r223184 - PR21706: -Wunsequenced was missing warnings when leaving a sequenced region that contained side effects.

[Richard Smith]

On Wed, Dec 3, 2014 at 6:52 AM, Aaron Ballman <aaron at aaronballman.com>
wrote:

> On Tue, Dec 2, 2014 at 8:05 PM, Richard Smith
> <richard-llvm at metafoo.co.uk> wrote:
> > Author: rsmith
> > Date: Tue Dec  2 19:05:50 2014
> > New Revision: 223184
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=223184&view=rev
> > Log:
> > PR21706: -Wunsequenced was missing warnings when leaving a sequenced
> region that contained side effects.
>
> This doesn't seem to account for unevaluated contexts.


This is a pre-existing issue that was merely exposed in more cases by this
change; we used to warn on, for instance,

  int n;
  int k = ++n + _Generic(++n, default: 0);

Fixed in r223266.

For instance, I
> now get a false-positive with code like:
>
> void blah(int a);
>
> #define GenTest(x) _Generic(x, default : blah)(x)
>
> void f(void) {
>   int i = 0;
>   GenTest(++i);
> }
>
> ~Aaron
>
> >
> > Modified:
> >     cfe/trunk/lib/Sema/SemaChecking.cpp
> >     cfe/trunk/test/Sema/warn-unsequenced.c
> >
> > Modified: cfe/trunk/lib/Sema/SemaChecking.cpp
> > URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaChecking.cpp?rev=223184&r1=223183&r2=223184&view=diff
> >
> ==============================================================================
> > --- cfe/trunk/lib/Sema/SemaChecking.cpp (original)
> > +++ cfe/trunk/lib/Sema/SemaChecking.cpp Tue Dec  2 19:05:50 2014
> > @@ -7014,11 +7014,12 @@ class SequenceChecker : public Evaluated
> >        Self.ModAsSideEffect = &ModAsSideEffect;
> >      }
> >      ~SequencedSubexpression() {
> > -      for (unsigned I = 0, E = ModAsSideEffect.size(); I != E; ++I) {
> > -        UsageInfo &U = Self.UsageMap[ModAsSideEffect[I].first];
> > -        U.Uses[UK_ModAsSideEffect] = ModAsSideEffect[I].second;
> > -        Self.addUsage(U, ModAsSideEffect[I].first,
> > -                      ModAsSideEffect[I].second.Use, UK_ModAsValue);
> > +      for (auto MI = ModAsSideEffect.rbegin(), ME =
> ModAsSideEffect.rend();
> > +           MI != ME; ++MI) {
> > +        UsageInfo &U = Self.UsageMap[MI->first];
> > +        auto &SideEffectUsage = U.Uses[UK_ModAsSideEffect];
> > +        Self.addUsage(U, MI->first, SideEffectUsage.Use, UK_ModAsValue);
> > +        SideEffectUsage = MI->second;
> >        }
> >        Self.ModAsSideEffect = OldModAsSideEffect;
> >      }
> >
> > Modified: cfe/trunk/test/Sema/warn-unsequenced.c
> > URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/warn-unsequenced.c?rev=223184&r1=223183&r2=223184&view=diff
> >
> ==============================================================================
> > --- cfe/trunk/test/Sema/warn-unsequenced.c (original)
> > +++ cfe/trunk/test/Sema/warn-unsequenced.c Tue Dec  2 19:05:50 2014
> > @@ -29,6 +29,11 @@ void test() {
> >    a = f(a++, 0); // ok
> >    a = f(++a, a++); // expected-warning {{multiple unsequenced
> modifications}}
> >
> > +  ++a + f(++a, 0); // expected-warning {{multiple unsequenced
> modifications}}
> > +  f(++a, 0) + ++a; // expected-warning {{multiple unsequenced
> modifications}}
> > +  a++ + f(a++, 0); // expected-warning {{multiple unsequenced
> modifications}}
> > +  f(a++, 0) + a++; // expected-warning {{multiple unsequenced
> modifications}}
> > +
> >    a = ++a; // expected-warning {{multiple unsequenced modifications}}
> >    a += ++a; // expected-warning {{unsequenced modification and access}}
> >
> > @@ -48,7 +53,7 @@ void test() {
> >    (1 ? a : ++a) + a; // ok
> >    (xs[5] ? ++a : ++a) + a; // FIXME: warn here
> >
> > -  (++a, xs[6] ? ++a : 0) + a; // FIXME: warn here
> > +  (++a, xs[6] ? ++a : 0) + a; // expected-warning {{unsequenced
> modification and access}}
> >
> >    // Here, the read of the fourth 'a' might happen before or after the
> write to
> >    // the second 'a'.
> > @@ -84,5 +89,5 @@ void test() {
> >
> >    (__builtin_classify_type(++a) ? 1 : 0) + ++a; // ok
> >    (__builtin_constant_p(++a) ? 1 : 0) + ++a; // ok
> > -  (__builtin_expect(++a, 0) ? 1 : 0) + ++a; // FIXME: warn here
> > +  (__builtin_expect(++a, 0) ? 1 : 0) + ++a; // expected-warning
> {{multiple unsequenced modifications}}
> >  }
> >
> >
> > _______________________________________________
> > cfe-commits mailing list
> > cfe-commits at cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
>
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