llvm-lto: default Relocation Model should be selected by the TargetMachine.

[w2yehia]

Summary

Right now, the createTargetMachine function in LTOBackend.cpp (used by llvm-lto, and other components) selects the default Relocation Model when none is specified in the module.
Other components (such as opt and llc) that construct a TargetMachine delegate the decision on the default value to the polymorphic TargetMachine's constructor.

This commit aligns llvm-lto with other components.

[daltenty]

LGTM, thanks!

Noting this is to fix assertions in llvm/test/LTO/X86/remangle_intrinsics.ll on AIX.

[fhahn]

Any chance you could add an explicit test?

[w2yehia]

@fhahn do you mean a negative test to make sure the assertion that got tripped in llvm/test/LTO/X86/remangle_intrinsics.ll does not happen anymore? Or test that llvm-lto delegates the relocation model property to the TargetMachine?

[w2yehia]

@daltenty provided a reduced testcase that would fail without this fix.

[fhahn]

In D97507#2615598, @w2yehia wrote:

@daltenty provided a reduced testcase that would fail without this fix.

Thanks!

llvm/test/tools/llvm-lto/aix.ll

4 ↗

(On Diff #329514)

this needs a "REQUIRES" line to make sure the powerpc target has been built.

[w2yehia]

llvm/test/tools/llvm-lto/aix.ll

4 ↗

(On Diff #329514)

good point, thank you.

[fhahn]

LGTM, thanks!

[aaronpuchert]

Shouldn't the test be in llvm/test/... instead of test/...? This seems like a mistake.

[w2yehia]

In D97507#2623901, @aaronpuchert wrote:

Shouldn't the test be in llvm/test/... instead of test/...? This seems like a mistake.

oops, will fix it. Thank you for pointing out.

llvm/lib/LTO/LTOBackend.cpp

 static std::unique_ptr<TargetMachine>
 createTargetMachine(const Config &Conf, const Target *TheTarget, Module &M) {
   StringRef TheTriple = M.getTargetTriple();
   SubtargetFeatures Features;
   Features.getDefaultSubtargetFeatures(Triple(TheTriple));
   for (const std::string &A : Conf.MAttrs)
     Features.AddFeature(A);
 
-  Reloc::Model RelocModel;
+  Optional<Reloc::Model> RelocModel = None;
   if (Conf.RelocModel)
     RelocModel = *Conf.RelocModel;
-  else
+  else if (M.getModuleFlag("PIC Level"))
     RelocModel =
         M.getPICLevel() == PICLevel::NotPIC ? Reloc::Static : Reloc::PIC_;
 
   Optional<CodeModel::Model> CodeModel;
   if (Conf.CodeModel)
     CodeModel = *Conf.CodeModel;
   else
     CodeModel = M.getCodeModel();

test/tools/llvm-lto/aix.ll

+; REQUIRES: powerpc-registered-target
+; RUN: llvm-as < %s > %t1
+; RUN: llvm-lto %t1 | FileCheck %s
+
+target triple = "powerpc-ibm-aix"
+
+define i32 @main() {
+entry:
+  ret i32 42
+}
+; CHECK: Wrote native object file
+