[ELF] Support explicitly overriding relocation model in LTO

lld currently selects the relocation model automatically depending on
the link flags specified, but in some cases it'd be useful to allow
explicitly overriding the relocation model using a flag.

llvm-svn: 366644

Author: petrhosek

lld/Common/TargetOptionsCommandFlags.cpp

@@ -26,6 +26,10 @@ llvm::TargetOptions lld::initTargetOptionsFromCodeGenFlags() {
   return ::InitTargetOptionsFromCodeGenFlags();
 }
 
+llvm::Optional<llvm::Reloc::Model> lld::getRelocModelFromCMModel() {
+  return getRelocModel();
+}
+
 llvm::Optional<llvm::CodeModel::Model> lld::getCodeModelFromCMModel() {
   return getCodeModel();
 }

lld/ELF/LTO.cpp

@@ -76,7 +76,9 @@ static lto::Config createConfig() {
   c.Options.FunctionSections = true;
   c.Options.DataSections = true;
 
-  if (config->relocatable)
+  if (auto relocModel = getRelocModelFromCMModel())
+    c.RelocModel = *relocModel;
+  else if (config->relocatable)
     c.RelocModel = None;
   else if (config->isPic)
     c.RelocModel = Reloc::PIC_;

lld/include/lld/Common/TargetOptionsCommandFlags.h

@@ -16,6 +16,7 @@
 
 namespace lld {
 llvm::TargetOptions initTargetOptionsFromCodeGenFlags();
+llvm::Optional<llvm::Reloc::Model> getRelocModelFromCMModel();
 llvm::Optional<llvm::CodeModel::Model> getCodeModelFromCMModel();
 std::string getCPUStr();
 std::vector<std::string> getMAttrs();

lld/test/ELF/lto/relocation-model.ll

@@ -33,6 +33,15 @@
 ; RUN: llvm-readobj -r %t-out.lto.o | FileCheck %s --check-prefix=PIC
 
 
+;; Explicit flag.
+
+; RUN: ld.lld %t.o -o %t-out -save-temps -r -mllvm -relocation-model=pic
+; RUN: llvm-readobj -r %t-out.lto.o | FileCheck %s --check-prefix=PIC
+
+; RUN: ld.lld %t.o -o %t-out -save-temps -r -mllvm -relocation-model=static
+; RUN: llvm-readobj -r %t-out.lto.o | FileCheck %s --check-prefix=STATIC
+
+
 ; PIC: R_X86_64_REX_GOTPCRELX foo
 ; STATIC: R_X86_64_PC32 foo