[CHERI][Coroutines] Disable LangOpts.Coroutines for purecap

Attempting to generate code for C++20 coroutines is not yet possible
since the underlying LLVM intrinsics are not overloaded.

See #717

clang/lib/Basic/TargetInfo.cpp

@@ -391,6 +391,12 @@ void TargetInfo::adjust(DiagnosticsEngine &Diags, LangOptions &Opts) {
     LongDoubleAlign = 64;
   }
 
+  if (areAllPointersCapabilities()) {
+    // C++20 coroutines are not yet supported for purecap:
+    // https://github.com/CTSRD-CHERI/llvm-project/issues/717
+    Opts.Coroutines = false;
+  }
+
   if (Opts.OpenCL) {
     // OpenCL C requires specific widths for types, irrespective of
     // what these normally are for the target.

clang/lib/Frontend/InitPreprocessor.cpp

@@ -682,7 +682,8 @@ static void InitializeCPlusPlusFeatureTestMacros(const LangOptions &LangOpts,
     //Builder.defineMacro("__cpp_consteval", "201811L");
     Builder.defineMacro("__cpp_constexpr_dynamic_alloc", "201907L");
     Builder.defineMacro("__cpp_constinit", "201907L");
-    Builder.defineMacro("__cpp_impl_coroutine", "201902L");
+    if (LangOpts.Coroutines)
+      Builder.defineMacro("__cpp_impl_coroutine", "201902L");
     Builder.defineMacro("__cpp_designated_initializers", "201707L");
     Builder.defineMacro("__cpp_impl_three_way_comparison", "201907L");
     //Builder.defineMacro("__cpp_modules", "201907L");

clang/test/Preprocessor/cheri-coroutines.cpp

@@ -0,0 +1,32 @@
+/// Coroutines are not yet supported for purecap, make sure we emit an error
+/// instead crashing while trying to generate code.
+/// See https://github.com/CTSRD-CHERI/llvm-project/issues/717
+
+// RUN: %riscv64_cheri_cc1 -std=c++17 -fcoroutines-ts -E -dM -x c++ /dev/null \
+// RUN:    | FileCheck %s --check-prefixes=HYBRID-CXX17-TS
+// HYBRID-CXX17-TS: #define __cplusplus 201703L
+// HYBRID-CXX17-TS: #define __cpp_coroutines 201703L
+// RUN: %riscv64_cheri_purecap_cc1 -std=c++17 -fcoroutines-ts -E -dM -x c++ /dev/null \
+// RUN:    | FileCheck %s --check-prefix=PURECAP-CXX17-TS
+// PURECAP-CXX17-TS: #define __cplusplus 201703L
+// PURECAP-CXX17-TS-NOT: #define __cpp_coroutines
+// PURECAP-CXX17-TS-NOT: #define __cpp_impl_coroutine
+
+// RUN: %riscv64_cheri_cc1 -std=c++17 -E -dM -x c++ /dev/null \
+// RUN:    | FileCheck %s --check-prefix=CXX17-NO-TS
+// RUN: %riscv64_cheri_purecap_cc1 -std=c++17 -E -dM -x c++ /dev/null \
+// RUN:    | FileCheck %s --check-prefix=CXX17-NO-TS
+// CXX17-NO-TS:     #define __cplusplus 201703L
+// CXX17-NO-TS-NOT: #define __cpp_coroutines
+// CXX17-NO-TS-NOT: #define __cpp_impl_coroutine
+
+// RUN: %riscv64_cheri_cc1 -std=c++20 -E -dM -x c++ /dev/null \
+// RUN:    | FileCheck %s --check-prefixes=HYBRID-CXX20
+// HYBRID-CXX20: #define __cplusplus 202002L
+// HYBRID-CXX20: #define __cpp_coroutines 201703L
+// HYBRID-CXX20: #define __cpp_impl_coroutine 201902L
+// RUN: %riscv64_cheri_purecap_cc1 -std=c++20 -E -dM -x c++ /dev/null \
+// RUN:    | FileCheck %s --check-prefix=PURECAP-CXX20
+// PURECAP-CXX20: #define __cplusplus 202002L
+// PURECAP-CXX20-NOT: #define __cpp_coroutines
+// PURECAP-CXX20-NOT: #define __cpp_impl_coroutine