r316083 - Enable support for the [[fallthrough]] attribute from WG14 N2052 when enabling double square bracket attributes in C code.

Aaron Ballman via cfe-commits cfe-commits at lists.llvm.org
Wed Oct 18 07:33:27 PDT 2017


Author: aaronballman
Date: Wed Oct 18 07:33:27 2017
New Revision: 316083

URL: http://llvm.org/viewvc/llvm-project?rev=316083&view=rev
Log:
Enable support for the [[fallthrough]] attribute from WG14 N2052 when enabling double square bracket attributes in C code.

Added:
    cfe/trunk/test/Sema/c2x-fallthrough.c
Modified:
    cfe/trunk/include/clang/Basic/Attr.td
    cfe/trunk/lib/Sema/AnalysisBasedWarnings.cpp

Modified: cfe/trunk/include/clang/Basic/Attr.td
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/Attr.td?rev=316083&r1=316082&r2=316083&view=diff
==============================================================================
--- cfe/trunk/include/clang/Basic/Attr.td (original)
+++ cfe/trunk/include/clang/Basic/Attr.td Wed Oct 18 07:33:27 2017
@@ -1009,7 +1009,7 @@ def ExtVectorType : Attr {
 }
 
 def FallThrough : StmtAttr {
-  let Spellings = [CXX11<"", "fallthrough", 201603>,
+  let Spellings = [CXX11<"", "fallthrough", 201603>, C2x<"", "fallthrough">,
                    CXX11<"clang", "fallthrough">];
 //  let Subjects = [NullStmt];
   let Documentation = [FallthroughDocs];

Modified: cfe/trunk/lib/Sema/AnalysisBasedWarnings.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/AnalysisBasedWarnings.cpp?rev=316083&r1=316082&r2=316083&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/AnalysisBasedWarnings.cpp (original)
+++ cfe/trunk/lib/Sema/AnalysisBasedWarnings.cpp Wed Oct 18 07:33:27 2017
@@ -1291,16 +1291,15 @@ static StringRef getFallthroughAttrSpell
 
 static void DiagnoseSwitchLabelsFallthrough(Sema &S, AnalysisDeclContext &AC,
                                             bool PerFunction) {
-  // Only perform this analysis when using C++11.  There is no good workflow
-  // for this warning when not using C++11.  There is no good way to silence
-  // the warning (no attribute is available) unless we are using C++11's support
-  // for generalized attributes.  Once could use pragmas to silence the warning,
-  // but as a general solution that is gross and not in the spirit of this
-  // warning.
+  // Only perform this analysis when using [[]] attributes. There is no good
+  // workflow for this warning when not using C++11. There is no good way to
+  // silence the warning (no attribute is available) unless we are using 
+  // [[]] attributes. One could use pragmas to silence the warning, but as a
+  // general solution that is gross and not in the spirit of this warning.
   //
-  // NOTE: This an intermediate solution.  There are on-going discussions on
+  // NOTE: This an intermediate solution. There are on-going discussions on
   // how to properly support this warning outside of C++11 with an annotation.
-  if (!AC.getASTContext().getLangOpts().CPlusPlus11)
+  if (!AC.getASTContext().getLangOpts().DoubleSquareBracketAttributes)
     return;
 
   FallthroughMapper FM(S);

Added: cfe/trunk/test/Sema/c2x-fallthrough.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/c2x-fallthrough.c?rev=316083&view=auto
==============================================================================
--- cfe/trunk/test/Sema/c2x-fallthrough.c (added)
+++ cfe/trunk/test/Sema/c2x-fallthrough.c Wed Oct 18 07:33:27 2017
@@ -0,0 +1,75 @@
+// RUN: %clang_cc1 -fsyntax-only -fdouble-square-bracket-attributes -verify %s
+
+void f(int n) {
+  switch (n) {
+  case 0:
+    n += 1;
+    [[fallthrough]]; // ok
+  case 1:
+    if (n) {
+      [[fallthrough]]; // ok
+    } else {
+      return;
+    }
+  case 2:
+    for (int n = 0; n != 10; ++n)
+      [[fallthrough]]; // expected-error {{does not directly precede switch label}}
+  case 3:
+    while (1)
+      [[fallthrough]]; // expected-error {{does not directly precede switch label}}
+  case 4:
+    while (0)
+      [[fallthrough]]; // expected-error {{does not directly precede switch label}}
+  case 5:
+    do [[fallthrough]]; while (1); // expected-error {{does not directly precede switch label}}
+  case 6:
+    do [[fallthrough]]; while (0); // expected-error {{does not directly precede switch label}}
+  case 7:
+    switch (n) {
+    case 0:
+      // FIXME: This should be an error, even though the next thing we do is to
+      // fall through in an outer switch statement.
+      [[fallthrough]];
+    }
+  case 8:
+    [[fallthrough]]; // expected-error {{does not directly precede switch label}}
+    goto label;
+  label:
+  case 9:
+    n += 1;
+  case 10: // no warning, -Wimplicit-fallthrough is not enabled in this test, and does not need to
+           // be enabled for these diagnostics to be produced.
+    break;
+  }
+}
+
+[[fallthrough]] typedef int n; // expected-error {{'fallthrough' attribute cannot be applied to a declaration}}
+typedef int [[fallthrough]] n; // expected-error {{'fallthrough' attribute cannot be applied to types}}
+typedef int n [[fallthrough]]; // expected-error {{'fallthrough' attribute cannot be applied to a declaration}}
+
+enum [[fallthrough]] E { // expected-error {{'fallthrough' attribute cannot be applied to a declaration}}
+  One
+};
+struct [[fallthrough]] S { // expected-error {{'fallthrough' attribute cannot be applied to a declaration}}
+  int i;
+};
+
+[[fallthrough]] // expected-error {{'fallthrough' attribute cannot be applied to a declaration}}
+void g(void) {
+  [[fallthrough]] int n; // expected-error {{'fallthrough' attribute cannot be applied to a declaration}}
+  [[fallthrough]] ++n; // expected-error-re {{{{^}}fallthrough attribute is only allowed on empty statements}}
+
+  switch (n) {
+    // FIXME: This should be an error.
+    [[fallthrough]];
+    return;
+
+  case 0:
+    [[fallthrough, fallthrough]]; // expected-error {{multiple times}}
+  case 1:
+    [[fallthrough(0)]]; // expected-error {{argument list}}
+  case 2:
+    break;
+  }
+}
+




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