ychen created this revision.
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GCC/MSVC diagnoses in such cases, probably it makes sense to do the
same for Clang.
https://godbolt.org/z/7zxb8Tx96
It actually generated the warning internally, however since
`Sema::DiagnoseUnusedExprResult` called `Sema::DiagRuntimeBehavior` which
claims that "Relevant diagnostics should be produced by constant
evaluation.". So directly diagnose in `Sema::DiagnoseUnusedExprResult`
for constant evaluation context cases.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D103938
Files:
clang/lib/Sema/SemaStmt.cpp
clang/test/SemaCXX/warn-unused-value.cpp
Index: clang/test/SemaCXX/warn-unused-value.cpp
===================================================================
--- clang/test/SemaCXX/warn-unused-value.cpp
+++ clang/test/SemaCXX/warn-unused-value.cpp
@@ -138,3 +138,10 @@
(void)arr3;
(void)arr4;
}
+
+#if __cplusplus >= 201103L // C++11 or later
+namespace test5 {
+int v[(5, 6)]; // expected-warning {{expression result
unused}}
+auto p1 = new double[4][(5, 6)]; // expected-warning {{expression result
unused}}
+} // namespace test5
+#endif
Index: clang/lib/Sema/SemaStmt.cpp
===================================================================
--- clang/lib/Sema/SemaStmt.cpp
+++ clang/lib/Sema/SemaStmt.cpp
@@ -379,6 +379,12 @@
return;
}
+ if (ExprEvalContexts.back().Context ==
+ ExpressionEvaluationContext::ConstantEvaluated) {
+ Diag(Loc, DiagID) << R1 << R2;
+ return;
+ }
+
DiagRuntimeBehavior(Loc, nullptr, PDiag(DiagID) << R1 << R2);
}
Index: clang/test/SemaCXX/warn-unused-value.cpp
===================================================================
--- clang/test/SemaCXX/warn-unused-value.cpp
+++ clang/test/SemaCXX/warn-unused-value.cpp
@@ -138,3 +138,10 @@
(void)arr3;
(void)arr4;
}
+
+#if __cplusplus >= 201103L // C++11 or later
+namespace test5 {
+int v[(5, 6)]; // expected-warning {{expression result unused}}
+auto p1 = new double[4][(5, 6)]; // expected-warning {{expression result unused}}
+} // namespace test5
+#endif
Index: clang/lib/Sema/SemaStmt.cpp
===================================================================
--- clang/lib/Sema/SemaStmt.cpp
+++ clang/lib/Sema/SemaStmt.cpp
@@ -379,6 +379,12 @@
return;
}
+ if (ExprEvalContexts.back().Context ==
+ ExpressionEvaluationContext::ConstantEvaluated) {
+ Diag(Loc, DiagID) << R1 << R2;
+ return;
+ }
+
DiagRuntimeBehavior(Loc, nullptr, PDiag(DiagID) << R1 << R2);
}
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