Author: Michael Wyman Date: 2022-02-24T14:26:05-08:00 New Revision: b682616d1fd1263b303985b9f930c1760033af2c
URL: https://github.com/llvm/llvm-project/commit/b682616d1fd1263b303985b9f930c1760033af2c DIFF: https://github.com/llvm/llvm-project/commit/b682616d1fd1263b303985b9f930c1760033af2c.diff LOG: Clang `unused-but-set-variable` warnings should not apply to `__attribute__((objc_precise_lifetime))` Objective-C pointers The `objc_precise_lifetime` attribute is applied to Objective-C pointers to ensure the optimizer does not prematurely release an object under Automatic Reference Counting (ARC). It is a common enough pattern to assign values to these variables but not reference them otherwise, and annotating them with `__unused` is not really correct as they are being used to ensure an object's lifetime. Differential Revision: https://reviews.llvm.org/D120372 Added: clang/test/SemaObjC/objc-precise-lifetime-unused-variable.m Modified: clang/lib/Sema/SemaDecl.cpp Removed: ################################################################################ diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp index 52d9a23386914..671aeb7e9ea69 100644 --- a/clang/lib/Sema/SemaDecl.cpp +++ b/clang/lib/Sema/SemaDecl.cpp @@ -2016,6 +2016,12 @@ void Sema::DiagnoseUnusedButSetDecl(const VarDecl *VD) { if (VD->hasAttr<BlocksAttr>() && Ty->isObjCObjectPointerType()) return; + // Don't warn about Objective-C pointer variables with precise lifetime + // semantics; they can be used to ensure ARC releases the object at a known + // time, which may mean assignment but no other references. + if (VD->hasAttr<ObjCPreciseLifetimeAttr>() && Ty->isObjCObjectPointerType()) + return; + auto iter = RefsMinusAssignments.find(VD); if (iter == RefsMinusAssignments.end()) return; diff --git a/clang/test/SemaObjC/objc-precise-lifetime-unused-variable.m b/clang/test/SemaObjC/objc-precise-lifetime-unused-variable.m new file mode 100644 index 0000000000000..2a140a86b0334 --- /dev/null +++ b/clang/test/SemaObjC/objc-precise-lifetime-unused-variable.m @@ -0,0 +1,22 @@ +// RUN: %clang_cc1 -triple x86_64-apple-macos11 -fsyntax-only -fobjc-arc -fblocks -verify -Wunused-but-set-variable -Wno-objc-root-class %s + +id getFoo(void); + +void test() { + // no diagnostics for objects with precise lifetime semantics. + __attribute__((objc_precise_lifetime)) id x; + x = getFoo(); + + id x2; // expected-warning {{variable 'x2' set but not used}} + x2 = getFoo(); + + do { + __attribute__((objc_precise_lifetime)) id y; + y = getFoo(); + + id y2; // expected-warning {{variable 'y2' set but not used}} + y2 = getFoo(); + } while(0); + + x = ((void *)0); +} _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
