[clang][ARM] Emit an error when an interrupt handler is called.

Closes #95359.

Author: chrisnc

clang/docs/ReleaseNotes.rst

@@ -578,7 +578,7 @@ Improvements to Clang's diagnostics
   functions that are called from interrupt handlers to prevent clobbering VFP registers
   as part of ``-Wextra`` (#GH34876). Following this suggestion leads to unpredictable
   behavior. Instead, a new warning, ``-Warm-interrupt-vfp-clobber`` will trigger for
-  interrupt handlers with VFP enabled.
+  interrupt handlers with VFP enabled. Calling an interrupt handler is now an error.
 
 Improvements to Clang's time-trace
 ----------------------------------

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -340,6 +340,8 @@ def warn_arm_interrupt_vfp_clobber : Warning<
   "interrupt service routine with vfp enabled may clobber the "
   "interruptee's vfp state">,
   InGroup<DiagGroup<"arm-interrupt-vfp-clobber">>;
+def err_arm_interrupt_called : Error<
+  "interrupt service routine cannot be called directly">;
 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">,

clang/lib/Sema/SemaExpr.cpp

@@ -6755,9 +6755,15 @@ ExprResult Sema::BuildResolvedCallExpr(Expr *Fn, NamedDecl *NDecl,
   unsigned BuiltinID = (FDecl ? FDecl->getBuiltinID() : 0);
 
   // Functions with 'interrupt' attribute cannot be called directly.
-  if (FDecl && FDecl->hasAttr<AnyX86InterruptAttr>()) {
-    Diag(Fn->getExprLoc(), diag::err_anyx86_interrupt_called);
-    return ExprError();
+  if (FDecl) {
+    if (FDecl->hasAttr<AnyX86InterruptAttr>()) {
+      Diag(Fn->getExprLoc(), diag::err_anyx86_interrupt_called);
+      return ExprError();
+    }
+    if (FDecl->hasAttr<ARMInterruptAttr>()) {
+      Diag(Fn->getExprLoc(), diag::err_arm_interrupt_called);
+      return ExprError();
+    }
   }
 
   // X86 interrupt handlers may only call routines with attribute