[LLD] Add --lto-CGO[0-3] option

Allow controlling the CodeGenOpt::Level independent of the LTO
optimization level in LLD via new options for the COFF, ELF, MachO, and
wasm frontends to lld. Most are spelled as --lto-CGO[0-3], but COFF is
spelled as -opt:lldltocgo=[0-3].

See D57422 for discussion surrounding the issue of how to set the CG opt
level. The ultimate goal is to let each function control its CG opt
level, but until then the current default means it is impossible to
specify a CG opt level lower than 2 while using LTO. This option gives
the user a means to control it for as long as it is not handled on a
per-function basis.

Reviewed By: MaskRay, #lld-macho, int3

Differential Revision: https://reviews.llvm.org/D141970

4 files changed, 21 insertions, 4 deletions

diff --git a/lld/MachO/Config.h b/lld/MachO/Config.h
index 220fb99d2e22..af46303f1ae2 100644
--- a/lld/MachO/Config.h
+++ b/lld/MachO/Config.h
@@ -26,6 +26,10 @@
 
 #include <vector>
 
+namespace llvm::CodeGenOpt {
+enum Level : int;
+} // namespace llvm::CodeGenOpt
+
 namespace lld {
 namespace macho {
 
@@ -165,6 +169,7 @@ struct Configuration {
   llvm::StringRef thinLTOJobs;
   llvm::StringRef umbrella;
   uint32_t ltoo = 2;
+  llvm::CodeGenOpt::Level ltoCgo;
   llvm::CachePruningPolicy thinLTOCachePolicy;
   llvm::StringRef thinLTOCacheDir;
   llvm::StringRef thinLTOIndexOnlyArg;
diff --git a/lld/MachO/Driver.cpp b/lld/MachO/Driver.cpp
index 65fea8958946..121fa851041c 100644
--- a/lld/MachO/Driver.cpp
+++ b/lld/MachO/Driver.cpp
@@ -1421,6 +1421,17 @@ bool macho::link(ArrayRef<const char *> argsArr, llvm::raw_ostream &stdoutOS,
   target = createTargetInfo(args);
   depTracker = std::make_unique<DependencyTracker>(
       args.getLastArgValue(OPT_dependency_info));
+
+  config->ltoo = args::getInteger(args, OPT_lto_O, 2);
+  if (config->ltoo > 3)
+    error("--lto-O: invalid optimization level: " + Twine(config->ltoo));
+  unsigned ltoCgo =
+      args::getInteger(args, OPT_lto_CGO, args::getCGOptLevel(config->ltoo));
+  if (auto level = CodeGenOpt::getLevel(ltoCgo))
+    config->ltoCgo = *level;
+  else
+    error("--lto-CGO: invalid codegen optimization level: " + Twine(ltoCgo));
+
   if (errorCount())
     return false;
 
@@ -1558,9 +1569,6 @@ bool macho::link(ArrayRef<const char *> argsArr, llvm::raw_ostream &stdoutOS,
     config->umbrella = arg->getValue();
   }
   config->ltoObjPath = args.getLastArgValue(OPT_object_path_lto);
-  config->ltoo = args::getInteger(args, OPT_lto_O, 2);
-  if (config->ltoo > 3)
-    error("--lto-O: invalid optimization level: " + Twine(config->ltoo));
   config->thinLTOCacheDir = args.getLastArgValue(OPT_cache_path_lto);
   config->thinLTOCachePolicy = getLTOCachePolicy(args);
   config->thinLTOEmitImportsFiles = args.hasArg(OPT_thinlto_emit_imports_files);
diff --git a/lld/MachO/LTO.cpp b/lld/MachO/LTO.cpp
index 2f5e9d06f396..6e3d4f3c230f 100644
--- a/lld/MachO/LTO.cpp
+++ b/lld/MachO/LTO.cpp
@@ -70,7 +70,7 @@ static lto::Config createConfig() {
   c.TimeTraceEnabled = config->timeTraceEnabled;
   c.TimeTraceGranularity = config->timeTraceGranularity;
   c.OptLevel = config->ltoo;
-  c.CGOptLevel = args::getCGOptLevel(config->ltoo);
+  c.CGOptLevel = config->ltoCgo;
   if (config->saveTemps)
     checkError(c.addSaveTemps(config->outputFile.str() + ".",
                               /*UseInputModulePath=*/true));
diff --git a/lld/MachO/Options.td b/lld/MachO/Options.td
index cb66f6277b5b..80a12f256b4b 100644
--- a/lld/MachO/Options.td
+++ b/lld/MachO/Options.td
@@ -84,6 +84,10 @@ def lto_O: Joined<["--"], "lto-O">,
     HelpText<"Set optimization level for LTO (default: 2)">,
     MetaVarName<"<opt-level>">,
     Group<grp_lld>;
+def lto_CGO: Joined<["--"], "lto-CGO">,
+    HelpText<"Set codegen optimization level for LTO (default: 2)">,
+    MetaVarName<"<cgopt-level>">,
+    Group<grp_lld>;
 def thinlto_cache_policy_eq: Joined<["--"], "thinlto-cache-policy=">,
     HelpText<"Pruning policy for the ThinLTO cache">,
     Group<grp_lld>;