Commit 25292d1c authored by Hans Wennborg's avatar Hans Wennborg
Browse files

Merging r355743: 

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r355743 | ericwf | 2019-03-08 23:06:48 +0100 (Fri, 08 Mar 2019) | 26 lines

[8.0 Regression] Fix handling of `__builtin_constant_p` inside template arguments, enumerators, case statements, and the enable_if attribute.

Summary:
The following code is accepted by Clang 7 and prior but rejected by the upcoming 8 release and in trunk [1]

```
// error {{never produces a constant expression}}
void foo(const char* s) __attribute__((enable_if(__builtin_constant_p(*s) == false, "trap"))) {}
void test() { foo("abc"); }
```

Prior to Clang 8, the call to `__builtin_constant_p` was a constant expression returning false. Currently, it's not a valid constant expression.

The bug is caused because we failed to set `InConstantContext` when attempting to evaluate unevaluated constant expressions.

[1]  https://godbolt.org/z/ksAjmq

Reviewers: rsmith, hans, sbenza

Reviewed By: rsmith

Subscribers: kristina, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D59038
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llvm-svn: 355898
parent 60c05513

clang/lib/AST/ExprConstant.cpp

+3 −0
Original line number Diff line number Diff line
@@ -10985,6 +10985,7 @@ bool Expr::EvaluateAsConstantExpr(EvalResult &Result, ConstExprUsage Usage, 
                                  const ASTContext &Ctx) const {

  EvalInfo::EvaluationMode EM = EvalInfo::EM_ConstantExpression;

  EvalInfo Info(Ctx, Result, EM);

  Info.InConstantContext = true;

  if (!::Evaluate(Result.Val, Info, this))

    return false;
@@ -11625,6 +11626,7 @@ bool Expr::EvaluateWithSubstitution(APValue &Value, ASTContext &Ctx, 
                                    const Expr *This) const {

  Expr::EvalStatus Status;

  EvalInfo Info(Ctx, Status, EvalInfo::EM_ConstantExpressionUnevaluated);

  Info.InConstantContext = true;



  LValue ThisVal;

  const LValue *ThisPtr = nullptr;
@@ -11708,6 +11710,7 @@ bool Expr::isPotentialConstantExprUnevaluated(Expr *E, 


  EvalInfo Info(FD->getASTContext(), Status,

                EvalInfo::EM_PotentialConstantExpressionUnevaluated);

  Info.InConstantContext = true;



  // Fabricate a call stack frame to give the arguments a plausible cover story.

  ArrayRef<const Expr*> Args;

clang/test/SemaCXX/constant-expression-cxx1y.cpp

+24 −0
Original line number Diff line number Diff line
@@ -1135,3 +1135,27 @@ constexpr bool indirect_builtin_constant_p(const char *__s) { 
  return __builtin_constant_p(*__s);

}

constexpr bool n = indirect_builtin_constant_p("a");



__attribute__((enable_if(indirect_builtin_constant_p("a") == n, "OK")))

int test_in_enable_if() { return 0; }

int n2 = test_in_enable_if();



template <bool n = indirect_builtin_constant_p("a")>

int test_in_template_param() { return 0; }

int n3 = test_in_template_param();



void test_in_case(int n) {

  switch (n) {

    case indirect_builtin_constant_p("abc"):

    break;

  }

}

enum InEnum1 {

  ONE = indirect_builtin_constant_p("abc")

};

enum InEnum2 : int {

  TWO = indirect_builtin_constant_p("abc")

};

enum class InEnum3 {

  THREE = indirect_builtin_constant_p("abc")

};

clang/test/SemaCXX/enable_if.cpp

+8 −0
Original line number Diff line number Diff line
@@ -514,3 +514,11 @@ namespace TypeOfFn { 


  static_assert(is_same<__typeof__(foo)*, decltype(&foo)>::value, "");

}



namespace InConstantContext {

void foo(const char *s) __attribute__((enable_if(((void)__builtin_constant_p(*s), true), "trap"))) {}



void test() {

  InConstantContext::foo("abc");

}

} // namespace InConstantContext