[Builtins] Implement __builtin_is_constant_evaluated for use in C++2a
Summary:
This patch implements `__builtin_is_constant_evaluated` as specifier by [P0595R2](https://wg21.link/p0595r2). It is built on the back of Bill Wendling's work for `__builtin_constant_p()`.
More tests to come, but early feedback is appreciated.
I plan to implement warnings for common mis-usages like those belowe in a following patch:
```
void foo(int x) {
if constexpr (std::is_constant_evaluated())) { // condition is always `true`. Should use plain `if` instead.
foo_constexpr(x);
} else {
foo_runtime(x);
}
}
```
Reviewers: rsmith, MaskRay, bruno, void
Reviewed By: rsmith
Subscribers: dexonsmith, zoecarver, fdeazeve, kristina, cfe-commits
Differential Revision: https://reviews.llvm.org/D55500
llvm-svn: 359067
diff --git a/clang/lib/CodeGen/CGDecl.cpp b/clang/lib/CodeGen/CGDecl.cpp
index aea99dbb..a5c0224 100644
--- a/clang/lib/CodeGen/CGDecl.cpp
+++ b/clang/lib/CodeGen/CGDecl.cpp
@@ -1783,7 +1783,8 @@
}
llvm::Constant *constant = nullptr;
- if (emission.IsConstantAggregate || D.isConstexpr()) {
+ if (emission.IsConstantAggregate || D.isConstexpr() ||
+ D.isUsableInConstantExpressions(getContext())) {
assert(!capturedByInit && "constant init contains a capturing block?");
constant = ConstantEmitter(*this).tryEmitAbstractForInitializer(D);
if (constant && trivialAutoVarInit !=