sberg created this revision.
sberg added a reviewer: mbenfield.
sberg added a project: clang.
sberg requested review of this revision.
At least LibreOffice has, for mainly historic reasons that would be hard to
change now, a class `Any` with an overloaded `operator >>=` that semantically
does not assign to the LHS but rather extracts into the (by-reference) RHS.
Which thus caused false positive `-Wunused-but-set-parameter` and
`-Wunused-but-set-variable` after those have been introduced recently.
This change is more conservative about the assumed semantics of overloaded
operators, excluding compound assignment operators but keeping plain `operator
=` ones. At least for LibreOffice, that strikes a good balance of not
producing false positives but still finding lots of true ones.
https://reviews.llvm.org/D103949
Files:
clang/lib/Sema/SemaExprCXX.cpp
clang/test/SemaCXX/warn-unused-but-set-variables-cpp.cpp
Index: clang/test/SemaCXX/warn-unused-but-set-variables-cpp.cpp
===================================================================
--- clang/test/SemaCXX/warn-unused-but-set-variables-cpp.cpp
+++ clang/test/SemaCXX/warn-unused-but-set-variables-cpp.cpp
@@ -6,6 +6,7 @@
struct __attribute__((warn_unused)) SWarnUnused {
int j;
+ void operator +=(int);
};
int f0() {
@@ -48,3 +49,16 @@
char a[x];
char b[y];
}
+
+void f3(int n) {
+ // Don't warn for overloaded compound assignment operators.
+ SWarnUnused swu;
+ swu += n;
+}
+
+template<typename T> void f4(T n) {
+ // Don't warn for (potentially) overloaded compound assignment operators in
+ // template code.
+ SWarnUnused swu;
+ swu += n;
+}
Index: clang/lib/Sema/SemaExprCXX.cpp
===================================================================
--- clang/lib/Sema/SemaExprCXX.cpp
+++ clang/lib/Sema/SemaExprCXX.cpp
@@ -7791,11 +7791,16 @@
Expr *E, llvm::DenseMap<const VarDecl *, int> &RefsMinusAssignments) {
DeclRefExpr *LHS = nullptr;
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(E)) {
- if (!BO->isAssignmentOp())
+ if (BO->getLHS()->getType()->isDependentType() ||
+ BO->getRHS()->getType()->isDependentType())
+ {
+ if (BO->getOpcode() != BO_Assign)
+ return;
+ } else if (!BO->isAssignmentOp())
return;
LHS = dyn_cast<DeclRefExpr>(BO->getLHS());
} else if (CXXOperatorCallExpr *COCE = dyn_cast<CXXOperatorCallExpr>(E)) {
- if (!COCE->isAssignmentOp())
+ if (COCE->getOperator() != OO_Equal)
return;
LHS = dyn_cast<DeclRefExpr>(COCE->getArg(0));
}
Index: clang/test/SemaCXX/warn-unused-but-set-variables-cpp.cpp
===================================================================
--- clang/test/SemaCXX/warn-unused-but-set-variables-cpp.cpp
+++ clang/test/SemaCXX/warn-unused-but-set-variables-cpp.cpp
@@ -6,6 +6,7 @@
struct __attribute__((warn_unused)) SWarnUnused {
int j;
+ void operator +=(int);
};
int f0() {
@@ -48,3 +49,16 @@
char a[x];
char b[y];
}
+
+void f3(int n) {
+ // Don't warn for overloaded compound assignment operators.
+ SWarnUnused swu;
+ swu += n;
+}
+
+template<typename T> void f4(T n) {
+ // Don't warn for (potentially) overloaded compound assignment operators in
+ // template code.
+ SWarnUnused swu;
+ swu += n;
+}
Index: clang/lib/Sema/SemaExprCXX.cpp
===================================================================
--- clang/lib/Sema/SemaExprCXX.cpp
+++ clang/lib/Sema/SemaExprCXX.cpp
@@ -7791,11 +7791,16 @@
Expr *E, llvm::DenseMap<const VarDecl *, int> &RefsMinusAssignments) {
DeclRefExpr *LHS = nullptr;
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(E)) {
- if (!BO->isAssignmentOp())
+ if (BO->getLHS()->getType()->isDependentType() ||
+ BO->getRHS()->getType()->isDependentType())
+ {
+ if (BO->getOpcode() != BO_Assign)
+ return;
+ } else if (!BO->isAssignmentOp())
return;
LHS = dyn_cast<DeclRefExpr>(BO->getLHS());
} else if (CXXOperatorCallExpr *COCE = dyn_cast<CXXOperatorCallExpr>(E)) {
- if (!COCE->isAssignmentOp())
+ if (COCE->getOperator() != OO_Equal)
return;
LHS = dyn_cast<DeclRefExpr>(COCE->getArg(0));
}
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