[Sema] Patch to issue warning on comparing parameters with

nonnull attribute when comparison is always true/false. 
Original patch by Steven Wu. I have added extra code to prevent issuing of
warning  when the nonnull parameter is modified prior to the comparison.
This addition prevents false positives in the most obvious cases.
There may still be false positive warnings in some cases (as one of my tests
indicates), but benefit far outweighs such cases. rdar://18712242

llvm-svn: 222264

1 files changed, 20 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 1429df778b5..0104020bba8 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -9121,6 +9121,24 @@ QualType Sema::CheckAddressOfOperand(ExprResult &OrigOp, SourceLocation OpLoc) {
   return Context.getPointerType(op->getType());
 }
 
+static void RecordModifiableNonNullParam(Sema &S, const Expr *Exp) {
+  const DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(Exp);
+  if (!DRE)
+    return;
+  const Decl *D = DRE->getDecl();
+  if (!D)
+    return;
+  const ParmVarDecl *Param = dyn_cast<ParmVarDecl>(D);
+  if (!Param)
+    return;
+  if (const FunctionDecl* FD = dyn_cast<FunctionDecl>(Param->getDeclContext()))
+    if (!FD->hasAttr<NonNullAttr>())
+      return;
+  if (FunctionScopeInfo *FD = S.getCurFunction())
+    if (!FD->ModifiedNonNullParams.count(Param))
+      FD->ModifiedNonNullParams.insert(Param);
+}
+
 /// CheckIndirectionOperand - Type check unary indirection (prefix '*').
 static QualType CheckIndirectionOperand(Sema &S, Expr *Op, ExprValueKind &VK,
                                         SourceLocation OpLoc) {
@@ -9360,6 +9378,7 @@ ExprResult Sema::CreateBuiltinBinOp(SourceLocation OpLoc,
     }
     if (!ResultTy.isNull())
       DiagnoseSelfAssignment(*this, LHS.get(), RHS.get(), OpLoc);
+    RecordModifiableNonNullParam(*this, LHS.get());
     break;
   case BO_PtrMemD:
   case BO_PtrMemI:
@@ -9833,6 +9852,7 @@ ExprResult Sema::CreateBuiltinUnaryOp(SourceLocation OpLoc,
     break;
   case UO_AddrOf:
     resultType = CheckAddressOfOperand(Input, OpLoc);
+    RecordModifiableNonNullParam(*this, InputExpr);
     break;
   case UO_Deref: {
     Input = DefaultFunctionArrayLvalueConversion(Input.get());