[llvm-bugs] [Bug 47338] New: "fragment covers entire variable" verifier error in Windows thinlto builds

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https://bugs.llvm.org/show_bug.cgi?id=47338

            Bug ID: 47338
           Summary: "fragment covers entire variable" verifier error in
                    Windows thinlto builds
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: akhuang at google.com
                CC: llvm-bugs at lists.llvm.org

We ran into this error in chromium thinlto builds on windows, with
-debug-info-kind=constructor enabled. With -debug-info-kind=constructor, more
class types are not defined in the debug info and don't have sizes.

Here's a reduced repro that shows the fragment being emitted (for C.a_, I
think). The verifier error only happens with thinlto, because the assert isn't
called if the var size doesn't exist (during thinlto the complete type is
probably pulled from somewhere else).

$ cat t.cpp
// With ctor homing, this struct is not defined in the debug info, so it
doesn't have a size.
struct A {
  A();
  int i;
};
struct B {
  virtual void f();
};
struct C {
  C(A a, B a) : a_(a), b_(b) {}
  A a_;
  B b_;
};

C CodeFactory() {
  A a;
  return C(a, B{});
}
$ clang -cc1 -triple i386-windows-msvc -O2 -debug-info-kind=constructor -o t.ll
t.cpp


I fixed a similar issue in `transferSRADebugInfo` by not getting the size from
the DI type (https://reviews.llvm.org/D85572), but not sure if I can do the
same thing here.

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