Sprinkle functools.lru_cache() in a few more places

This improves the backend generation time for gst-build from 7.4s to
6.6s. This is probably all the low-hanging fruit we can get, further
improvements will probably require refactoring, moving to pathlib.Path
or reimplementing CompilerArgs:

   222045    0.551    0.000    1.324    0.000 compilers.py:666(__iadd__)
     3691    0.230    0.000    0.885    0.000 ninjabackend.py:99(write)
   233560    0.441    0.000    0.701    0.000 posixpath.py:75(join)
      882    0.141    0.000    0.636    0.001 backends.py:509(generate_basic_compiler_args)
   256301    0.248    0.000    0.576    0.000 compilers.py:562(_can_dedup)
    37369    0.035    0.000    0.466    0.000 compilers.py:652(extend_direct)
    74650    0.067    0.000    0.431    0.000 compilers.py:641(append_direct)
   158153    0.089    0.000    0.405    0.000 ninjabackend.py:129(<lambda>)
      845    0.064    0.000    0.391    0.000 ninjabackend.py:279(get_target_generated_sources)
    58161    0.070    0.000    0.317    0.000 backends.py:217(get_target_generated_dir)
   216825    0.175    0.000    0.275    0.000 ninjabackend.py:48(ninja_quote)
      845    0.058    0.000    0.255    0.000 ninjabackend.py:2289(guess_external_link_dependencies)
      845    0.068    0.000    0.239    0.000 backends.py:793(get_custom_target_provided_libraries)
    52101    0.030    0.000    0.237    0.000 compilers.py:716(append)
  1319326    0.231    0.000    0.231    0.000 {built-in method builtins.isinstance}
  1189117    0.229    0.000    0.229    0.000 {method 'startswith' of 'str' objects}
     3235    0.102    0.000    0.228    0.000 compilers.py:614(to_native)

Note: there are 845 build targets.

2 files changed, 13 insertions, 16 deletions

diff --git a/mesonbuild/compilers/c.py b/mesonbuild/compilers/c.py
index bde9f63..1d531a6 100644
--- a/mesonbuild/compilers/c.py
+++ b/mesonbuild/compilers/c.py
@@ -119,6 +119,7 @@ class CCompiler(Compiler):
         return None, fname
 
     # The default behavior is this, override in MSVC
+    @functools.lru_cache(maxsize=None)
     def build_rpath_args(self, build_dir, from_dir, rpath_paths, build_rpath, install_rpath):
         if self.id == 'clang' and self.clang_type == compilers.CLANG_OSX:
             return self.build_osx_rpath_args(build_dir, rpath_paths, build_rpath)
@@ -222,7 +223,7 @@ class CCompiler(Compiler):
             p = Path(p)
             if p.exists():
                 paths.append(p.resolve().as_posix())
-        return paths
+        return tuple(paths)
 
     def get_compiler_dirs(self, env, name):
         '''
@@ -232,23 +233,19 @@ class CCompiler(Compiler):
         for line in stdo.split('\n'):
             if line.startswith(name + ':'):
                 return CCompiler._split_fetch_real_dirs(line.split('=', 1)[1])
-        return []
+        return ()
 
+    @functools.lru_cache()
     def get_library_dirs(self, env):
-        key = (tuple(self.exelist), env)
-        if key not in self.library_dirs_cache:
-            self.library_dirs_cache[key] = self.get_compiler_dirs(env, 'libraries')
-        return self.library_dirs_cache[key][:]
+        return self.get_compiler_dirs(env, 'libraries')
 
+    @functools.lru_cache()
     def get_program_dirs(self, env):
         '''
         Programs used by the compiler. Also where toolchain DLLs such as
         libstdc++-6.dll are found with MinGW.
         '''
-        key = (tuple(self.exelist), env)
-        if key not in self.program_dirs_cache:
-            self.program_dirs_cache[key] = self.get_compiler_dirs(env, 'programs')
-        return self.program_dirs_cache[key][:]
+        return self.get_compiler_dirs(env, 'programs')
 
     def get_pic_args(self):
         return ['-fPIC']
@@ -907,7 +904,7 @@ class CCompiler(Compiler):
             patterns += self._get_patterns(env, prefixes, stlibext, False)
         else:
             raise AssertionError('BUG: unknown libtype {!r}'.format(libtype))
-        return patterns
+        return tuple(patterns)
 
     @staticmethod
     def _sort_shlibs_openbsd(libs):
diff --git a/mesonbuild/compilers/compilers.py b/mesonbuild/compilers/compilers.py
index 88e9bce..40d6880 100644
--- a/mesonbuild/compilers/compilers.py
+++ b/mesonbuild/compilers/compilers.py
@@ -923,7 +923,7 @@ class Compiler:
         raise EnvironmentException('Language {} does not support library finding.'.format(self.get_display_language()))
 
     def get_library_dirs(self, *args, **kwargs):
-        return []
+        return ()
 
     def has_multi_arguments(self, args, env):
         raise EnvironmentException(
@@ -1381,12 +1381,12 @@ class ElbrusCompiler(GnuCompiler):
         os_env = os.environ.copy()
         os_env['LC_ALL'] = 'C'
         stdo = Popen_safe(self.exelist + ['--print-search-dirs'], env=os_env)[1]
-        paths = []
+        paths = ()
         for line in stdo.split('\n'):
             if line.startswith('libraries:'):
                 # lcc does not include '=' in --print-search-dirs output.
                 libstr = line.split(' ', 1)[1]
-                paths = [os.path.realpath(p) for p in libstr.split(':')]
+                paths = (os.path.realpath(p) for p in libstr.split(':'))
                 break
         return paths
 
@@ -1394,12 +1394,12 @@ class ElbrusCompiler(GnuCompiler):
         os_env = os.environ.copy()
         os_env['LC_ALL'] = 'C'
         stdo = Popen_safe(self.exelist + ['--print-search-dirs'], env=os_env)[1]
-        paths = []
+        paths = ()
         for line in stdo.split('\n'):
             if line.startswith('programs:'):
                 # lcc does not include '=' in --print-search-dirs output.
                 libstr = line.split(' ', 1)[1]
-                paths = [os.path.realpath(p) for p in libstr.split(':')]
+                paths = (os.path.realpath(p) for p in libstr.split(':'))
                 break
         return paths