feat(compiler)!: add try-catch with C++ stack unwinding

Add TRY/CATCH/ENDTRY and anonymous THROW statements. Use LLVM exception
handling and the C++ ABI to propagate exceptions across function calls,
clean up catch state, and handle uncaught exceptions at the program boundary.
Register exception runtime symbols for the statically linked embedded runner.

Verify runtime checks, nested catches, returns, loops, and invalid syntax
with smoke programs; exercise unwinding with MCJIT, lli, and native binaries.

BREAKING CHANGE: Runtime check failures now throw anonymous exceptions and
print only a generic message when uncaught. Native binaries require linking
the C++ runtime.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

1 files changed, 34 insertions, 0 deletions

diff --git a/tools/driver/EmbeddedRunner.cc b/tools/driver/EmbeddedRunner.cc
index 83489b1..56e3195 100644
--- a/tools/driver/EmbeddedRunner.cc
+++ b/tools/driver/EmbeddedRunner.cc
@@ -7,6 +7,39 @@
 #include "llvm/Support/TargetSelect.h"
 #include "llvm/TargetParser/Host.h"
 #include "llvm/Transforms/Utils/Cloning.h"
+#include <cxxabi.h>
+#include <typeinfo>
+#include <unwind.h>
+
+// Static C++ runtime symbols are not available through dlsym. Register their
+// actual addresses so the JIT and its unwind tables use the host's runtime.
+extern "C" int
+#if defined(__SEH__)
+__gxx_personality_seh0
+#elif defined(__USING_SJLJ_EXCEPTIONS__)
+__gxx_personality_sj0
+#else
+__gxx_personality_v0
+#endif
+(int, _Unwind_Action, _Unwind_Exception_Class, _Unwind_Exception *, _Unwind_Context *);
+
+static void registerExceptionSymbols() {
+    using llvm::sys::DynamicLibrary;
+    DynamicLibrary::AddSymbol("__cxa_allocate_exception", reinterpret_cast<void *>(&__cxxabiv1::__cxa_allocate_exception));
+    DynamicLibrary::AddSymbol("__cxa_throw", reinterpret_cast<void *>(&__cxxabiv1::__cxa_throw));
+    DynamicLibrary::AddSymbol("__cxa_begin_catch", reinterpret_cast<void *>(&__cxxabiv1::__cxa_begin_catch));
+    DynamicLibrary::AddSymbol("__cxa_end_catch", reinterpret_cast<void *>(&__cxxabiv1::__cxa_end_catch));
+    DynamicLibrary::AddSymbol("_ZTIi", const_cast<std::type_info *>(&typeid(int)));
+#if defined(__SEH__)
+    DynamicLibrary::AddSymbol("__gxx_personality_seh0", reinterpret_cast<void *>(&__gxx_personality_seh0));
+#elif defined(__USING_SJLJ_EXCEPTIONS__)
+    DynamicLibrary::AddSymbol("__gxx_personality_sj0", reinterpret_cast<void *>(&__gxx_personality_sj0));
+    DynamicLibrary::AddSymbol("_Unwind_SjLj_Resume", reinterpret_cast<void *>(&_Unwind_SjLj_Resume));
+#else
+    DynamicLibrary::AddSymbol("__gxx_personality_v0", reinterpret_cast<void *>(&__gxx_personality_v0));
+#endif
+    DynamicLibrary::AddSymbol("_Unwind_Resume", reinterpret_cast<void *>(&_Unwind_Resume));
+}
 
 int runEmbedded(const cps::CodeGen &CG) {
     if (llvm::InitializeNativeTarget() || llvm::InitializeNativeTargetAsmPrinter()) {
@@ -18,6 +51,7 @@ int runEmbedded(const cps::CodeGen &CG) {
         llvm::errs() << "error: cannot load process symbols: " << Error << "\n";
         return 1;
     }
+    registerExceptionSymbols();
     // Keep CodeGen's module and context alive while the engine owns its clone.
     auto Module = llvm::CloneModule(CG.getModule());
     Module->setTargetTriple(llvm::sys::getProcessTriple());