[PATCH] D100136: Allow applying attributes to subset of allowed subjects.

[Artem Belevich via Phabricator via cfe-commits]

tra created this revision.
tra added reviewers: rsmith, arphaman.
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tra requested review of this revision.
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The original intent of enforcing exact match between `apply_to` and the attribute's was to 
`ensure that the user will know what declarations receive the attribute. If the compiler changes the set of allowed attributes in the future`.
https://reviews.llvm.org/D30009?id=88764#inline-260744

However, the exact match, as implemented now, is too conservative. E.g. it does not allow using `apply_to=variables(is_global)` with an attribute which has `SubjectList<[Var]>`.
Applying an attribute to a subset of the allowed subjects should also be allowed.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D100136

Files:
  clang/lib/Sema/SemaAttr.cpp
  clang/test/Parser/pragma-attribute.cpp


Index: clang/test/Parser/pragma-attribute.cpp
===================================================================
--- clang/test/Parser/pragma-attribute.cpp
+++ clang/test/Parser/pragma-attribute.cpp
@@ -195,3 +195,12 @@
 #pragma clang attribute pop
 #pragma clang attribute push([[clang::uninitialized]], apply_to = any(variable(is_parameter), variable(unless(is_parameter)))) // expected-error {{attribute 'uninitialized' can't be applied to 'variable(is_parameter)', and 'variable(unless(is_parameter))'}}
 #pragma clang attribute pop
+// We're allowed to apply attributes to subsets of allowed subjects.
+#pragma clang attribute push([[clang::no_destroy]], apply_to = variable)
+#pragma clang attribute pop
+#pragma clang attribute push([[clang::no_destroy]], apply_to = variable(is_thread_local))
+#pragma clang attribute pop
+#pragma clang attribute push([[clang::no_destroy]], apply_to = variable(is_global))
+#pragma clang attribute pop
+#pragma clang attribute push([[clang::no_destroy]], apply_to = any(variable(is_parameter), variable(unless(is_parameter))))
+#pragma clang attribute pop
Index: clang/lib/Sema/SemaAttr.cpp
===================================================================
--- clang/lib/Sema/SemaAttr.cpp
+++ clang/lib/Sema/SemaAttr.cpp
@@ -875,12 +875,33 @@
     }
     Rules.clear();
   } else {
-    for (const auto &Rule : StrictSubjectMatchRuleSet) {
-      if (Rules.erase(Rule.first)) {
+    // Each rule in Rules must be a strict subset of the attribute's
+    // SubjectMatch rules.  I.e. we're allowed to use
+    // `apply_to=variables(is_global)` on an attrubute with SubjectList<[Var]>,
+    // but should not allow `apply_to=variables` on an attribute which has
+    // `SubjectList<[GlobalVar]>`.
+    for (const auto &StrictRule : StrictSubjectMatchRuleSet) {
+      // First, check for exact match.
+      if (Rules.erase(StrictRule.first)) {
         // Add the rule to the set of attribute receivers only if it's supported
         // in the current language mode.
-        if (Rule.second)
-          SubjectMatchRules.push_back(Rule.first);
+        if (StrictRule.second)
+          SubjectMatchRules.push_back(StrictRule.first);
+      }
+    }
+    // Check remaining rules for subset matches.
+    auto RulesToCheck = Rules;
+    for (const auto &Rule : RulesToCheck) {
+      attr::SubjectMatchRule MatchRule = attr::SubjectMatchRule(Rule.first);
+      if (auto ParentRule = getParentAttrMatcherRule(MatchRule)) {
+        if (llvm::any_of(StrictSubjectMatchRuleSet,
+                         [ParentRule](const auto &StrictRule) {
+                           return StrictRule.first == *ParentRule &&
+                                  StrictRule.second; // IsEnabled
+                         })) {
+          SubjectMatchRules.push_back(MatchRule);
+          Rules.erase(MatchRule);
+        }
       }
     }
   }


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