[BPF] report Invalid usage of the XADD return value" elegantly (#92742)

Previously `report_fatal_error` is used for reporting something goes
wrong in the backend, but this is confusing because `report_fatal_error`
basically means there are something unexpected & crashed in the backend.

So, turn this "crash" into an elegant error reporting. After this patch,
clang can diagnose it:

    bpf-crash.c:4:30: error: Invalid usage of the XADD return value
4 | u32 next_event_id() { return __sync_fetch_and_add(&GLOBAL_EVENT_ID,
1); }
        |                              ^
    1 error generated.

Author: inclyc

llvm/lib/Target/BPF/BPFMIChecking.cpp

@@ -20,6 +20,7 @@
 #include "llvm/CodeGen/MachineFunctionPass.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/IR/DiagnosticInfo.h"
 #include "llvm/Support/Debug.h"
 
 using namespace llvm;
@@ -164,11 +165,9 @@ bool BPFMIPreEmitChecking::processAtomicInsts() {
       if (hasLiveDefs(MI, TRI)) {
         DebugLoc Empty;
         const DebugLoc &DL = MI.getDebugLoc();
-        if (DL != Empty)
-          report_fatal_error(Twine("line ") + std::to_string(DL.getLine()) +
-                             ": Invalid usage of the XADD return value", false);
-        else
-          report_fatal_error("Invalid usage of the XADD return value", false);
+        const Function &F = MF->getFunction();
+        F.getContext().diagnose(DiagnosticInfoUnsupported{
+            F, "Invalid usage of the XADD return value", DL});
       }
     }
   }

llvm/test/CodeGen/BPF/xadd.ll

@@ -22,7 +22,7 @@ entry:
   call void @llvm.dbg.value(metadata ptr %ptr, metadata !13, metadata !DIExpression()), !dbg !15
   %0 = atomicrmw add ptr %ptr, i32 4 seq_cst, !dbg !16
   %1 = atomicrmw add ptr %ptr, i32 6 seq_cst, !dbg !17
-; CHECK: line 4: Invalid usage of the XADD return value
+; CHECK: in function test i32 (ptr): Invalid usage of the XADD return value
   call void @llvm.dbg.value(metadata i32 %1, metadata !14, metadata !DIExpression()), !dbg !18
   ret i32 %1, !dbg !19
 }