Re: [PATCH] Fix PR79908

[Bill Schmidt]

On Mar 14, 2017, at 9:32 AM, Bill Schmidt <wschm...@linux.vnet.ibm.com> wrote:
> 
>> On Mar 14, 2017, at 9:25 AM, Richard Biener <richard.guent...@gmail.com> 
>> wrote:
>> 
>>>>> Better is sth like
>>>>> 
>>>>> Index: gcc/tree-stdarg.c
>>>>> ===================================================================
>>>>> --- gcc/tree-stdarg.c   (revision 246082)
>>>>> +++ gcc/tree-stdarg.c   (working copy)
>>>>> @@ -1058,7 +1058,7 @@ expand_ifn_va_arg_1 (function *fun)
>>>>>         gimplify_assign (lhs, expr, &pre);
>>>>>       }
>>>>>     else
>>>>> -         gimplify_expr (&expr, &pre, &post, is_gimple_lvalue, fb_lvalue);
>>>>> +         gimplify_expr (&expr, &pre, &post, is_gimple_val, fb_either);
>>>>> 
>>>>>     input_location = saved_location;
>>>>>     pop_gimplify_context (NULL);
>>>> 
>>>> OK, thanks for the explanation.  Unfortunately this fails bootstrap with a 
>>>> failed
>>>> assert a little later.  I'll dig further.
>>> 
>>> Looks like is_gimple_val is too restrictive for MEM_REFs, for which 
>>> is_gimple_lvalue
>>> passes.  Trying this now:
>> 
>> Hmm, it should simply gimplify to a load if it's not aggregate.  Can
>> you share a testcase
>> where it doesn't work?
> 
> Your suggestion failed bootstrap in libiberty on vprintf-support.c.  
> Compilation failed with:
> 
> /home/wschmidt/gcc/build/gcc-mainline-test2-debug/gcc/xgcc 
> -B/home/wschmidt/gcc/build/gcc-mainline-test2-debug/gcc/ 
> -B/home/wschmidt/gcc/install/gcc-mainline-test2-debug/powerpc64le-unknown-linux-gnu/bin/
>  
> -B/home/wschmidt/gcc/install/gcc-mainline-test2-debug/powerpc64le-unknown-linux-gnu/bin/
>  
> -B/home/wschmidt/gcc/install/gcc-mainline-test2-debug/powerpc64le-unknown-linux-gnu/lib/
>  -isystem 
> /home/wschmidt/gcc/install/gcc-mainline-test2-debug/powerpc64le-unknown-linux-gnu/include
>  -isystem 
> /home/wschmidt/gcc/install/gcc-mainline-test2-debug/powerpc64le-unknown-linux-gnu/sys-include
>     -c -DHAVE_CONFIG_H -g -O2 -gtoggle  -I. 
> -I/home/wschmidt/gcc/gcc-mainline-test2/libiberty/../include  -W -Wall 
> -Wwrite-strings -Wc++-compat -Wstrict-prototypes -Wshadow=local -pedantic  
> -D_GNU_SOURCE -fPIC 
> /home/wschmidt/gcc/gcc-mainline-test2/libiberty/vprintf-support.c -o 
> pic/vprintf-support.o
> 
> The initial expression being gimplified is ADDR_EXPR (VAR_DECL (ap)).  
> Gimplification
> turns this into MEM_REF (VAR_DECL (D.4274), 0), and the is_gimple_val test 
> fails on that.

Reduced test case:

typedef __builtin_va_list __gnuc_va_list;
typedef __gnuc_va_list va_list;

void
foo (va_list args)
{
  va_list ap;
  __builtin_va_copy (ap, args);
  (void)__builtin_va_arg (ap, int);
  __builtin_va_end(ap);
}