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

[Aaron Ballman]

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. 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}}
>  }
>
>
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