[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
llvm-svn: 355743
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index 77443b6..1bae6d8 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -11131,6 +11131,7 @@
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;
@@ -11771,6 +11772,7 @@
const Expr *This) const {
Expr::EvalStatus Status;
EvalInfo Info(Ctx, Status, EvalInfo::EM_ConstantExpressionUnevaluated);
+ Info.InConstantContext = true;
LValue ThisVal;
const LValue *ThisPtr = nullptr;
@@ -11854,6 +11856,7 @@
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;