From ae9b23832e3ef4064e5735265ce7008794ab0491 Mon Sep 17 00:00:00 2001
From: Nirbheek Chauhan <nirbheek@centricular.com>
Date: Fri, 2 Jun 2017 05:25:17 +0530
Subject: ninja: De-dup libraries and use --start/end-group

Now we aggressively de-dup the list of libraries used while linking,
and when linking with GNU ld we have to enclose all static libraries
with -Wl,--start-group and -Wl,--end-group to force the linker to
resolve all symbols recursively. This is needed when static libraries
have circular deps on each other (see included test).

The --start/end-group change is also needed for circular dependencies
between static libraries because we no longer recursively list out all
library dependencies.

The size of build.ninja for GStreamer is now down to 6.1M from 20M,
and yields a net reduction in configuration time of 10%
---
 mesonbuild/compilers.py | 50 ++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 45 insertions(+), 5 deletions(-)

(limited to 'mesonbuild/compilers.py')

diff --git a/mesonbuild/compilers.py b/mesonbuild/compilers.py
index e7c02b2..d0f3349 100644
--- a/mesonbuild/compilers.py
+++ b/mesonbuild/compilers.py
@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import re
 import shutil
 import contextlib
 import subprocess, os.path
@@ -375,10 +376,15 @@ class CompilerArgs(list):
     # Arg prefixes that override by prepending instead of appending
     prepend_prefixes = ('-I', '-L')
     # Arg prefixes and args that must be de-duped by returning 2
-    dedup2_prefixes = ('-I', '-L', '-D')
+    dedup2_prefixes = ('-I', '-L', '-D', '-U')
+    dedup2_suffixes = ()
     dedup2_args = ()
     # Arg prefixes and args that must be de-duped by returning 1
-    dedup1_prefixes = ()
+    dedup1_prefixes = ('-l',)
+    dedup1_suffixes = ('.lib', '.dll', '.so', '.dylib', '.a')
+    # Match a .so of the form path/to/libfoo.so.0.1.0
+    # Only UNIX shared libraries require this. Others have a fixed extension.
+    dedup1_regex = re.compile(r'([\/\\]|\A)lib.*\.so(\.[0-9]+)?(\.[0-9]+)?(\.[0-9]+)?$')
     dedup1_args = ('-c', '-S', '-E', '-pipe', '-pthread')
     compiler = None
 
@@ -416,7 +422,7 @@ class CompilerArgs(list):
     def _can_dedup(cls, arg):
         '''
         Returns whether the argument can be safely de-duped. This is dependent
-        on two things:
+        on three things:
 
         a) Whether an argument can be 'overriden' by a later argument.  For
            example, -DFOO defines FOO and -UFOO undefines FOO. In this case, we
@@ -430,10 +436,20 @@ class CompilerArgs(list):
            a particular argument is present. This can matter for symbol
            resolution in static or shared libraries, so we cannot de-dup or
            reorder them. For these we return `0`. This is the default.
+
+        In addition to these, we handle library arguments specially.
+        With GNU ld, we surround library arguments with -Wl,--start/end-group
+        to recursively search for symbols in the libraries. This is not needed
+        with other linkers.
         '''
-        if arg.startswith(cls.dedup2_prefixes) or arg in cls.dedup2_args:
+        if arg in cls.dedup2_args or \
+           arg.startswith(cls.dedup2_prefixes) or \
+           arg.endswith(cls.dedup2_suffixes):
             return 2
-        if arg.startswith(cls.dedup1_prefixes) or arg in cls.dedup1_args:
+        if arg in cls.dedup1_args or \
+           arg.startswith(cls.dedup1_prefixes) or \
+           arg.endswith(cls.dedup1_suffixes) or \
+           re.search(cls.dedup1_regex, arg):
             return 1
         return 0
 
@@ -444,6 +460,21 @@ class CompilerArgs(list):
         return False
 
     def to_native(self):
+        # Check if we need to add --start/end-group for circular dependencies
+        # between static libraries.
+        if get_compiler_uses_gnuld(self.compiler):
+            group_started = False
+            for each in self:
+                if not each.startswith('-l') and not each.endswith('.a'):
+                    continue
+                i = self.index(each)
+                if not group_started:
+                    # First occurance of a library
+                    self.insert(i, '-Wl,--start-group')
+                    group_started = True
+            # Last occurance of a library
+            if group_started:
+                self.insert(i + 1, '-Wl,--end-group')
         return self.compiler.unix_args_to_native(self)
 
     def __add__(self, args):
@@ -2402,6 +2433,15 @@ def get_compiler_is_linuxlike(compiler):
         return True
     return False
 
+def get_compiler_uses_gnuld(c):
+    # FIXME: Perhaps we should detect the linker in the environment?
+    # FIXME: Assumes that *BSD use GNU ld, but they might start using lld soon
+    if (getattr(c, 'gcc_type', None) in (GCC_STANDARD, GCC_MINGW, GCC_CYGWIN)) or \
+       (getattr(c, 'clang_type', None) in (CLANG_STANDARD, CLANG_WIN)) or \
+       (getattr(c, 'icc_type', None) in (ICC_STANDARD, ICC_WIN)):
+        return True
+    return False
+
 def get_largefile_args(compiler):
     '''
     Enable transparent large-file-support for 32-bit UNIX systems
-- 
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