[clang] [clang] Don't emit the warn_dangling_lifetime_pointer diagnostic for the assignment case. (PR #97408)

Haojian Wu via cfe-commits cfe-commits at lists.llvm.org
Tue Jul 2 06:12:45 PDT 2024


https://github.com/hokein updated https://github.com/llvm/llvm-project/pull/97408

>From d1ea90918702fec85714bdd9caa68942eb4a4218 Mon Sep 17 00:00:00 2001
From: Haojian Wu <hokein.wu at gmail.com>
Date: Tue, 2 Jul 2024 14:12:36 +0200
Subject: [PATCH 1/3] [clang] Don't emit the warn_dangling_lifetime_pointer
 diagnostic for the assignment case.

The lifetime_pointer case is handled before the assignment case. In some
scenario where we have the gsl::Pointer attr, we will end up with
emitting the `-Wdangling-gsl` warning for the assignment case. This
means we can not use `-Wno-dangling-assignment` to suppress the
newly-added warning.
---
 clang/lib/Sema/CheckExprLifetime.cpp              |  2 +-
 .../test/SemaCXX/suppress-dangling-assignment.cpp | 15 +++++++++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)
 create mode 100644 clang/test/SemaCXX/suppress-dangling-assignment.cpp

diff --git a/clang/lib/Sema/CheckExprLifetime.cpp b/clang/lib/Sema/CheckExprLifetime.cpp
index fea0239f7bc36..03bf87a7cf5e6 100644
--- a/clang/lib/Sema/CheckExprLifetime.cpp
+++ b/clang/lib/Sema/CheckExprLifetime.cpp
@@ -1023,7 +1023,7 @@ static void checkExprLifetimeImpl(Sema &SemaRef,
         return false;
       }
 
-      if (IsGslPtrInitWithGslTempOwner && DiagLoc.isValid()) {
+      if (InitEntity && IsGslPtrInitWithGslTempOwner && DiagLoc.isValid()) {
         SemaRef.Diag(DiagLoc, diag::warn_dangling_lifetime_pointer)
             << DiagRange;
         return false;
diff --git a/clang/test/SemaCXX/suppress-dangling-assignment.cpp b/clang/test/SemaCXX/suppress-dangling-assignment.cpp
new file mode 100644
index 0000000000000..11625d3272b83
--- /dev/null
+++ b/clang/test/SemaCXX/suppress-dangling-assignment.cpp
@@ -0,0 +1,15 @@
+
+// RUN: %clang_cc1 -std=c++20 -verify -Wno-dangling-assignment %s
+// expected-no-diagnostics
+
+namespace std {
+// std::basic_string has a hard-coded gsl::owner attr.
+struct basic_string {
+  const char* c_str();
+};
+}  // namespace std
+
+void test(const char* a) {
+  // verify that the dangling-assignment diagnostic are suppressed. 
+  a = std::basic_string().c_str();
+}

>From 95233e150d4344411d41539c57a3e921d621ea0b Mon Sep 17 00:00:00 2001
From: Haojian Wu <hokein.wu at gmail.com>
Date: Tue, 2 Jul 2024 14:35:47 +0200
Subject: [PATCH 2/3] Refine the test, verifing that  we emit the
 "-Wdangling-assignment" warning.

---
 .../test/SemaCXX/suppress-dangling-assignment.cpp | 15 ---------------
 clang/test/SemaCXX/warn-dangling-local.cpp        | 11 +++++++++++
 2 files changed, 11 insertions(+), 15 deletions(-)
 delete mode 100644 clang/test/SemaCXX/suppress-dangling-assignment.cpp

diff --git a/clang/test/SemaCXX/suppress-dangling-assignment.cpp b/clang/test/SemaCXX/suppress-dangling-assignment.cpp
deleted file mode 100644
index 11625d3272b83..0000000000000
--- a/clang/test/SemaCXX/suppress-dangling-assignment.cpp
+++ /dev/null
@@ -1,15 +0,0 @@
-
-// RUN: %clang_cc1 -std=c++20 -verify -Wno-dangling-assignment %s
-// expected-no-diagnostics
-
-namespace std {
-// std::basic_string has a hard-coded gsl::owner attr.
-struct basic_string {
-  const char* c_str();
-};
-}  // namespace std
-
-void test(const char* a) {
-  // verify that the dangling-assignment diagnostic are suppressed. 
-  a = std::basic_string().c_str();
-}
diff --git a/clang/test/SemaCXX/warn-dangling-local.cpp b/clang/test/SemaCXX/warn-dangling-local.cpp
index a946b8a241a38..2808a4c01f88d 100644
--- a/clang/test/SemaCXX/warn-dangling-local.cpp
+++ b/clang/test/SemaCXX/warn-dangling-local.cpp
@@ -26,3 +26,14 @@ void g() {
   const int a[] = {a[0]};
   const int b[] = {a[0]};
 }
+
+namespace std {
+// std::basic_string has a hard-coded gsl::owner attr.
+struct basic_string {
+  const char* c_str();
+};
+}  // namespace std
+void test(const char* a) {
+  // verify we're emitting the `-Wdangling-assignment` warning.
+  a = std::basic_string().c_str(); // expected-warning {{object backing the pointer a will be destroyed at the end of the full-expression}}
+}

>From 9684db804e397e8615d8d1f1c09397f4e0c1ac20 Mon Sep 17 00:00:00 2001
From: Haojian Wu <hokein.wu at gmail.com>
Date: Tue, 2 Jul 2024 15:12:10 +0200
Subject: [PATCH 3/3] address review comment, restructure the code.

