[PATCH] D82425: [SemaCXX] Fix false positive of -Wuninitialized-const-reference in empty function body.

[Zequan Wu via Phabricator via cfe-commits]

zequanwu created this revision.
zequanwu added reviewers: hans, nick.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.

Some libraries use empty function to ignore unused variable warnings, which gets a new warning from `-Wuninitialized-const-reference`, discussed here https://reviews.llvm.org/D79895#2107604.
This patch should fix that.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D82425

Files:
  clang/lib/Analysis/UninitializedValues.cpp
  clang/test/SemaCXX/warn-uninitialized-const-reference.cpp


Index: clang/test/SemaCXX/warn-uninitialized-const-reference.cpp
===================================================================
--- clang/test/SemaCXX/warn-uninitialized-const-reference.cpp
+++ clang/test/SemaCXX/warn-uninitialized-const-reference.cpp
@@ -9,6 +9,9 @@
   bool operator!=(const A &);
 };
 
+template <class T>
+inline void ignore_template(T const &) {}
+void ignore(const int &i) {}
 A const_ref_use_A(const A &a);
 int const_ref_use(const int &i);
 A const_use_A(const A a);
@@ -33,4 +36,8 @@
   if (a < 42)
     m = 1;
   const_ref_use(m);
+
+  int l;
+  ignore_template(l);
+  ignore(l);
 }
Index: clang/lib/Analysis/UninitializedValues.cpp
===================================================================
--- clang/lib/Analysis/UninitializedValues.cpp
+++ clang/lib/Analysis/UninitializedValues.cpp
@@ -405,6 +405,15 @@
   return QT->isAnyPointerType() && QT->getPointeeType().isConstQualified();
 }
 
+static bool hasTrivialBody(CallExpr *CE) {
+  if (FunctionDecl *fd = CE->getDirectCallee()) {
+    if (FunctionTemplateDecl *ftd = fd->getPrimaryTemplate())
+      return ftd->getTemplatedDecl()->hasTrivialBody();
+    return fd->hasTrivialBody();
+  }
+  return false;
+}
+
 void ClassifyRefs::VisitCallExpr(CallExpr *CE) {
   // Classify arguments to std::move as used.
   if (CE->isCallToStdMove()) {
@@ -423,7 +432,8 @@
        I != E; ++I) {
     if ((*I)->isGLValue()) {
       if ((*I)->getType().isConstQualified())
-        classify((*I), ConstRefUse);
+        if (!hasTrivialBody(CE))
+          classify((*I), ConstRefUse);
     } else if (isPointerToConst((*I)->getType())) {
       const Expr *Ex = stripCasts(DC->getParentASTContext(), *I);
       const auto *UO = dyn_cast<UnaryOperator>(Ex);


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