[analyzer] Suppress bugs whose paths go through the return of a null pointer.

This is a heuristic intended to greatly reduce the number of false
positives resulting from inlining, particularly inlining of generic,
defensive C++ methods that live in header files. The suppression is
triggered in the cases where we ask to track where a null pointer came
from, and it turns out that the source of the null pointer was an inlined
function call.

This change brings the number of bug reports in LLVM from ~1500 down to
around ~300, a much more manageable number. Yes, some true positives may
be hidden as well, but from what I looked at the vast majority of silenced
reports are false positives, and many of the true issues found by the
analyzer are still reported.

I'm hoping to improve this heuristic further by adding some exceptions
next week (cases in which a bug should still be reported).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@164449 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 8 insertions, 0 deletions

diff --git a/lib/StaticAnalyzer/Core/AnalyzerOptions.cpp b/lib/StaticAnalyzer/Core/AnalyzerOptions.cpp
index 04eb0ad97b..1ffd105766 100644
--- a/lib/StaticAnalyzer/Core/AnalyzerOptions.cpp
+++ b/lib/StaticAnalyzer/Core/AnalyzerOptions.cpp
@@ -90,6 +90,14 @@ bool AnalyzerOptions::mayInlineObjCMethod() const {
   return *ObjCInliningMode;
 }
 
+bool AnalyzerOptions::shouldPruneNullReturnPaths() const {
+  if (!PruneNullReturnPaths.hasValue())
+    const_cast<llvm::Optional<bool> &>(PruneNullReturnPaths) =
+      getBooleanOption("suppress-null-return-paths", /*Default=*/true);
+
+  return *PruneNullReturnPaths;
+}
+
 int AnalyzerOptions::getOptionAsInteger(StringRef Name, int DefaultVal) const {
   std::string OptStr = Config.lookup(Name);
   if (OptStr.empty())