compilers: Add b_lto and b_pgo support for MSVC

docs/markdown/snippets/msvc_lto.md

@@ -0,0 +1,5 @@
+## `-Db_lto` and `-Db_pgo` now supported for MSVC
+
+`-Db_lto` is now supported for MSVC's `/LTCG`, as is `-Db_lto_mode=thin`
+for `/LTCG:INCREMENTAL`. `-Db_pgo` is also supported, and should be used
+alongside `-Db_lto=true`.

mesonbuild/compilers/mixins/visualstudio.py

@@ -17,7 +17,7 @@
 from ... import mlog
 from mesonbuild.compilers.compilers import CompileCheckMode
 from ...options import OptionKey
-from mesonbuild.linkers.linkers import ClangClDynamicLinker
+from mesonbuild.linkers.linkers import ClangClDynamicLinker, MSVCDynamicLinker
 
 if T.TYPE_CHECKING:
     from ...build import BuildTarget
@@ -388,6 +388,8 @@ class MSVCCompiler(VisualStudioLikeCompiler):
     def __init__(self, target: str):
         super().__init__(target)
 
+        self.base_options.update({OptionKey('b_lto'), OptionKey('b_lto_mode'), OptionKey('b_pgo')})
+
         # Visual Studio 2013 and earlier don't support the /utf-8 argument.
         # We want to remove it. We also want to make an explicit copy so we
         # don't mutate class constant state
@@ -427,6 +429,35 @@ def get_pch_base_name(self, header: str) -> str:
     def should_link_pch_object(self) -> bool:
         return True
 
+    def get_lto_compile_args(self, *, target: T.Optional[BuildTarget] = None, threads: int = 0,
+                             mode: str = 'default') -> T.List[str]:
+        args: T.List[str] = ['/GL']
+        if mode == 'thin':
+            args.append('/Gy')
+        return args
+
+    def get_lto_link_args(self, *, target: T.Optional[BuildTarget] = None, threads: int = 0,
+                          mode: str = 'default', thinlto_cache_dir: T.Optional[str] = None) -> T.List[str]:
+        args: T.List[str] = []
+        # LTO data generated by MSVC is only usable by link
+        if not isinstance(self.linker, MSVCDynamicLinker):
+            raise mesonlib.MesonException(f"MSVC's LTCG only works with link, not {self.linker.id}")
+        if mode == 'default':
+            args.append('/LTCG')
+        elif mode == 'thin':
+            args.append('/LTCG:INCREMENTAL')
+        return args
+
+    def get_profile_generate_args(self) -> T.List[str]:
+        if not isinstance(self.linker, MSVCDynamicLinker):
+            raise mesonlib.MesonException(f"MSVC's PGO only works with link, not {self.linker.id}")
+        return self.linker_to_compiler_args(['/GENPROFILE'])
+
+    def get_profile_use_args(self) -> T.List[str]:
+        if not isinstance(self.linker, MSVCDynamicLinker):
+            raise mesonlib.MesonException(f"MSVC's PGO only works with link, not {self.linker.id}")
+        return self.linker_to_compiler_args(['/USEPROFILE'])
+
 class ClangClCompiler(VisualStudioLikeCompiler):
 
     """Specific to Clang-CL."""

mesonbuild/linkers/linkers.py

@@ -1509,6 +1509,9 @@ def get_win_subsystem_args(self, value: str) -> T.List[str]:
     def fatal_warnings(self) -> T.List[str]:
         return ['-WX']
 
+    def get_lto_args(self) -> T.List[str]:
+        return ['/LTCG']
+
 
 class ClangClDynamicLinker(VisualStudioLikeLinkerMixin, DynamicLinker):