Fix llvm-assertion: don't load ghost types

As I understand it, LLVM doesn't support 0-sized structs (ghost types),
which julia makes significant use of. This fixes an incorrect behavior
in the julia compiler accidentally attempting to instantiate such
0-sized structs.

When using a debug build of LLVM, this fails with an assertion error,
but failed silently on standard LLVM.

src/intrinsics.cpp

@@ -600,8 +600,13 @@ static jl_cgval_t emit_pointerref(jl_codectx_t &ctx, jl_cgval_t *argv)
  bool isboxed;
  Type *ptrty = julia_type_to_llvm(ety, &isboxed);
  assert(!isboxed);
- Value *thePtr = emit_unbox(ctx, ptrty->getPointerTo(), e, e.typ);
- return typed_load(ctx, thePtr, im1, ety, tbaa_data, nullptr, true, align_nb);
+ if (!type_is_ghost(ptrty)) {
+ Value *thePtr = emit_unbox(ctx, ptrty->getPointerTo(), e, e.typ);
+ return typed_load(ctx, thePtr, im1, ety, tbaa_data, nullptr, true, align_nb);
+ }
+ else {
+ return mark_julia_const(((jl_datatype_t*)ety)->instance);
+ }
  }
 }
 
@@ -663,8 +668,12 @@ static jl_cgval_t emit_pointerset(jl_codectx_t &ctx, jl_cgval_t *argv)
  bool isboxed;
  Type *ptrty = julia_type_to_llvm(ety, &isboxed);
  assert(!isboxed);
- thePtr = emit_unbox(ctx, ptrty->getPointerTo(), e, e.typ);
- typed_store(ctx, thePtr, im1, x, ety, tbaa_data, nullptr, nullptr, align_nb);
+ if (!type_is_ghost(ptrty)) {
+ thePtr = emit_unbox(ctx, ptrty->getPointerTo(), e, e.typ);
+ typed_store(ctx, thePtr, im1, x, ety, tbaa_data, nullptr, nullptr, align_nb);
+ } else {
+ return e;
+ }
  }
  return mark_julia_type(ctx, thePtr, false, aty);
 }