[clang] [clang][Sema] Warn on self move for inlined static cast (PR #76646)

Max Winkler via cfe-commits cfe-commits at lists.llvm.org
Tue Mar 5 17:23:07 PST 2024


https://github.com/MaxEW707 updated https://github.com/llvm/llvm-project/pull/76646

>From a081f8266f24405523e6d283318bd898fd2d376a Mon Sep 17 00:00:00 2001
From: MaxEW707 <82551778+MaxEW707 at users.noreply.github.com>
Date: Sat, 30 Dec 2023 22:00:38 -0500
Subject: [PATCH 1/4] Warn on self move for inlined static cast

---
 clang/lib/Sema/SemaChecking.cpp       | 19 ++++++++++++++-----
 clang/test/SemaCXX/warn-self-move.cpp | 13 +++++++++++++
 2 files changed, 27 insertions(+), 5 deletions(-)

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index 2a69325f029514..a21410434d8099 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -18843,17 +18843,26 @@ void Sema::DiagnoseSelfMove(const Expr *LHSExpr, const Expr *RHSExpr,
   LHSExpr = LHSExpr->IgnoreParenImpCasts();
   RHSExpr = RHSExpr->IgnoreParenImpCasts();
 
-  // Check for a call expression
+  // Check for a call expression or static_cast expression
   const CallExpr *CE = dyn_cast<CallExpr>(RHSExpr);
-  if (!CE || CE->getNumArgs() != 1)
+  const CXXStaticCastExpr *CXXSCE = dyn_cast<CXXStaticCastExpr>(RHSExpr);
+  if (!CE && !CXXSCE)
     return;
 
   // Check for a call to std::move
-  if (!CE->isCallToStdMove())
+  if (CE && (CE->getNumArgs() != 1 || !CE->isCallToStdMove()))
     return;
 
-  // Get argument from std::move
-  RHSExpr = CE->getArg(0);
+  // Check for a static_cast<T&&>(..) to an xvalue which we can treat as an
+  // inlined std::move
+  if (CXXSCE && !CXXSCE->isXValue())
+    return;
+
+  // Get argument from std::move or static_cast
+  if (CE)
+    RHSExpr = CE->getArg(0);
+  else
+    RHSExpr = CXXSCE->getSubExpr();
 
   const DeclRefExpr *LHSDeclRef = dyn_cast<DeclRefExpr>(LHSExpr);
   const DeclRefExpr *RHSDeclRef = dyn_cast<DeclRefExpr>(RHSExpr);
diff --git a/clang/test/SemaCXX/warn-self-move.cpp b/clang/test/SemaCXX/warn-self-move.cpp
index 0987e9b6bf6017..d0158626424142 100644
--- a/clang/test/SemaCXX/warn-self-move.cpp
+++ b/clang/test/SemaCXX/warn-self-move.cpp
@@ -16,6 +16,9 @@ void int_test() {
   x = std::move(x);  // expected-warning{{explicitly moving}}
   (x) = std::move(x);  // expected-warning{{explicitly moving}}
 
+  x = static_cast<int&&>(x);  // expected-warning{{explicitly moving}}
+  (x) = static_cast<int&&>(x);  // expected-warning{{explicitly moving}}
+
   using std::move;
   x = move(x); // expected-warning{{explicitly moving}} \
                    expected-warning {{unqualified call to 'std::move}}
@@ -26,6 +29,9 @@ void global_int_test() {
   global = std::move(global);  // expected-warning{{explicitly moving}}
   (global) = std::move(global);  // expected-warning{{explicitly moving}}
 
+  global = static_cast<int&&>(global);  // expected-warning{{explicitly moving}}
+  (global) = static_cast<int&&>(global);  // expected-warning{{explicitly moving}}
+
   using std::move;
   global = move(global); // expected-warning{{explicitly moving}} \
                              expected-warning {{unqualified call to 'std::move}}
@@ -35,11 +41,14 @@ class field_test {
   int x;
   field_test(field_test&& other) {
     x = std::move(x);  // expected-warning{{explicitly moving}}
+    x = static_cast<int&&>(x);  // expected-warning{{explicitly moving}}
     x = std::move(other.x);
     other.x = std::move(x);
     other.x = std::move(other.x);  // expected-warning{{explicitly moving}}
+    other.x = static_cast<int&&>(other.x);  // expected-warning{{explicitly moving}}
   }
   void withSuggest(int x) {
+    x = static_cast<int&&>(x); // expected-warning{{explicitly moving variable of type 'int' to itself; did you mean to move to member 'x'?}}
     x = std::move(x); // expected-warning{{explicitly moving variable of type 'int' to itself; did you mean to move to member 'x'?}}
   }
 };
@@ -50,11 +59,15 @@ struct C { C() {}; ~C() {} };
 void struct_test() {
   A a;
   a = std::move(a);  // expected-warning{{explicitly moving}}
+  a = static_cast<A&&>(a);  // expected-warning{{explicitly moving}}
 
