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" }
}
}
