[Mesa-dev] [PATCH 2/4] compiler: avoid 'unused variable' and 'may be used uninitialized' warnings

[Eric Engestrom]

On Friday, 2018-11-09 16:15:12 +0200, andrey simiklit wrote:
> Hello,
> 
> Thanks for review.
> Please find my comments below:
> 
> On Fri, Nov 9, 2018 at 2:52 PM Eric Engestrom <eric.engestrom at intel.com>
> wrote:
> 
> > On Tuesday, 2018-09-11 15:42:05 +0300, asimiklit.work at gmail.com wrote:
> > > From: Andrii Simiklit <andrii.simiklit at globallogic.com>
> > >
> > > 1. nir/nir_lower_vars_to_ssa.c:691:21: warning:
> > >        unused variable ‘var’
> > >        nir_variable *var = path->path[0]->var;
> > >
> > > 2. nir_types.cpp:558:31: warning:
> > >     ‘elem_align’ may be used uninitialized in this function
> > >            unsigned elem_size, elem_align;
> > >    nir_types.cpp:558:20: warning:
> > >    ‘elem_size’ may be used uninitialized in this function
> > >            unsigned elem_size, elem_align;
> > >
> > > Signed-off-by: Andrii Simiklit <andrii.simiklit at globallogic.com>
> > > ---
> > >  src/compiler/nir/nir_lower_vars_to_ssa.c | 2 +-
> > >  src/compiler/nir_types.cpp               | 4 ++--
> > >  2 files changed, 3 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/src/compiler/nir/nir_lower_vars_to_ssa.c
> > b/src/compiler/nir/nir_lower_vars_to_ssa.c
> > > index cd679be..96de261 100644
> > > --- a/src/compiler/nir/nir_lower_vars_to_ssa.c
> > > +++ b/src/compiler/nir/nir_lower_vars_to_ssa.c
> > > @@ -688,7 +688,7 @@ nir_lower_vars_to_ssa_impl(nir_function_impl *impl)
> > >        nir_deref_path *path = &node->path;
> > >
> > >        assert(path->path[0]->deref_type == nir_deref_type_var);
> > > -      nir_variable *var = path->path[0]->var;
> > > +      MAYBE_UNUSED nir_variable *var = path->path[0]->var;
> > >
> > >        /* We don't build deref nodes for non-local variables */
> > >        assert(var->data.mode == nir_var_local);
> >
> > Sure, or you could simply remove the single-use extra local variable and
> > just fold it into the assert :)
> >
> 
> I agree,will fix :)
> 
> 
> >
> > > diff --git a/src/compiler/nir_types.cpp b/src/compiler/nir_types.cpp
> > > index d24f094..d39d87b 100644
> > > --- a/src/compiler/nir_types.cpp
> > > +++ b/src/compiler/nir_types.cpp
> > > @@ -542,7 +542,7 @@ glsl_get_natural_size_align_bytes(const struct
> > glsl_type *type,
> > >     }
> > >
> > >     case GLSL_TYPE_ARRAY: {
> > > -      unsigned elem_size, elem_align;
> > > +      unsigned elem_size = 0, elem_align = 0;
> >
> > Not really keen on these ones; it looks like your compiler is ignoring the
> > unreachable() in glsl_get_natural_size_align_bytes() and mis-computing the
> > possible code-paths, resulting in it wrongly printing a warning.
> >
> 
> You are right when I added the 'default:' case to the switch the warning is
> disappeared:
> 
> case GLSL_TYPE_INTERFACE:
> case GLSL_TYPE_FUNCTION:
> +default:
>    unreachable("type does not have a natural size");
> 
> What do you think about such solution? Is it acceptable for you?

Is there any possible value of `enum glsl_base_type` that is not handled
by the switch? If so, they should be added. Otherwise, this is
a compiler bug, not a code bug :)

> 
> 
> > I'd prefer to keep these two hunks as is, so that real issue in
> > glsl_get_natural_size_align_bytes() would get flagged appropriately.
> >
> > >        glsl_get_natural_size_align_bytes(type->fields.array,
> > >                                          &elem_size, &elem_align);
> > >        *align = elem_align;
> > > @@ -554,7 +554,7 @@ glsl_get_natural_size_align_bytes(const struct
> > glsl_type *type,
> > >        *size = 0;
> > >        *align = 0;
> > >        for (unsigned i = 0; i < type->length; i++) {
> > > -         unsigned elem_size, elem_align;
> > > +         unsigned elem_size = 0, elem_align = 0;
> > >
> >  glsl_get_natural_size_align_bytes(type->fields.structure[i].type,
> > >                                             &elem_size, &elem_align);
> > >           *align = MAX2(*align, elem_align);
> > > --
> > > 2.7.4
> > >
> > > _______________________________________________
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> >