Re: [C PATCH] Drop qualifiers during lvalue conversion

["Uecker, Martin" <Martin.Uecker@med.uni-goettingen.de>]

Am Montag, den 23.11.2020, 14:55 +0100 schrieb Christophe Lyon:
> Hi,
> 
> 
> On Thu, 19 Nov 2020 at 07:34, Uecker, Martin
> <Martin.Uecker@med.uni-goettingen.de> wrote:
> > 
> > 
> > Here is another version of the patch. The
> > only difference is the additional the check
> > using 'tree_ssa_useless_type_conversion'.
> > 
> > 
> > Best,
> > Martin
> > 
> > 
> > 
> > 
> >     C: Drop qualifiers during lvalue conversion. PR97702
> > 
> >     2020-11-XX  Martin Uecker  <muecker@gwdg.de>
> > 
> >     gcc/
> >             * gcc/gimplify.c (gimplify_modify_expr_rhs): Optimizie
> >             NOP_EXPRs that contain compound literals.
> > 
> >     gcc/c/
> >             * c-typeck.c (convert_lvalue_to_rvalue): Drop
> > qualifiers.
> > 
> >     gcc/testsuite/
> >             * gcc.dg/cond-constqual-1.c: Adapt test.
> >             * gcc.dg/lvalue-11.c: New test.
> >             * gcc.dg/pr60195.c: Add warning.
> > 
> > 
> > 
> 
> This patch causes a regression on arm:
> FAIL: gcc.dg/fixed-point/struct-union.c (test for excess errors)
> Excess errors:
> /gcc/testsuite/gcc.dg/fixed-point/struct-union.c:60:8: warning: value
> computed is not used [-Wunused-value]
> /gcc/testsuite/gcc.dg/fixed-point/struct-union.c:61:9: warning: value
> computed is not used [-Wunused-value]
> 
> The test in question lines 60-61 are:
>   /* Test assignment to volatile structure members.  */
>   sv.f = 0.06r;
>   sv.lf = 0.07lr;
> 
> so it seems these assignments are now illegally removed.
> 
> Can you check?

Must be some kind of strange interaction with _Fract.
I am not yet sure why this happens...

