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From: "simon.willcocks at gmx dot de" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug inline-asm/101422] register variable uninitialised before
 passing to asm
Date: Thu, 15 Jul 2021 11:41:20 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101422

--- Comment #8 from Simon Willcocks <simon.willcocks at gmx dot de> ---
(In reply to Andrew Pinski from comment #4)
> (In reply to Simon Willcocks from comment #2)
> > That's not an accurate description of the problem; the value of the var=
iable
> > is being passed, not its address. As a register variable, it doesn't ha=
ve an
> > address.
>=20
> It is the address of the array that is being passed (I was copying and
> pasting from another bug).
> register uint32_t *cap_and_join asm( "r5" ) =3D cap_and_join_style;
> Is the same as:
> register uint32_t *cap_and_join asm( "r5" ) =3D &cap_and_join_style[0];
>=20
> Because array decays to pointers :).

And, of course, I later came up against this precise problem, at least I kn=
ew
what I was looking for, and thanks to you, how to fix it. The final solutio=
n is
as follows. I really think that passing a pointer type into an asm should
indicate that the object pointed to is used, though.

void Draw_Stroke( uint32_t *path )=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20
{=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20
  // Keep this declaration before the first register variable declaration, =
or=20=20=20
  // -Os will cause the compiler to forget the preceding registers.=20=20=
=20=20=20=20=20=20=20=20=20=20=20
  // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101422=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20
  uint32_t cap_and_join_style[5] =3D  { 0x00000001 }; // Round joints=20=20=
=20=20=20=20=20=20=20=20=20=20=20

  register uint32_t *draw_path asm( "r0" ) =3D path;=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20
  register uint32_t fill_style asm( "r1" ) =3D 0x3f;=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20
  register uint32_t *matrix asm( "r2" ) =3D 0;=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20
  register uint32_t flatness asm( "r3" ) =3D 0;=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20
  register uint32_t thickness asm( "r4" ) =3D 8;=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20
  register uint32_t *cap_and_join asm( "r5" ) =3D cap_and_join_style;=20=20=
=20=20=20=20=20=20=20=20=20=20=20
  register uint32_t dashes asm( "r6" ) =3D 0;=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20
  asm ( "swi 0x60704" :=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20
        : "r" (draw_path)=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20
        , "r" (fill_style)=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20
        , "r" (matrix)=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20
        , "r" (flatness)=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20
        , "r" (thickness)=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20
        , "r" (cap_and_join)=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20
        , "r" (dashes)=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20
        , "m" (cap_and_join_style) ); // Without this, array is not initial=
ised=20
}

I wanted to correct the record and thank you (both). I'll shut up, now.=