[clang] Modify diagnostic level from err to warn: anyx86_interrupt_regsave

[mibintc]

Summary

I got a bug report that https://reviews.llvm.org/D97764 which introduced this diagnostic, was causing problems in interrupt service routines, complaining about functions like abort, exit, or the x86intrin routines (that are really just inlined asm). I think modifying the diagnostic level from error to warn is the safest way to deal with the problem. Checking "always inline" attribute on the called function isn't itself enough without knowing that the called function is leaf. (Separately, perhaps x86intrin functions should be decorated with attribute 'no_caller_saved_registers' in their declarations.)

[rsmith]

clang/include/clang/Basic/DiagnosticSemaKinds.td

299

Please don't add warnings directly to -Wextra; this should have its own flag so that people who want to do this can turn the warning off without turning off all of -Wextra.

[mibintc]

I removed the diagnostic from InGroup<Extra>, that's the only change from previous revision

[mibintc]

clang/include/clang/Basic/DiagnosticSemaKinds.td

299

Thanks, I had thought about removing InGroup<Extra> before uploading to review but hurrying at the end of my work day and forgot. I was expecting the lit test to fail and I'd have to add Wextra onto the RUN line but I didn't need to do that, the diagnostic was produced without enabling. Anyway I got rid of it like you asked.

BTW the only other diagnostic in this file marked Wextra is the arm diagnostic. That was added in https://reviews.llvm.org/D28820 "warn_arm_interrupt_calling_convention"

[aaron.ballman]

clang/include/clang/Basic/DiagnosticSemaKinds.td

295–299

You still need to add the diagnostic to a diagnostic group, otherwise users don't have a way to selectively disable the diagnostic.

Feel free to pick a different group for the -W flag; I just took a stab at a possible name.

This should fix the failing CI pipelines too.

[mibintc]

I added the InGroup rule for the new warning diagnostic like Aaron requested

[aaron.ballman]

LGTM!

clang/include/clang/Basic/DiagnosticSemaKinds.td

def ext_parameter_name_omitted_c2x : ExtWarn<
   "omitting the parameter name in a function definition is a C2x extension">,
   InGroup<C2x>;
 def err_anyx86_interrupt_attribute : Error<
   "%select{x86|x86-64}0 'interrupt' attribute only applies to functions that "
   "have %select{a 'void' return type|"
   "only a pointer parameter optionally followed by an integer parameter|"
   "a pointer as the first parameter|a %2 type as the second parameter}1">;
 def err_anyx86_interrupt_called : Error<
   "interrupt service routine cannot be called directly">;
-def err_anyx86_interrupt_regsave : Error<
-  "interrupt service routine may only call a function"
-  " with attribute 'no_caller_saved_registers'">;
+def warn_anyx86_interrupt_regsave : Warning<
+  "interrupt service routine should only call a function"
+  " with attribute 'no_caller_saved_registers'">,
+  InGroup<DiagGroup<"interrupt-service-routine">>;
 def warn_arm_interrupt_calling_convention : Warning<
    "call to function without interrupt attribute could clobber interruptee's VFP registers">,
    InGroup<Extra>;
 def warn_interrupt_attribute_invalid : Warning<
    "%select{MIPS|MSP430|RISC-V}0 'interrupt' attribute only applies to "
    "functions that have %select{no parameters|a 'void' return type}1">,
    InGroup<IgnoredAttributes>;
 def warn_riscv_repeated_interrupt_attribute : Warning<

clang/lib/Sema/SemaExpr.cpp

if (Caller->hasAttr<ARMInterruptAttr>()) {
       if (VFP && (!FDecl || !FDecl->hasAttr<ARMInterruptAttr>())) {
         Diag(Fn->getExprLoc(), diag::warn_arm_interrupt_calling_convention);
         if (FDecl)
           Diag(FDecl->getLocation(), diag::note_callee_decl) << FDecl;
       }
     }
     if (Caller->hasAttr<AnyX86InterruptAttr>() &&
         ((!FDecl || !FDecl->hasAttr<AnyX86NoCallerSavedRegistersAttr>()))) {
-      Diag(Fn->getExprLoc(), diag::err_anyx86_interrupt_regsave);
+      Diag(Fn->getExprLoc(), diag::warn_anyx86_interrupt_regsave);
       if (FDecl)
         Diag(FDecl->getLocation(), diag::note_callee_decl) << FDecl;
     }
   }
 
   // Promote the function operand.
   // We special-case function promotion here because we only allow promoting
   // builtin functions to function pointers in the callee of a call.

clang/test/Sema/attr-x86-interrupt.c

 typedef unsigned long long Arg2Type;
 #else
 typedef unsigned int Arg2Type;
 #endif
 #ifndef NOCALLERSAVE
 __attribute__((no_caller_saved_registers))
 #else
 // expected-note@+3 {{'foo9' declared here}}
-// expected-error@+4 {{interrupt service routine may only call a function with attribute 'no_caller_saved_registers'}}
+// expected-warning@+4 {{interrupt service routine should only call a function with attribute 'no_caller_saved_registers'}}
 #endif
 void foo9(int *a, Arg2Type b) {}
 __attribute__((interrupt)) void fooA(int *a, Arg2Type b) {
   foo9(a, b);
 }
 void g(void (*fp)(int *));
 int main(int argc, char **argv) {
   void *ptr = (void *)&foo7;