[analyzer] Add "Assuming..." diagnostic pieces for unsupported conditions.

In the analyzer's path-sensitive reports, when a report goes through a branch
and the branch condition cannot be decided to be definitely true or false
(based on the previous execution path), an event piece is added that tells the
user that a new assumption is added upon the symbolic value of the branch
condition. For example, "Assuming 'a' is equal to 3".

The text of the assumption is hand-crafted in various manners depending on
the AST expression. If the AST expression is too complex and the text of
the assumption fails to be constructed, the event piece is omitted.
This causes loss of information and misunderstanding of the report.

Do not omit the event piece even if the expression is too complex;
add a piece with a generic text instead.

Differential Revision: https://reviews.llvm.org/D23300

llvm-svn: 283301

1 files changed, 5 insertions, 3 deletions

diff --git a/clang/lib/StaticAnalyzer/Core/BugReporter.cpp b/clang/lib/StaticAnalyzer/Core/BugReporter.cpp
index e04aa395d49..1800eff76bd 100644
--- a/clang/lib/StaticAnalyzer/Core/BugReporter.cpp
+++ b/clang/lib/StaticAnalyzer/Core/BugReporter.cpp
@@ -78,7 +78,9 @@ static PathDiagnosticEventPiece *
 eventsDescribeSameCondition(PathDiagnosticEventPiece *X,
                             PathDiagnosticEventPiece *Y) {
   // Prefer diagnostics that come from ConditionBRVisitor over
-  // those that came from TrackConstraintBRVisitor.
+  // those that came from TrackConstraintBRVisitor,
+  // unless the one from ConditionBRVisitor is
+  // its generic fallback diagnostic.
   const void *tagPreferred = ConditionBRVisitor::getTag();
   const void *tagLesser = TrackConstraintBRVisitor::getTag();
 
@@ -86,10 +88,10 @@ eventsDescribeSameCondition(PathDiagnosticEventPiece *X,
     return nullptr;
 
   if (X->getTag() == tagPreferred && Y->getTag() == tagLesser)
-    return X;
+    return ConditionBRVisitor::isPieceMessageGeneric(X) ? Y : X;
 
   if (Y->getTag() == tagPreferred && X->getTag() == tagLesser)
-    return Y;
+    return ConditionBRVisitor::isPieceMessageGeneric(Y) ? X : Y;
 
   return nullptr;
 }