[clang] [llvm] [Sanitizer] Make sanitizer passes idempotent (PR #99439)

[Vitaly Buka via llvm-commits]

================
@@ -12,12 +12,47 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Transforms/Instrumentation.h"
+#include "llvm/IR/DiagnosticInfo.h"
+#include "llvm/IR/DiagnosticPrinter.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Module.h"
 #include "llvm/TargetParser/Triple.h"
 
 using namespace llvm;
 
+static cl::opt<bool> ClIgnoreRedundantInstrumentation(
+    "ignore-redundant-instrumentation",
+    cl::desc("Ignore redundant instrumentation"), cl::Hidden, cl::init(false));
+
+namespace {
+/// Diagnostic information for IR instrumentation reporting.
+class DiagnosticInfoInstrumentation : public DiagnosticInfo {
+  const Twine &Msg;
+
+public:
+  DiagnosticInfoInstrumentation(const Twine &DiagMsg,
+                                DiagnosticSeverity Severity = DS_Warning)
+      : DiagnosticInfo(DK_Linker, Severity), Msg(DiagMsg) {}
+  void print(DiagnosticPrinter &DP) const override { DP << Msg; }
+};
+} // namespace
+
+/// Check if module has flag attached, if not add the flag.
+bool llvm::checkIfAlreadyInstrumented(Module &M, StringRef Flag) {
----------------
vitalybuka wrote:

Early return please and DS_Error?



```suggestion
bool llvm::checkIfAlreadyInstrumented(Module &M, StringRef Flag) {
  if (!M.getModuleFlag(Flag)) {
    M.addModuleFlag(Module::ModFlagBehavior::Override, Flag, 1);
    return false;
  }
  if (ClIgnoreRedundantInstrumentation)
    return true;
  std::string diagInfo =
      "Redundant instrumentation detected, with module flag: " +
      std::string(Flag);
  M.getContext().diagnose(DiagnosticInfoInstrumentation(
      diagInfo, DiagnosticSeverity::DS_Error));
  return true;
}
```

https://github.com/llvm/llvm-project/pull/99439