[clang] af99236 - Don't diagnose unused but set when the Cleanup attribute is used.

[Michael Benfield via cfe-commits]

Author: Michael Benfield
Date: 2021-09-22T17:48:09Z
New Revision: af99236747872af7e77092cbf6ddd18fa8623a2f

URL: https://github.com/llvm/llvm-project/commit/af99236747872af7e77092cbf6ddd18fa8623a2f
DIFF: https://github.com/llvm/llvm-project/commit/af99236747872af7e77092cbf6ddd18fa8623a2f.diff

LOG: Don't diagnose unused but set when the Cleanup attribute is used.

This applies to -Wunused-but-set-variable and
-Wunused-but-set-parameter.

This addresses bug 51865.

Differential Revision: https://reviews.llvm.org/D109862

Added: 
    

Modified: 
    clang/lib/Sema/SemaDecl.cpp
    clang/test/Sema/warn-unused-but-set-variables.c

Removed: 
    


################################################################################
diff  --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index cc3417d4ccba..13389ebdd72f 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -1921,8 +1921,10 @@ void Sema::DiagnoseUnusedDecl(const NamedDecl *D) {
 }
 
 void Sema::DiagnoseUnusedButSetDecl(const VarDecl *VD) {
-  // If it's not referenced, it can't be set.
-  if (!VD->isReferenced() || !VD->getDeclName() || VD->hasAttr<UnusedAttr>())
+  // If it's not referenced, it can't be set. If it has the Cleanup attribute,
+  // it's not really unused.
+  if (!VD->isReferenced() || !VD->getDeclName() || VD->hasAttr<UnusedAttr>() ||
+      VD->hasAttr<CleanupAttr>())
     return;
 
   const auto *Ty = VD->getType().getTypePtr()->getBaseElementTypeUnsafe();

diff  --git a/clang/test/Sema/warn-unused-but-set-variables.c b/clang/test/Sema/warn-unused-but-set-variables.c
index a8d05243321f..38042ba014c4 100644
--- a/clang/test/Sema/warn-unused-but-set-variables.c
+++ b/clang/test/Sema/warn-unused-but-set-variables.c
@@ -49,3 +49,13 @@ void f2 (void) {
   x = 0;
   (void) sizeof(x);
 }
+
+void for_cleanup(int *x) {
+  *x = 0;
+}
+
+void f3(void) {
+  // Don't warn if the __cleanup__ attribute is used.
+  __attribute__((__cleanup__(for_cleanup))) int x;
+  x = 5;
+}