add initial support for __cxa_rethrow

clang/lib/CIR/CodeGen/CIRGenItaniumCXXABI.cpp

@@ -2238,7 +2238,30 @@ mlir::Value CIRGenItaniumCXXABI::getCXXDestructorImplicitParam(
 
 void CIRGenItaniumCXXABI::emitRethrow(CIRGenFunction &CGF, bool isNoReturn) {
   // void __cxa_rethrow();
-  llvm_unreachable("NYI");
+
+  cir::FuncType FTy =
+      CGF.getBuilder().getFuncType({}, CGF.getBuilder().getVoidTy());
+
+  auto Fn = CGF.CGM.createRuntimeFunction(FTy, "__cxa_rethrow");
+
+  if (isNoReturn) {
+    auto &builder = CGF.getBuilder();
+
+    auto callOp = builder.createTryCallOp(Fn.getLoc(), Fn, {});
+
+    // The idea here is to create
+    // an unreachable continue block for the rethrow, but
+    // there is a YieldOp that terminates the TryOp already, so creating an
+    // UnreachableOp in-place causes us to have two terminators which isn't
+    // valid CIR. So, to make this valid CIR the UnreachableOp is created in a
+    // separate scope.
+    builder.create<cir::ScopeOp>(Fn.getLoc(), /*scopeBuilder=*/
+                                 [&](mlir::OpBuilder &b, mlir::Location loc) {
+                                   b.create<cir::UnreachableOp>(loc);
+                                 });
+  } else {
+    llvm_unreachable("NYI");
+  }
 }
 
 void CIRGenItaniumCXXABI::emitThrow(CIRGenFunction &CGF,

clang/test/CIR/CodeGen/try-catch-dtors.cpp

@@ -339,3 +339,40 @@ void bar() {
 // CIR:  cir.store %[[V3]], %[[V1]] : !s32i, !cir.ptr<!s32i>
 // CIR:  cir.call @_ZN1AD2Ev(%[[V0]]) : (!cir.ptr<!ty_A>) -> () extra(#fn_attr)
 // CIR:  cir.return
+
+struct S {
+  S() {}
+};
+
+void refoo() {
+  int r = 1;
+  try {
+    S s;
+    throw;
+  } catch (...) {
+    ++r;
+  }
+}
+
+// CIR-LABEL: @_Z5refoov()
+// CIR: %[[V0:.*]] = cir.alloca !s32i, !cir.ptr<!s32i>, ["r", init] {alignment = 4 : i64}
+// CIR: %[[V1:.*]] = cir.const #cir.int<1> : !s32i
+// CIR: cir.store %[[V1]], %[[V0]] : !s32i, !cir.ptr<!s32i>
+// CIR: cir.scope {
+// CIR: %[[V2:.*]] = cir.alloca !ty_S, !cir.ptr<!ty_S>, ["s", init] {alignment = 1 : i64}
+// CIR: cir.try {
+// CIR:    cir.call exception @_ZN1SC2Ev(%[[V2]]) : (!cir.ptr<!ty_S>) -> ()
+// CIR:    cir.call exception @__cxa_rethrow() : () -> ()
+// CIR:    cir.scope {
+// CIR:      cir.unreachable
+// CIR:    }
+// CIR:    cir.yield
+// CIR:  } catch [type #cir.all {
+// CIR:    %[[V3:.*]] = cir.catch_param -> !cir.ptr<!void>
+// CIR:    %[[V4:.*]] = cir.load %[[V0]] : !cir.ptr<!s32i>, !s32i
+// CIR:    %[[V5:.*]] = cir.unary(inc, %[[V4]]) : !s32i, !s32i
+// CIR:    cir.store %[[V5]], %[[V0]] : !s32i, !cir.ptr<!s32i>
+// CIR:    cir.yield
+// CIR:  }]
+// CIR: }
+// CIR: cir.return