[Clang] [Parser] Support [[omp::assume]] (#84582)

This pr implements the `[[omp::assume]]` spelling for the `__attribute__((assume))` attribute. It does not change anything about how that attribute is handled by the rest of Clang.

Author: Sirraide

clang/docs/ReleaseNotes.rst

@@ -500,6 +500,11 @@ Python Binding Changes
 
 - Exposed `CXRewriter` API as `class Rewriter`.
 
+OpenMP Support
+--------------
+
+- Added support for the `[[omp::assume]]` attribute.
+
 Additional Information
 ======================
 

clang/include/clang/Basic/Attr.td

@@ -4159,7 +4159,7 @@ def OMPDeclareVariant : InheritableAttr {
 }
 
 def OMPAssume : InheritableAttr {
-  let Spellings = [Clang<"assume">];
+  let Spellings = [Clang<"assume">, CXX11<"omp", "assume">];
   let Subjects = SubjectList<[Function, ObjCMethod]>;
   let InheritEvenIfAlreadyPresent = 1;
   let Documentation = [OMPAssumeDocs];

clang/lib/Basic/Attributes.cpp

@@ -47,8 +47,12 @@ int clang::hasAttribute(AttributeCommonInfo::Syntax Syntax,
   // attributes. We support those, but not through the typical attribute
   // machinery that goes through TableGen. We support this in all OpenMP modes
   // so long as double square brackets are enabled.
-  if (LangOpts.OpenMP && ScopeName == "omp")
-    return (Name == "directive" || Name == "sequence") ? 1 : 0;
+  //
+  // Other OpenMP attributes (e.g. [[omp::assume]]) are handled via the
+  // regular attribute parsing machinery.
+  if (LangOpts.OpenMP && ScopeName == "omp" &&
+      (Name == "directive" || Name == "sequence"))
+    return 1;
 
   int res = hasAttributeImpl(Syntax, Name, ScopeName, Target, LangOpts);
   if (res)

clang/lib/Parse/ParseDeclCXX.cpp

@@ -4634,7 +4634,9 @@ bool Parser::ParseCXX11AttributeArgs(
     return true;
   }
 
-  if (ScopeName && ScopeName->isStr("omp")) {
+  // [[omp::directive]] and [[omp::sequence]] need special handling.
+  if (ScopeName && ScopeName->isStr("omp") &&
+      (AttrName->isStr("directive") || AttrName->isStr("sequence"))) {
     Diag(AttrNameLoc, getLangOpts().OpenMP >= 51
                           ? diag::warn_omp51_compat_attributes
                           : diag::ext_omp_attributes);

clang/test/OpenMP/attr-assume.cpp

@@ -0,0 +1,13 @@
+// RUN: %clang_cc1 -fsyntax-only -fopenmp -verify %s
+[[omp::assume(3)]] void f1(); // expected-error {{expected string literal as argument of 'assume' attribute}}
+[[omp::assume(int)]] void f2(); // expected-error {{expected string literal as argument of 'assume' attribute}}
+[[omp::assume(for)]] void f3(); // expected-error {{expected string literal as argument of 'assume' attribute}}
+[[omp::assume("QQQQ")]] void f4(); // expected-warning {{unknown assumption string 'QQQQ'; attribute is potentially ignored}}
+[[omp::assume("omp_no_openmp")]] void f5();
+[[omp::assume("omp_noopenmp")]] void f6(); // expected-warning {{unknown assumption string 'omp_noopenmp' may be misspelled; attribute is potentially ignored, did you mean 'omp_no_openmp'?}}
+[[omp::assume("omp_no_openmp_routine")]] void f7(); // expected-warning {{unknown assumption string 'omp_no_openmp_routine' may be misspelled; attribute is potentially ignored, did you mean 'omp_no_openmp_routines'?}}
+[[omp::assume("omp_no_openmp1")]] void f8(); // expected-warning {{unknown assumption string 'omp_no_openmp1' may be misspelled; attribute is potentially ignored, did you mean 'omp_no_openmp'?}}
+[[omp::assume("omp_no_openmp", "omp_no_openmp")]] void f9(); // expected-error {{'assume' attribute takes one argument}}
+
+[[omp::assume(3)]] int g1; // expected-error {{expected string literal as argument of 'assume' attribute}}
+[[omp::assume("omp_no_openmp")]] int g2; // expected-warning {{'assume' attribute only applies to functions and Objective-C methods}}