[analyzer] DeadStores: Add a crude suppression files generated by DriverKit IIG.

[NoQ]

Summary

IIG is a replacement for MIG in DriverKit: IIG is autogenerating C++ code. Suppress dead store warnings on such code, as the tool seems to be producing them regularly, and the users of IIG are not in position to address these warnings, as they don't control the autogenerated code. IIG-generated code is identified by looking at the comments at the top of the file.

clang/lib/StaticAnalyzer/Checkers/DeadStoresChecker.cpp

bool isLive(const LiveVariables::LivenessValues &Live, const VarDecl *D) {
     }
     // Treat all VarDecls that occur in EH code as being "always live"
     // when considering to suppress dead stores.  Frequently stores
     // are followed by reads in EH code, but we don't have the ability
     // to analyze that yet.
     return InEH->count(D);
   }
 
+  bool isSuppressed(SourceRange R) {
+    SourceManager &SMgr = Ctx.getSourceManager();
+    SourceLocation Loc = R.getBegin();
+    if (!Loc.isValid())
+      return false;
+
+    FileID FID = SMgr.getFileID(Loc);
+    bool Invalid = false;
+    StringRef Data = SMgr.getBufferData(FID, &Invalid);
+    if (Invalid)
+      return false;
+
+    // Files autogenerated by DriverKit IIG contain some dead stores that
+    // we don't want to report.
+    if (Data.startswith("/* iig generated from"))
+      return true;
+
+    return false;
+  }
+
   void Report(const VarDecl *V, DeadStoreKind dsk,
               PathDiagnosticLocation L, SourceRange R) {
     if (Escaped.count(V))
       return;
 
     // Compute reachable blocks within the CFG for trivial cases
     // where a bogus dead store can be reported because itself is unreachable.
     if (!reachableCode.get()) {
       reachableCode.reset(new ReachableCode(cfg));
       reachableCode->computeReachableBlocks();
     }
 
     if (!reachableCode->isReachable(currentBlock))
       return;
 
+    if (isSuppressed(R))
+      return;
+
     SmallString<64> buf;
     llvm::raw_svector_ostream os(buf);
     const char *BugType = nullptr;
 
     switch (dsk) {
       case DeadInit:
         BugType = "Dead initialization";
         os << "Value stored to '" << *V

clang/test/Analysis/deadstores-driverkit.cpp

+/* iig generated from SomethingSomething.iig */
+
+// The comment above is the whole point of the test.
+// That's how the suppression works.
+// It needs to be on the top.
+// Run-lines can wait.
+
+// RUN: %clang_analyze_cc1 -w -triple x86_64-apple-driverkit19.0 \
+// RUN:   -analyzer-checker=deadcode -verify %s
+
+// expected-no-diagnostics
+
+#include "os_object_base.h"
+
+class OSSomething {
+  kern_return_t Invoke(const IORPC);
+  void foo(OSDispatchMethod supermethod) {
+    kern_return_t ret;
+    IORPC rpc;
+    // Test the DriverKit specific suppression in the dead stores checker.
+    if (supermethod) ret = supermethod((OSObject *)this, rpc); // no-warning
+    else             ret = ((OSObject *)this)->Invoke(rpc); // no-warning
+  }
+};

clang/test/Analysis/os_object_base.h

#define OSDynamicCast(type, inst)   \
     ((type *) OSMetaClassBase::safeMetaCast((inst), OSTypeID(type)))
 #define OSRequiredCast(type, inst)   \
     ((type *) OSMetaClassBase::requiredMetaCast((inst), OSTypeID(type)))
 
 #define OSTypeAlloc(type)   ((type *) ((type::metaClass)->alloc()))
 
 using size_t = decltype(sizeof(int));
 
+typedef int kern_return_t;
+struct IORPC {};
+
 struct OSMetaClass;
 
 struct OSMetaClassBase {
   static OSMetaClassBase *safeMetaCast(const OSMetaClassBase *inst,
                                        const OSMetaClass *meta);
   static OSMetaClassBase *requiredMetaCast(const OSMetaClassBase *inst,
                                            const OSMetaClass *meta);
 
   OSMetaClassBase *metaCast(const char *toMeta);
 
   virtual void retain() const;
   virtual void release() const;
 
   virtual void taggedRetain(const void * tag = nullptr) const;
   virtual void taggedRelease(const void * tag = nullptr) const;
 
   virtual void free();
   virtual ~OSMetaClassBase(){};
+
+  kern_return_t Invoke(IORPC invoke);
 };
 
+typedef kern_return_t (*OSDispatchMethod)(OSMetaClassBase *self,
+                                          const IORPC rpc);
+
 struct OSObject : public OSMetaClassBase {
   virtual ~OSObject(){}
 
   unsigned int foo() { return 42; }
 
   virtual OS_RETURNS_NOT_RETAINED OSObject *identity();
 
   static OSObject *generateObject(int);