Comment the weird behavior of __has_feature(is_empty) and __has_feature(is_pod)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@136788 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Lex/PPMacroExpansion.cpp b/lib/Lex/PPMacroExpansion.cpp
index 7046c5f2fdaf5fc69549e2e6b4b30dd18df7d4de..a4b6cc9db85721249ff34a5e67a057a949f3cf25 100644 (file)
--- a/lib/Lex/PPMacroExpansion.cpp
+++ b/lib/Lex/PPMacroExpansion.cpp
@@ -639,6 +639,10 @@ static bool HasFeature(const Preprocessor &PP, const IdentifierInfo *II) {
            .Case("is_base_of", LangOpts.CPlusPlus)
            .Case("is_class", LangOpts.CPlusPlus)
            .Case("is_convertible_to", LangOpts.CPlusPlus)
+            // __is_empty is available only if the horrible
+            // "struct __is_empty" parsing hack hasn't been needed in this
+            // translation unit. If it has, __is_empty reverts to a normal
+            // identifier and __has_feature(is_empty) evaluates false.
            .Case("is_empty", 
                  LangOpts.CPlusPlus && 
                  PP.getIdentifierInfo("__is_empty")->getTokenID()
@@ -646,6 +650,10 @@ static bool HasFeature(const Preprocessor &PP, const IdentifierInfo *II) {
            .Case("is_enum", LangOpts.CPlusPlus)
            .Case("is_literal", LangOpts.CPlusPlus)
            .Case("is_standard_layout", LangOpts.CPlusPlus)
+           // __is_pod is available only if the horrible
+           // "struct __is_pod" parsing hack hasn't been needed in this
+           // translation unit. If it has, __is_pod reverts to a normal
+           // identifier and __has_feature(is_pod) evaluates false.
            .Case("is_pod", 
                  LangOpts.CPlusPlus && 
                  PP.getIdentifierInfo("__is_pod")->getTokenID()