   B b;
   b = std::move(b);  // expected-warning{{explicitly moving}}
+  b = static_cast<B&&>(b);  // expected-warning{{explicitly moving}}
   b.a = std::move(b.a);  // expected-warning{{explicitly moving}}
+  b.a = static_cast<A&&>(b.a);  // expected-warning{{explicitly moving}}
 
   C c;
   c = std::move(c);  // expected-warning{{explicitly moving}}
+  c = static_cast<C&&>(c);  // expected-warning{{explicitly moving}}
 }

>From ecd9d5bf0d3fa0bc3e64266c6e7586da25438652 Mon Sep 17 00:00:00 2001
From: MaxEW707 <82551778+MaxEW707 at users.noreply.github.com>
Date: Sun, 31 Dec 2023 17:47:03 -0500
Subject: [PATCH 2/4] use auto

---
 clang/lib/Sema/SemaChecking.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index a21410434d8099..ecb3269d0d30c7 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -18845,7 +18845,7 @@ void Sema::DiagnoseSelfMove(const Expr *LHSExpr, const Expr *RHSExpr,
 
   // Check for a call expression or static_cast expression
   const CallExpr *CE = dyn_cast<CallExpr>(RHSExpr);
-  const CXXStaticCastExpr *CXXSCE = dyn_cast<CXXStaticCastExpr>(RHSExpr);
+  const auto *CXXSCE = dyn_cast<CXXStaticCastExpr>(RHSExpr);
   if (!CE && !CXXSCE)
     return;
 

>From a02d21f4e013efd823a0b078950948b534e31e8e Mon Sep 17 00:00:00 2001
From: MaxEW707 <82551778+MaxEW707 at users.noreply.github.com>
Date: Tue, 5 Mar 2024 19:51:00 -0500
Subject: [PATCH 3/4] PR feedback on reducing logic

---
 clang/lib/Sema/SemaChecking.cpp | 26 ++++++++------------------
 1 file changed, 8 insertions(+), 18 deletions(-)

diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index ecb3269d0d30c7..c3f2650113f6c9 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -18843,26 +18843,16 @@ void Sema::DiagnoseSelfMove(const Expr *LHSExpr, const Expr *RHSExpr,
   LHSExpr = LHSExpr->IgnoreParenImpCasts();
   RHSExpr = RHSExpr->IgnoreParenImpCasts();
 
-  // Check for a call expression or static_cast expression
-  const CallExpr *CE = dyn_cast<CallExpr>(RHSExpr);
-  const auto *CXXSCE = dyn_cast<CXXStaticCastExpr>(RHSExpr);
-  if (!CE && !CXXSCE)
-    return;
-
-  // Check for a call to std::move
-  if (CE && (CE->getNumArgs() != 1 || !CE->isCallToStdMove()))
-    return;
-
-  // Check for a static_cast<T&&>(..) to an xvalue which we can treat as an
-  // inlined std::move
-  if (CXXSCE && !CXXSCE->isXValue())
-    return;
-
-  // Get argument from std::move or static_cast
-  if (CE)
+  // Check for a call to std::move or for a static_cast<T&&>(..) to an xvalue
+  // which we can treat as an inlined std::move
+  if (const auto *CE = dyn_cast<CallExpr>(RHSExpr);
+      CE && CE->getNumArgs() == 1 && CE->isCallToStdMove())
     RHSExpr = CE->getArg(0);
-  else
+  else if (const auto *CXXSCE = dyn_cast<CXXStaticCastExpr>(RHSExpr);
+           CXXSCE && CXXSCE->isXValue())
     RHSExpr = CXXSCE->getSubExpr();
+  else
+    return;
 
   const DeclRefExpr *LHSDeclRef = dyn_cast<DeclRefExpr>(LHSExpr);
   const DeclRefExpr *RHSDeclRef = dyn_cast<DeclRefExpr>(RHSExpr);

>From bfaded8c9ba48e436a9061afcc5c48920cb6c21c Mon Sep 17 00:00:00 2001
From: MaxEW707 <82551778+MaxEW707 at users.noreply.github.com>
Date: Tue, 5 Mar 2024 20:22:52 -0500
Subject: [PATCH 4/4] Add unit tests that shouldn't warn

---
 clang/test/SemaCXX/warn-self-move.cpp | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/clang/test/SemaCXX/warn-self-move.cpp b/clang/test/SemaCXX/warn-self-move.cpp
index d0158626424142..5937bb705ed227 100644
--- a/clang/test/SemaCXX/warn-self-move.cpp
+++ b/clang/test/SemaCXX/warn-self-move.cpp
@@ -43,7 +43,9 @@ class field_test {
     x = std::move(x);  // expected-warning{{explicitly moving}}
     x = static_cast<int&&>(x);  // expected-warning{{explicitly moving}}
     x = std::move(other.x);
+    x = static_cast<int&&>(other.x);
     other.x = std::move(x);
+    other.x = static_cast<int&&>(x);
     other.x = std::move(other.x);  // expected-warning{{explicitly moving}}
     other.x = static_cast<int&&>(other.x);  // expected-warning{{explicitly moving}}
   }



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