Add the diagnose_if attribute to clang.

`diagnose_if` can be used to have clang emit either warnings or errors
for function calls that meet user-specified conditions. For example:

```
constexpr int foo(int a)
  __attribute__((diagnose_if(a > 10, "configurations with a > 10 are "
                                      "expensive.", "warning")));

int f1 = foo(9);
int f2 = foo(10); // warning: configuration with a > 10 are expensive.
int f3 = foo(f2);
```

It currently only emits diagnostics in cases where the condition is
guaranteed to always be true. So, the following code will emit no
warnings:

```
constexpr int bar(int a) {
  foo(a);
  return 0;
}

constexpr int i = bar(10);
```

We hope to support optionally emitting diagnostics for cases like that
(and emitting runtime checks) in the future.

Release notes will appear shortly. :)

Differential Revision: https://reviews.llvm.org/D27424


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@291418 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 2 insertions, 0 deletions

diff --git a/include/clang/Basic/DiagnosticCommonKinds.td b/include/clang/Basic/DiagnosticCommonKinds.td
index e8180eb1db..af0612a829 100644
--- a/include/clang/Basic/DiagnosticCommonKinds.td
+++ b/include/clang/Basic/DiagnosticCommonKinds.td
@@ -161,6 +161,8 @@ def ext_old_implicitly_unsigned_long_cxx : ExtWarn<
   InGroup<CXX11Compat>;
 def ext_clang_enable_if : Extension<"'enable_if' is a clang extension">,
                           InGroup<GccCompat>;
+def ext_clang_diagnose_if : Extension<"'diagnose_if' is a clang extension">,
+                            InGroup<GccCompat>;
 
 // SEH
 def err_seh_expected_handler : Error<