---
 clang/lib/Sema/CheckExprLifetime.cpp | 35 ++++++++++++++--------------
 1 file changed, 17 insertions(+), 18 deletions(-)

diff --git a/clang/lib/Sema/CheckExprLifetime.cpp b/clang/lib/Sema/CheckExprLifetime.cpp
index 03bf87a7cf5e6..2f9ef28da2c3e 100644
--- a/clang/lib/Sema/CheckExprLifetime.cpp
+++ b/clang/lib/Sema/CheckExprLifetime.cpp
@@ -1008,7 +1008,19 @@ static void checkExprLifetimeImpl(Sema &SemaRef,
           return true;
       }
     }
+    if (AEntity) {
+      if (!MTE)
+        return false;
+      assert(shouldLifetimeExtendThroughPath(Path) ==
+                 PathLifetimeKind::NoExtend &&
+             "No lifetime extension for assignments");
+      if (!pathContainsInit(Path))
+        SemaRef.Diag(DiagLoc, diag::warn_dangling_pointer_assignment)
+            << AEntity->LHS << DiagRange;
+      return false;
+    }
 
+    assert(InitEntity && "only for initialization");
     switch (LK) {
     case LK_FullExpression:
       llvm_unreachable("already handled this");
@@ -1023,7 +1035,7 @@ static void checkExprLifetimeImpl(Sema &SemaRef,
         return false;
       }
 
-      if (InitEntity && IsGslPtrInitWithGslTempOwner && DiagLoc.isValid()) {
+      if (IsGslPtrInitWithGslTempOwner && DiagLoc.isValid()) {
         SemaRef.Diag(DiagLoc, diag::warn_dangling_lifetime_pointer)
             << DiagRange;
         return false;
@@ -1031,8 +1043,6 @@ static void checkExprLifetimeImpl(Sema &SemaRef,
 
       switch (shouldLifetimeExtendThroughPath(Path)) {
       case PathLifetimeKind::Extend:
-        assert(InitEntity && "Lifetime extension should happen only for "
-                             "initialization and not assignment");
         // Update the storage duration of the materialized temporary.
         // FIXME: Rebuild the expression instead of mutating it.
         MTE->setExtendingDecl(ExtendingEntity->getDecl(),
@@ -1041,8 +1051,6 @@ static void checkExprLifetimeImpl(Sema &SemaRef,
         return true;
 
       case PathLifetimeKind::ShouldExtend:
-        assert(InitEntity && "Lifetime extension should happen only for "
-                             "initialization and not assignment");
         // We're supposed to lifetime-extend the temporary along this path (per
         // the resolution of DR1815), but we don't support that yet.
         //
@@ -1060,23 +1068,16 @@ static void checkExprLifetimeImpl(Sema &SemaRef,
         if (pathContainsInit(Path))
           return false;
 
-        if (InitEntity) {
-          SemaRef.Diag(DiagLoc, diag::warn_dangling_variable)
-              << RK << !InitEntity->getParent()
-              << ExtendingEntity->getDecl()->isImplicit()
-              << ExtendingEntity->getDecl() << Init->isGLValue() << DiagRange;
-        } else {
-          SemaRef.Diag(DiagLoc, diag::warn_dangling_pointer_assignment)
-              << AEntity->LHS << DiagRange;
-        }
+        SemaRef.Diag(DiagLoc, diag::warn_dangling_variable)
+            << RK << !InitEntity->getParent()
+            << ExtendingEntity->getDecl()->isImplicit()
+            << ExtendingEntity->getDecl() << Init->isGLValue() << DiagRange;
         break;
       }
       break;
     }
 
     case LK_MemInitializer: {
-      assert(InitEntity && "Expect only on initializing the entity");
-
       if (MTE) {
         // Under C++ DR1696, if a mem-initializer (or a default member
         // initializer used by the absence of one) would lifetime-extend a
@@ -1151,7 +1152,6 @@ static void checkExprLifetimeImpl(Sema &SemaRef,
     }
 
     case LK_New:
-      assert(InitEntity && "Expect only on initializing the entity");
       if (isa<MaterializeTemporaryExpr>(L)) {
         if (IsGslPtrInitWithGslTempOwner)
           SemaRef.Diag(DiagLoc, diag::warn_dangling_lifetime_pointer)
@@ -1169,7 +1169,6 @@ static void checkExprLifetimeImpl(Sema &SemaRef,
 
     case LK_Return:
     case LK_StmtExprResult:
-      assert(InitEntity && "Expect only on initializing the entity");
       if (auto *DRE = dyn_cast<DeclRefExpr>(L)) {
         // We can't determine if the local variable outlives the statement
         // expression.



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