COFF: Introduce flag /opt:lldlto=N for controlling LTO optimization level.

[ruiu]

LGTM

COFF/Driver.cpp

376

Remove parentheses around the string literal.

COFF/Config.h

struct Configuration {
 
   // Used for SafeSEH.
   DefinedRelative *SEHTable = nullptr;
   DefinedAbsolute *SEHCount = nullptr;
 
   // Used for /opt:icf
   bool ICF = false;
 
+  // Used for /opt:lldlto=N
+  unsigned LTOOptLevel = 2;
+
   // Used for /merge:from=to (e.g. /merge:.rdata=.text)
   std::map<StringRef, StringRef> Merge;
 
   // Options for manifest files.
   ManifestKind Manifest = SideBySide;
   int ManifestID = 1;
   StringRef ManifestDependency;
   bool ManifestUAC = true;

COFF/Driver.cpp

for (auto *Arg : Args.filtered(OPT_opt)) {
     if (S == "noref") {
       Config->DoGC = false;
       continue;
     }
     if (S == "lldicf") {
       Config->ICF = true;
       continue;
     }
+    if (StringRef(S).startswith("lldlto=")) {
+      StringRef OptLevel = StringRef(S).substr(7);
+      if (OptLevel.getAsInteger(10, Config->LTOOptLevel) ||
+          Config->LTOOptLevel > 3) {
+        error(("/opt:lldlto: invalid optimization level: ") + OptLevel);
+      }
+      continue;
+    }
     if (S != "ref" && S != "icf" && S != "noicf" &&
         S != "lbr" && S != "nolbr" &&
         !StringRef(S).startswith("icf=")) {
       error(Twine("/opt: unknown option: ") + S);
     }
   }
 
   // Handle /failifmismatch

COFF/SymbolTable.cpp

void SymbolTable::addCombinedLTOObject() {
   // Diagnose any undefined symbols early, but do not resolve weak externals,
   // as resolution breaks the invariant that each Symbol points to a unique
   // SymbolBody, which we rely on to replace DefinedBitcode symbols correctly.
   reportRemainingUndefines(/*Resolve=*/false);
 
   // Create an object file and add it to the symbol table by replacing any
   // DefinedBitcode symbols with the definitions in the object file.
   LTOCodeGenerator CG;
+  CG.setOptLevel(Config->LTOOptLevel);
   ObjectFile *Obj = createLTOObject(&CG);
 
   for (SymbolBody *Body : Obj->getSymbols()) {
     if (!Body->isExternal())
       continue;
     // We should not see any new undefined symbols at this point, but we'll
     // diagnose them later in reportRemainingUndefines().
     StringRef Name = Body->getName();

test/COFF/lto-opt-level.ll

+; RUN: llvm-as -o %t.obj %s
+; RUN: lld-link /out:%t0.exe /entry:main /subsystem:console /opt:lldlto=0 /debug %t.obj
+; RUN: llvm-nm %t0.exe | FileCheck --check-prefix=CHECK-O0 %s
+; RUN: lld-link /out:%t2.exe /entry:main /subsystem:console /opt:lldlto=2 /debug %t.obj
+; RUN: llvm-nm %t2.exe | FileCheck --check-prefix=CHECK-O2 %s
+; RUN: lld-link /out:%t2a.exe /entry:main /subsystem:console /debug %t.obj
+; RUN: llvm-nm %t2a.exe | FileCheck --check-prefix=CHECK-O2 %s
+
+; CHECK-O0: foo
+; CHECK-O2-NOT: foo
+define internal void @foo() {
+  ret void
+}
+
+define void @main() {
+  call void @foo()
+  ret void
+}