[Bug middle-end/102285] New flag -ftrivial-auto-var-init=zero causes crash in pr82421.c

["rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102285

--- Comment #20 from rguenther at suse dot de <rguenther at suse dot de> ---
On Fri, 1 Oct 2021, qinzhao at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102285
> 
> --- Comment #18 from qinzhao at gcc dot gnu.org ---
> (In reply to Richard Biener from comment #13)
> > We could try sth like the following which should cover this testcase and
> > also hopefully doesn't break anything else.
> > 
> > diff --git a/gcc/expr.c b/gcc/expr.c
> > index e0bcbccd905..ab3b5b26c20 100644
> > --- a/gcc/expr.c
> > +++ b/gcc/expr.c
> > @@ -5322,7 +5322,7 @@ non_mem_decl_p (tree base)
> >  /* Returns true if REF refers to an object that does not
> >     reside in memory and has non-BLKmode.  */
> >  
> > -static inline bool
> > +bool
> >  mem_ref_refers_to_non_mem_p (tree ref)
> >  {
> >    tree base;
> > diff --git a/gcc/expr.h b/gcc/expr.h
> > index 94a85b40dca..85650e96834 100644
> > --- a/gcc/expr.h
> > +++ b/gcc/expr.h
> > @@ -346,4 +346,6 @@ extern void expand_operands (tree, tree, rtx, rtx*, rtx*,
> >  /* Return an rtx for the size in bytes of the value of an expr.  */
> >  extern rtx expr_size (tree);
> >  
> > +extern bool mem_ref_refers_to_non_mem_p (tree ref);
> > +
> >  #endif /* GCC_EXPR_H */
> > diff --git a/gcc/internal-fn.c b/gcc/internal-fn.c
> > index 8312d08aab2..c1d23dfd21e 100644
> > --- a/gcc/internal-fn.c
> > +++ b/gcc/internal-fn.c
> > @@ -3015,8 +3015,10 @@ expand_DEFERRED_INIT (internal_fn, gcall *stmt)
> >      reg_lhs = true;
> >    else
> >      {
> > -      rtx tem = expand_expr (lhs, NULL_RTX, VOIDmode, EXPAND_WRITE);
> > -      reg_lhs = !MEM_P (tem);
> > +      tree lhs_base = lhs;
> > +      while (handled_component_p (lhs_base))
> > +       lhs_base = TREE_OPERAND (lhs_base, 0);
> > +      reg_lhs = mem_refers_to_non_mem_p (lhs_base);
> >      }
> >  
> >    if (!reg_lhs)
> 
> I tried the above patch, it even doesn't work for this testing case. 
> After the patch, this call to .DEFERRED_INIT will be expanded through REG path,
> however, the existing problem in the LHS IR broke the "expand_assignment" too. 
> so

I see.

> , I still think that the root cause is the IR for LHS of the following 
call
> to .DEFERRED_INIT is not correct:
>
> MEM[(int[0:D.1993] *)&fb.3] = .DEFERRED_INIT (16, 2, 1);
> 
> the LHS is: MEM[(int[0:D.1993] *)&fb.3]
> 
> this is the MEM_REF, whose base address is a ADDR_EXPR of a VAR_DECL, however,
> this VAR_DECL is not addressable, will be in REG. this is conflicting: how can
> a variable that in a REG be address taken?

It doesn't have its address taken - the ADDR_EXPR is artificial when
at the base of a MEM_REF.

Let me thake this bug then.