[LLVMbugs] [Bug 17111] New: missing nop after branch

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=17111

            Bug ID: 17111
           Summary: missing nop after branch
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: PowerPC
          Assignee: unassignedbugs at nondot.org
          Reporter: nlewycky at google.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Testcase:

  class Base {
  protected:
    Base() {}

  public:
    virtual ~Base();
    virtual void BaseMethod() {}
  };

  struct Derived : public Base {
    ~Derived() {
      DerivedMethod();
    }

    void DerivedMethod();

    virtual void BaseMethod();
  };

  void Derived::DerivedMethod() {}
  void Derived::BaseMethod() {}

The bug is in the assembly generated for the destructor. Here's a snippet:

  .Ltmp4:
         std 5, 120(31)
         bl _ZN7Derived13DerivedMethodEv
  .Ltmp5:
         b .LBB4_1

That doesn't leave enough space for the linker to insert the TOC reload when
resolving the R_PPC64_REL24 relocation. There needs to be a nop after the
branch+link instruction.

Reproduce with:

  clang -target powerpc64-pc-linux-gnu -fpic testcase.cc -S -o -

Ultimately the symptom is a failure when linking:

  error: call lacks nop, can't restore toc; recompile with -fPIC

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