Best,
Martin


> Thanks,
> 
> Christophe
>
> > 
> > diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c
> > index 413109c916c..286f3d9cd6c 100644
> > --- a/gcc/c/c-typeck.c
> > +++ b/gcc/c/c-typeck.c
> > @@ -2080,6 +2080,9 @@ convert_lvalue_to_rvalue (location_t loc,
> > struct c_expr exp,
> >      exp = default_function_array_conversion (loc, exp);
> >    if (!VOID_TYPE_P (TREE_TYPE (exp.value)))
> >      exp.value = require_complete_type (loc, exp.value);
> > +  if (convert_p && !error_operand_p (exp.value)
> > +      && (TREE_CODE (TREE_TYPE (exp.value)) != ARRAY_TYPE))
> > +    exp.value = convert (build_qualified_type (TREE_TYPE
> > (exp.value), TYPE_UNQUALIFIED),
> > exp.value);
> >    if (really_atomic_lvalue (exp.value))
> >      {
> >        vec<tree, va_gc> *params;
> > diff --git a/gcc/gimplify.c b/gcc/gimplify.c
> > index 2566ec7f0af..fd0b5202b45 100644
> > --- a/gcc/gimplify.c
> > +++ b/gcc/gimplify.c
> > @@ -5518,6 +5518,19 @@ gimplify_modify_expr_rhs (tree *expr_p, tree
> > *from_p, tree *to_p,
> >             return GS_OK;
> >           }
> > 
> > +       case NOP_EXPR:
> > +         /* Pull out compound literal expressions from a NOP_EXPR.
> > +            Those are created in the C FE to drop qualifiers
> > during
> > +            lvalue conversion.  */
> > +         if ((TREE_CODE (TREE_OPERAND (*from_p, 0)) ==
> > COMPOUND_LITERAL_EXPR)
> > +             && tree_ssa_useless_type_conversion (*from_p))
> > +           {
> > +             *from_p = TREE_OPERAND (*from_p, 0);
> > +             ret = GS_OK;
> > +             changed = true;
> > +           }
> > +         break;
> > +
> >         case COMPOUND_LITERAL_EXPR:
> >           {
> >             tree complit = TREE_OPERAND (*expr_p, 1);
> > diff --git a/gcc/testsuite/gcc.dg/cond-constqual-1.c
> > b/gcc/testsuite/gcc.dg/cond-constqual-1.c
> > index 3354c7214a4..b5a09cb0038 100644
> > --- a/gcc/testsuite/gcc.dg/cond-constqual-1.c
> > +++ b/gcc/testsuite/gcc.dg/cond-constqual-1.c
> > @@ -11,5 +11,5 @@ test (void)
> >    __typeof__ (1 ? foo (0) : 0) texpr;
> >    __typeof__ (1 ? i : 0) texpr2;
> >    texpr = 0;  /* { dg-bogus "read-only variable" "conditional
> > expression with call to const
> > function" } */
> > -  texpr2 = 0; /* { dg-error "read-only variable" "conditional
> > expression with const variable" } */
> > +  texpr2 = 0; /* { dg-bogus "read-only variable" "conditional
> > expression with const variable" } */
> >  }
> > diff --git a/gcc/testsuite/gcc.dg/lvalue-11.c
> > b/gcc/testsuite/gcc.dg/lvalue-11.c
> > new file mode 100644
> > index 00000000000..45a97d86890
> > --- /dev/null
> > +++ b/gcc/testsuite/gcc.dg/lvalue-11.c
> > @@ -0,0 +1,46 @@
> > +/* test that lvalue conversions drops qualifiers, Bug 97702 */
> > +/* { dg-do compile } */
> > +/* { dg-options "" } */
> > +
> > +
> > +void f(void)
> > +{
> > + const int j;
> > + typeof((0,j)) i10; i10 = j;;
> > + typeof(+j) i11; i11 = j;;
> > + typeof(-j) i12; i12 = j;;
> > + typeof(1?j:0) i13; i13 = j;;
> > + typeof((int)j) i14; i14 = j;;
> > + typeof((const int)j) i15; i15 = j;;
> > +}
> > +
> > +void g(void)
> > +{
> > + volatile int j;
> > + typeof((0,j)) i21; i21 = j;;
> > + typeof(+j) i22; i22 = j;;
> > + typeof(-j) i23; i23 = j;;
> > + typeof(1?j:0) i24; i24 = j;;
> > + typeof((int)j) i25; i25 = j;;
> > + typeof((volatile int)j) i26; i26 = j;;
> > +}
> > +
> > +void h(void)
> > +{
> > + _Atomic int j;
> > + typeof((0,j)) i32; i32 = j;;
> > + typeof(+j) i33; i33 = j;;
> > + typeof(-j) i34; i34 = j;;
> > + typeof(1?j:0) i35; i35 = j;;
> > + typeof((int)j) i36; i36 = j;;
> > + typeof((_Atomic int)j) i37; i37 = j;;
> > +}
> > +
> > +void e(void)
> > +{
> > + int* restrict j;
> > + typeof((0,j)) i43; i43 = j;;
> > + typeof(1?j:0) i44; i44 = j;;
> > + typeof((int*)j) i45; i45 = j;;
> > + typeof((int* restrict)j) i46; i46 = j;;
> > +}
> > diff --git a/gcc/testsuite/gcc.dg/pr60195.c
> > b/gcc/testsuite/gcc.dg/pr60195.c
> > index 0a50a30be25..8eccf7f63ad 100644
> > --- a/gcc/testsuite/gcc.dg/pr60195.c
> > +++ b/gcc/testsuite/gcc.dg/pr60195.c
> > @@ -15,7 +15,7 @@ atomic_int
> >  fn2 (void)
> >  {
> >    atomic_int y = 0;
> > -  y;
> > +  y;           /* { dg-warning "statement with no effect" } */
> >    return y;
> >  }
> >