Re: gcc torture test pr52286.c

[Michael Matz <matz at suse dot de>]

Hi,

On Mon, 28 Aug 2017, Paul S wrote:

> I've ported gcc to a 16 bit CPU and have all torture tests passing bar one,
> pr52286.c
> 
> The offending lines of code are
> 
>   long a, b = 0;
>   asm ("" : "=r" (a) : "0" (0));
> 
> 
> which should cause zero to be assigned to the "a" SI sized variable.
> 
> Inspecting the generated code revealed that zero was only being assigned to
> the lower 16 bit half of "a".
> 
> ld    r2,0
> 
> I changed the inline asm statement to
> 
>   asm ("" : "=r" (a) : "0" (0L));

I think this really is the right fix for this testcase.  The testcase was 
obviously developed for sizeof(int)>2 targets.  The involved constant 
doesn't fit into int on those, but the #ifdef case for <=2 targets seems 
to have been an afterthought.  The asm would have needed the adjustment 
that you had to do now.

> so it seems that the "0" constraint on the input operand is affecting 
> the inferred mode of the output register operand ?

Or put another way, the required longness (two regs) of the output 
constraints isn't reflected back into the input constraint, yes.  For 
matching constraints the promoted types of the operands need to match, but 
nothing checks this :-/


Ciao,
Michael.