Implement -Wvla correctly

GCC implements -Wvla as "warn on every VLA" (this is useful to find every VLA,
for example, if they are forbidden by coding guidelines).  Currently Clang
implements -Wvla as "warn on VLA when it is an extension".

The attached patch makes our behavior match GCC.  The existing vla extwarn is
moved under -Wvla-extension and is still included into -Wgnu.

This fixes PR5953.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@173286 91177308-0d34-0410-b5e6-96231b3b80d8

7 files changed, 51 insertions, 4 deletions

diff --git a/include/clang/Basic/DiagnosticGroups.td b/include/clang/Basic/DiagnosticGroups.td
index 7709be139b..c06bbf6e14 100644
--- a/include/clang/Basic/DiagnosticGroups.td
+++ b/include/clang/Basic/DiagnosticGroups.td
@@ -317,6 +317,7 @@ def VariadicMacros : DiagGroup<"variadic-macros">;
 def VectorConversion : DiagGroup<"vector-conversion">;      // clang specific
 def VexingParse : DiagGroup<"vexing-parse">;
 def VLA : DiagGroup<"vla">;
+def VLAExtension : DiagGroup<"vla-extension">;
 def VolatileRegisterVar : DiagGroup<"volatile-register-var">;
 def Visibility : DiagGroup<"visibility">;
 def ZeroLengthArray : DiagGroup<"zero-length-array">;
@@ -473,7 +474,7 @@ def C11 : DiagGroup<"c11-extensions">;
 def C99 : DiagGroup<"c99-extensions">;
 
 // A warning group for warnings about GCC extensions.
-def GNU : DiagGroup<"gnu", [GNUDesignator, VLA, ZeroLengthArray]>;
+def GNU : DiagGroup<"gnu", [GNUDesignator, VLAExtension, ZeroLengthArray]>;
 // A warning group for warnings about code that clang accepts but gcc doesn't.
 def GccCompat : DiagGroup<"gcc-compat">;
 
diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index 2683ac0543..be6ef607ed 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -75,7 +75,9 @@ def warn_double_const_requires_fp64 : Warning<
 
 // C99 variable-length arrays
 def ext_vla : Extension<"variable length arrays are a C99 feature">,
-  InGroup<VLA>;
+  InGroup<VLAExtension>;
+def warn_vla_used : Warning<"variable length array used">,
+  InGroup<VLA>, DefaultIgnore;
 def err_vla_non_pod : Error<"variable length array of non-POD element type %0">;
 def err_vla_in_sfinae : Error<
   "variable length array cannot be formed during template argument deduction">;
diff --git a/lib/Sema/SemaType.cpp b/lib/Sema/SemaType.cpp
index dbee50a4c9..f6cad26989 100644
--- a/lib/Sema/SemaType.cpp
+++ b/lib/Sema/SemaType.cpp
@@ -1496,6 +1496,11 @@ QualType Sema::BuildArrayType(QualType T, ArrayType::ArraySizeModifier ASM,
                                      : diag::ext_c99_array_usage) << ASM;
   }
 
+  if (T->isVariableArrayType()) {
+    // Warn about VLAs for -Wvla.
+    Diag(Loc, diag::warn_vla_used);
+  }
+
   return T;
 }
 
diff --git a/test/Sema/warn-vla.c b/test/Sema/warn-vla.c
new file mode 100644
index 0000000000..01fe45173b
--- /dev/null
+++ b/test/Sema/warn-vla.c
@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -std=c99 -fsyntax-only -verify -Wvla %s
+// RUN: %clang_cc1 -std=c89 -fsyntax-only -verify -Wvla %s
+
+void test1(int n) {
+  int v[n]; // expected-warning {{variable length array used}}
+}
+
+void test2(int n, int v[n]) { // expected-warning {{variable length array used}}
+}
+
+void test3(int n, int v[n]); // expected-warning {{variable length array used}}
+
diff --git a/test/SemaCXX/c99-variable-length-array-cxx11.cpp b/test/SemaCXX/c99-variable-length-array-cxx11.cpp
index b740e39775..03cf28388d 100644
--- a/test/SemaCXX/c99-variable-length-array-cxx11.cpp
+++ b/test/SemaCXX/c99-variable-length-array-cxx11.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -fsyntax-only -verify -std=c++11 -Wvla %s
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++11 -Wvla-extension %s
 struct StillPOD {
   StillPOD() = default;
 };
diff --git a/test/SemaCXX/c99-variable-length-array.cpp b/test/SemaCXX/c99-variable-length-array.cpp
index 7773c0849b..de9c11e565 100644
--- a/test/SemaCXX/c99-variable-length-array.cpp
+++ b/test/SemaCXX/c99-variable-length-array.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -fsyntax-only -verify -Wvla %s
+// RUN: %clang_cc1 -fsyntax-only -verify -Wvla-extension %s
 struct NonPOD {
   NonPOD();
 };
diff --git a/test/SemaCXX/warn-vla.cpp b/test/SemaCXX/warn-vla.cpp
new file mode 100644
index 0000000000..081f1c7b21
--- /dev/null
+++ b/test/SemaCXX/warn-vla.cpp
@@ -0,0 +1,27 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -Wvla %s
+
+void test1(int n) {
+  int v[n]; // expected-warning {{variable length array used}}
+}
+
+void test2(int n, int v[n]) { // expected-warning {{variable length array used}}
+}
+
+void test3(int n, int v[n]); // expected-warning {{variable length array used}}
+
+template<typename T>
+void test4(int n) {
+  int v[n]; // expected-warning {{variable length array used}}
+}
+
+template<typename T>
+void test5(int n, int v[n]) { // expected-warning {{variable length array used}}
+}
+
+template<typename T>
+void test6(int n, int v[n]); // expected-warning {{variable length array used}}
+
+template<typename T>
+void test7(int n, T v[n]) { // expected-warning {{variable length array used}}
+}
+