incertia created this revision.
incertia added reviewers: rjmccall, rsmith.
incertia added a project: clang.
Herald added a subscriber: cfe-commits.
To my understanding, the contents of a condition will always be implicitly
casted to an rvalue before evaluation. Thus, moving the check to
PerformImplicitConversion should be correct. We can also check the more general
case here of general boolean expressions. This should catch a few more cases vs
gcc. The only examples that I can come up with that will bypass this check
would be
bool & f(bool &b) { return b = true; }
f(b = false); // b = false is an lvalue, the reference passed into the
function is an lvalue, and the reference returned out is an lvalue, which
causes no warnings.
Clearly passing in the result of an assignment to a function is not very good,
so we should probably have a separate check for that. On the other hand, I have
no idea if we should even warn on returning the (boolean) result of assigning
to a boolean reference or how such a check would be implemented, outside of
brute force within ActOnReturnStmt, which would collide with the warnings in
PerformImplicitConversion.
Repository:
rC Clang
https://reviews.llvm.org/D45401
Files:
lib/Sema/SemaExpr.cpp
lib/Sema/SemaExprCXX.cpp
Index: lib/Sema/SemaExprCXX.cpp
===================================================================
--- lib/Sema/SemaExprCXX.cpp
+++ lib/Sema/SemaExprCXX.cpp
@@ -3860,6 +3860,10 @@
case ICK_Lvalue_To_Rvalue: {
assert(From->getObjectKind() != OK_ObjCProperty);
+ if (SCS.Second == ICK_Boolean_Conversion ||
+ From->getType() == Context.BoolTy) {
+ DiagnoseAssignmentAsCondition(From->IgnoreImpCasts());
+ }
ExprResult FromRes = DefaultLvalueConversion(From);
assert(!FromRes.isInvalid() && "Can't perform deduced conversion?!");
From = FromRes.get();
Index: lib/Sema/SemaExpr.cpp
===================================================================
--- lib/Sema/SemaExpr.cpp
+++ lib/Sema/SemaExpr.cpp
@@ -15409,7 +15409,10 @@
ExprResult Sema::CheckBooleanCondition(SourceLocation Loc, Expr *E,
bool IsConstexpr) {
- DiagnoseAssignmentAsCondition(E);
+ // an assignment always produces an lvalue, and we now check this inside
+ // PerformImplicitConversion, as conditions will always be implicitly
+ // converted to an rvalue
+ // DiagnoseAssignmentAsCondition(E);
if (ParenExpr *parenE = dyn_cast<ParenExpr>(E))
DiagnoseEqualityWithExtraParens(parenE);
Index: lib/Sema/SemaExprCXX.cpp
===================================================================
--- lib/Sema/SemaExprCXX.cpp
+++ lib/Sema/SemaExprCXX.cpp
@@ -3860,6 +3860,10 @@
case ICK_Lvalue_To_Rvalue: {
assert(From->getObjectKind() != OK_ObjCProperty);
+ if (SCS.Second == ICK_Boolean_Conversion ||
+ From->getType() == Context.BoolTy) {
+ DiagnoseAssignmentAsCondition(From->IgnoreImpCasts());
+ }
ExprResult FromRes = DefaultLvalueConversion(From);
assert(!FromRes.isInvalid() && "Can't perform deduced conversion?!");
From = FromRes.get();
Index: lib/Sema/SemaExpr.cpp
===================================================================
--- lib/Sema/SemaExpr.cpp
+++ lib/Sema/SemaExpr.cpp
@@ -15409,7 +15409,10 @@
ExprResult Sema::CheckBooleanCondition(SourceLocation Loc, Expr *E,
bool IsConstexpr) {
- DiagnoseAssignmentAsCondition(E);
+ // an assignment always produces an lvalue, and we now check this inside
+ // PerformImplicitConversion, as conditions will always be implicitly
+ // converted to an rvalue
+ // DiagnoseAssignmentAsCondition(E);
if (ParenExpr *parenE = dyn_cast<ParenExpr>(E))
DiagnoseEqualityWithExtraParens(parenE);
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