[PATCH] D48412: [RISCV] Add support for interrupt attribute

[Aaron Ballman via Phabricator via cfe-commits]

aaron.ballman added inline comments.


================
Comment at: lib/Sema/SemaDeclAttr.cpp:5305
+
+  if (hasFunctionProto(D) && getFunctionOrMethodNumParams(D) != 0) {
+    S.Diag(D->getLocation(), diag::warn_riscv_interrupt_attribute) << 0;
----------------
apazos wrote:
> aaron.ballman wrote:
> > I would have assumed this would be: `!hasFunctionProto(D) || getFunctionOrMethodNumParams(D) != 0`, but it depends on whether you want to support K&R C functions.
> hasFunctionProto also returns true for a function definition like this one 
>  __attribute__((interrupt)) void foo1(int) {}.
That's correct, which is why I recommended the predicate the way I did. If the function has no prototype, we want to diagnose it. If the function has a prototype, we want to see how many parameters are listed and if there are more than zero parameters, we want to diagnose it.


================
Comment at: test/Sema/riscv-interrupt-attr.c:23
+                                                      // expected-note {{repeated RISC-V 'interrupt' attribute is here}}
+__attribute__((interrupt("user"))) void foo8() {}
+__attribute__((interrupt("supervisor"))) void foo9() {}
----------------
apazos wrote:
> aaron.ballman wrote:
> > aaron.ballman wrote:
> > > Do you intend for functions without a prototype to be accepted? foo8() can be passed an arbitrary number of arguments, which is a bit different than what I thought you wanted the semantic check to be.
> > This question remains outstanding.
> The checks are validating both function definitions and function prototypes like these:
> _attribute__((interrupt)) void foo1() {} 
> __attribute__((interrupt)) void foo(void);
> Not sure what the confusion is.
Ah, now I see where the confusion is.

In C, an empty parameter list declares a function without a prototype; functions without prototypes can accept any number of arguments. To declare a function that accepts no arguments, you must have a prototype for the function and the parameter list is void. In C++, all functions are prototyped and an empty parameter list is equivalent to a parameter list of void. The word "prototype" doesn't mean "forward declaration". e.g.,
```
// C code
void foo1(); // Declaration; no prototype; accepts any number of arguments.
void foo2() {} // Definition; no prototype; accepts any number of arguments.
void foo3(void); // Declaration; prototype; accepts no arguments.
void foo4(void) {} // Definition; prototype; accepts no arguments.

foo2(1, 2, 3); // ok
foo4(1, 2, 3); // error
```
Because a function without a prototype can accept any number of arguments, I think you want to diagnose such a function signature.


https://reviews.llvm.org/D48412