On Wed, Jun 10, 2020 at 10:24:59AM +0200, Martin Liška wrote:
> > > This doesn't look correct to me.
> > > I'd think the first adjust_address should be
> > > mem = adjust_address (mem, ptr_mode, offset);
> > > which will give you a MEM with ptr_mode which has SavedFlagPtr(FakeStack)
> > > address, i.e. *SavedFlagPtr(FakeStack).
> > > Next, you want to load that into some temporary, so e.g.
> > > rtx addr = gen_reg_rtx (ptr_mode);
> > > emit_move_insn (addr, mem);
> > > next you need to convert that ptr_mode to Pmode if needed, so something
> > > like
> > > addr = convert_memory_address (Pmode, addr);
> > > and finally:
> > > mem = gen_rtx_MEM (QImode, addr);
> > > emit_move_insn (mem, const0_rtx);
> > > Completely untested.
> >
> > This is not correct. With your suggestion I have:
> >
> > int foo(int index)
> > {
> > int a[100];
> > return a[index];
> > }
> >
> > $ diff -u before.s after.s
> > --- before.s 2020-06-01 15:15:22.634337654 +0200
> > +++ after.s 2020-06-01 15:16:32.205711511 +0200
> > @@ -81,8 +81,7 @@
> > movq %rdi, 2147450920(%rax)
> > movq %rsi, 2147450928(%rax)
> > movq %rdi, 2147450936(%rax)
> > - movq 504(%rbx), %rax
> > - movb $0, (%rax)
> > + movb $0, 504(%rbx)
> > jmp .L3
> > .L2:
> > movq $0, 2147450880(%rax)
> >
> > There's missing one level of de-reference. Looking at clang:
> >
> > movq %rsi, 2147450928(%rax)
> > movq %rdi, 2147450936(%rax)
> > movq 504(%rbx), %rax
> > movb $0, (%rax)
> > jmp .L3
> > .L2:
> >
> > It does the same as my patch.
>
> Jakub?
Even if so, just add that another level of indirection where it belongs,
but as I said, what you posted didn't feel right. E.g. we just shouldn't reuse
MEMs (even after adjusting them) from different indirection levels because
we risk some attributes (alias set, MEM_EXPR, whatever else) will stay
around from the different indirection level.
Jakub
