ['-flto']
+ for var in lto_flags_to_set:
+ main[var] = ['-flto']
# clang has a few additional warnings that we disable.
with gem5_scons.Configure(main) as conf:
diff --git a/src/SConscript b/src/SConscript
index 47aa2ea..1daf3e6 100644
--- a/src/SConscript
+++ b/src/SConscript
@@ -1431,15 +1431,16 @@
else:
ccflags['debug'] += ['-ggdb3']
ldflags['debug'] += ['-O0']
- # opt, fast, prof and perf all share the same cc flags, also add
+ # opt, prof and perf all share the same cc flags, also add
# the optimization to the ldflags as LTO defers the optimization
# to link time
- for target in ['opt', 'fast', 'prof', 'perf']:
- ccflags[target] += ['-O3']
- ldflags[target] += ['-O3']
+ for target in ['opt', 'prof', 'perf']:
+ ccflags[target] += ['-O3'] + env['LTO_CCFLAGS']
+ ldflags[target] += ['-O3'] + env['LTO_LDFLAGS']
- ccflags['fast'] += env['LTO_CCFLAGS']
- ldflags['fast'] += env['LTO_LDFLAGS']
+ ccflags['fast'] += ['-O3'] + env['LTO_CCFLAGS_FAST']
+ ldflags['fast'] += ['-O3'] + env['LTO_LDFLAGS_FAST']
+
elif env['CLANG']:
ccflags['debug'] += ['-g', '-O0']
# opt, fast, prof and perf all share the same cc flags
--
To view, visit https://gem5-review.googlesource.com/c/public/gem5/+/44887
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Gerrit-Project: public/gem5
Gerrit-Branch: develop
Gerrit-Change-Id: I2eea7d447703491675c02730707cf9026cface5f
Gerrit-Change-Number: 44887
Gerrit-PatchSet: 1
Gerrit-Owner: Bobby R. Bruce <[email protected]>
Gerrit-MessageType: newchange
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