Ping.
On Wed, Jul 17, 2019 at 04:05:24PM -0400, Marek Polacek wrote:
> On Wed, Jul 03, 2019 at 01:57:06PM -0400, Jason Merrill wrote:
> > On 7/3/19 10:13 AM, Marek Polacek wrote:
> > > On Sat, Jun 22, 2019 at 11:28:36PM -0400, Jason Merrill wrote:
> > > > On 6/13/19 5:03 PM, Marek Polacek wrote:
> > > > > Case values are converted constant expressions, so narrowing
> > > > > conversion is not
> > > > > permitted. This patch adds detecting narrowing to case_conversion;
> > > > > it's a
> > > > > handy spot because we have both the value and the (adjusted) type of
> > > > > the
> > > > > condition.
> > > >
> > > > Is there a reason not to use build_converted_constant_expr?
> > >
> > > The function comment says "Note that if TYPE and VALUE are already
> > > integral
> > > we don't really do the conversion because the language-independent
> > > warning/optimization code will work better that way" so I avoided adding
> > > any
> > > conversions.
> >
> > > What I could do is to, instead of calling check_narrowing, call
> > > build_converted_constant_expr (type, value, tf_warning_or_error);
> > > and not use its result, but I'm not sure what the benefits would be.
> >
> > I was thinking about using it instead of the current
> > perform_implicit_conversion_flags, so we get the somewhat different
> > constraints on the conversion. And then it becomes simpler to use it
> > unconditionally but throw the result away in the easy case.
>
> Ah, I see. So something like this?
>
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
>
> 2019-07-17 Marek Polacek <pola...@redhat.com>
>
> PR c++/90805 - detect narrowing in case values.
> * decl.c (case_conversion): Detect narrowing in case values.
>
> * c-c++-common/pr89888.c: Update expected dg-error.
> * g++.dg/cpp0x/Wnarrowing17.C: New test.
> * g++.dg/cpp0x/enum28.C: Update expected dg-error.
>
> diff --git gcc/cp/decl.c gcc/cp/decl.c
> index dbcf681c783..2d3ffdfbb54 100644
> --- gcc/cp/decl.c
> +++ gcc/cp/decl.c
> @@ -3630,16 +3630,23 @@ case_conversion (tree type, tree value)
>
> value = mark_rvalue_use (value);
>
> + if (INTEGRAL_OR_UNSCOPED_ENUMERATION_TYPE_P (type))
> + type = type_promotes_to (type);
> +
> + tree ovalue = value;
> + /* The constant-expression VALUE shall be a converted constant expression
> + of the adjusted type of the switch condition, which doesn't allow
> + narrowing conversions. */
> + value = build_converted_constant_expr (type, value, tf_warning_or_error);
> +
> if (cxx_dialect >= cxx11
> && (SCOPED_ENUM_P (type)
> - || !INTEGRAL_OR_UNSCOPED_ENUMERATION_TYPE_P (TREE_TYPE (value))))
> - {
> - if (INTEGRAL_OR_UNSCOPED_ENUMERATION_TYPE_P (type))
> - type = type_promotes_to (type);
> - value = (perform_implicit_conversion_flags
> - (type, value, tf_warning_or_error,
> - LOOKUP_IMPLICIT | LOOKUP_NO_NON_INTEGRAL));
> - }
> + || !INTEGRAL_OR_UNSCOPED_ENUMERATION_TYPE_P (TREE_TYPE (ovalue))))
> + /* Use the converted value. */;
> + else
> + /* The already integral case. */
> + value = ovalue;
> +
> return cxx_constant_value (value);
> }
>
> diff --git gcc/testsuite/c-c++-common/pr89888.c
> gcc/testsuite/c-c++-common/pr89888.c
> index d9e11d6f26a..f14881ca052 100644
> --- gcc/testsuite/c-c++-common/pr89888.c
> +++ gcc/testsuite/c-c++-common/pr89888.c
> @@ -11,8 +11,8 @@ foo (unsigned char x)
> {
> case -1: y = -1; break; /* { dg-message "previously
> used here" } */
> /* { dg-warning "case label
> value is less than minimum value for type" "" { target *-*-* } .-1 } */
> - case 0xffffffff: y = 0xffffffff; break; /* { dg-error "duplicate case
> value" } */
> - case ~0U: y = ~0U; break; /* { dg-error
> "duplicate case value" } */
> + case 0xffffffff: y = 0xffffffff; break; /* { dg-error "duplicate case
> value|narrowing" } */
> + case ~0U: y = ~0U; break; /* { dg-error
> "duplicate case value|narrowing" } */
> }
> }
>
> diff --git gcc/testsuite/g++.dg/cpp0x/Wnarrowing17.C
> gcc/testsuite/g++.dg/cpp0x/Wnarrowing17.C
> new file mode 100644
> index 00000000000..064de531cb3
> --- /dev/null
> +++ gcc/testsuite/g++.dg/cpp0x/Wnarrowing17.C
> @@ -0,0 +1,19 @@
> +// PR c++/90805 - detect narrowing in case values.
> +// { dg-do compile { target c++11 } }
> +
> +void f(int i, char c, unsigned u)
> +{
> + switch (i)
> + {
> + case 2149056512u:; // { dg-error "narrowing conversion of .2149056512.
> from .unsigned int. to .int." }
> + case (long long int) 1e10:; // { dg-error "narrowing conversion of
> .10000000000. from .long long int. to .int." }
> + // { dg-warning "overflow in conversion" "overflow" { target *-*-* } .-1
> }
> + }
> +
> + switch (c)
> + // No narrowing, the adjusted type is int.
> + case 300:; // { dg-warning "exceeds maximum value for type" }
> +
> + switch (u)
> + case -42:; // { dg-error "narrowing conversion of .-42. from .int. to
> .unsigned int." }
> +}
> diff --git gcc/testsuite/g++.dg/cpp0x/enum28.C
> gcc/testsuite/g++.dg/cpp0x/enum28.C
> index 3967699dd03..bfebde57cb3 100644
> --- gcc/testsuite/g++.dg/cpp0x/enum28.C
> +++ gcc/testsuite/g++.dg/cpp0x/enum28.C
> @@ -7,11 +7,11 @@ void f(int i)
> {
> switch (i)
> {
> - case 1.0:; // { dg-error "could not convert" }
> + case 1.0:; // { dg-error "could not convert|conversion from" }
> }
>
> switch (i)
> {
> - case g():; // { dg-error "could not convert" }
> + case g():; // { dg-error "could not convert|conversion from" }
> }
> }
Marek
