[OpenACC] Implement 'collapse' clause parsing.

The 'collapse' clause takes an optional 'force:' followed by an integer
constant expression.  For now, parse this as an assignment expression,
and we'll check it for value/ICE later.

clang/include/clang/Basic/OpenACCKinds.h

@@ -217,6 +217,8 @@ enum class OpenACCClauseKind {
   /// 'reduction' clause, allowed on Parallel, Serial, Loop, and the combined
   /// constructs.
   Reduction,
+  /// 'collapse' clause, allowed on 'loop' and Combined constructs.
+  Collapse,
 
   /// Represents an invalid clause, for the purposes of parsing.
   Invalid,
@@ -312,6 +314,9 @@ inline const StreamingDiagnostic &operator<<(const StreamingDiagnostic &Out,
   case OpenACCClauseKind::Reduction:
     return Out << "reduction";
 
+  case OpenACCClauseKind::Collapse:
+    return Out << "collapse";
+
   case OpenACCClauseKind::Invalid:
     return Out << "<invalid>";
   }

clang/lib/Parse/ParseOpenACC.cpp

@@ -92,6 +92,7 @@ OpenACCClauseKind getOpenACCClauseKind(Token Tok) {
       .Case("attach", OpenACCClauseKind::Attach)
       .Case("auto", OpenACCClauseKind::Auto)
       .Case("create", OpenACCClauseKind::Create)
+      .Case("collapse", OpenACCClauseKind::Collapse)
       .Case("copy", OpenACCClauseKind::Copy)
       .Case("copyin", OpenACCClauseKind::CopyIn)
       .Case("copyout", OpenACCClauseKind::CopyOut)
@@ -151,6 +152,7 @@ enum class OpenACCSpecialTokenKind {
   DevNum,
   Queues,
   Zero,
+  Force,
 };
 
 bool isOpenACCSpecialToken(OpenACCSpecialTokenKind Kind, Token Tok) {
@@ -166,6 +168,8 @@ bool isOpenACCSpecialToken(OpenACCSpecialTokenKind Kind, Token Tok) {
     return Tok.getIdentifierInfo()->isStr("queues");
   case OpenACCSpecialTokenKind::Zero:
     return Tok.getIdentifierInfo()->isStr("zero");
+  case OpenACCSpecialTokenKind::Force:
+    return Tok.getIdentifierInfo()->isStr("force");
   }
   llvm_unreachable("Unknown 'Kind' Passed");
 }
@@ -462,6 +466,7 @@ ClauseParensKind getClauseParensKind(OpenACCDirectiveKind DirKind,
   case OpenACCClauseKind::Link:
   case OpenACCClauseKind::Host:
   case OpenACCClauseKind::Reduction:
+  case OpenACCClauseKind::Collapse:
     return ClauseParensKind::Required;
 
   case OpenACCClauseKind::Auto:
@@ -654,6 +659,15 @@ bool Parser::ParseOpenACCClauseParams(OpenACCDirectiveKind DirKind,
       if (ParseOpenACCClauseVarList(Kind))
         return true;
       break;
+    case OpenACCClauseKind::Collapse: {
+      tryParseAndConsumeSpecialTokenKind(*this, OpenACCSpecialTokenKind::Force,
+                                         Kind);
+      ExprResult NumLoops =
+          getActions().CorrectDelayedTyposInExpr(ParseAssignmentExpression());
+      if (NumLoops.isInvalid())
+        return true;
+      break;
+    }
     default:
       llvm_unreachable("Not a required parens type?");
     }

clang/test/ParserOpenACC/parse-clauses.c

@@ -54,6 +54,45 @@ void func() {
   // expected-warning@+1{{OpenACC directives not yet implemented, pragma ignored}}
 #pragma acc loop seq,
 
+  // expected-error@+2{{expected '('}}
+  // expected-warning@+1{{OpenACC directives not yet implemented, pragma ignored}}
+#pragma acc loop collapse
+  for(;;){}
+
+  // expected-error@+2{{expected expression}}
+  // expected-warning@+1{{OpenACC directives not yet implemented, pragma ignored}}
+#pragma acc loop collapse()
+  for(;;){}
+
+  // expected-error@+3{{invalid tag 'unknown' on 'collapse' clause}}
+  // expected-error@+2{{expected expression}}
+  // expected-warning@+1{{OpenACC directives not yet implemented, pragma ignored}}
+#pragma acc loop collapse(unknown:)
+  for(;;){}
+
+  // expected-error@+2{{expected expression}}
+  // expected-warning@+1{{OpenACC directives not yet implemented, pragma ignored}}
+#pragma acc loop collapse(force:)
+  for(;;){}
+
+  // expected-error@+2{{invalid tag 'unknown' on 'collapse' clause}}
+  // expected-warning@+1{{OpenACC directives not yet implemented, pragma ignored}}
+#pragma acc loop collapse(unknown:5)
+  for(;;){}
+
+  // expected-warning@+1{{OpenACC directives not yet implemented, pragma ignored}}
+#pragma acc loop collapse(force:5)
+  for(;;){}
+
+  // expected-warning@+1{{OpenACC directives not yet implemented, pragma ignored}}
+#pragma acc loop collapse(5)
+  for(;;){}
+
+  // expected-error@+3{{expected ')'}}
+  // expected-note@+2{{to match this '('}}
+  // expected-warning@+1{{OpenACC directives not yet implemented, pragma ignored}}
+#pragma acc loop collapse(5, 6)
+  for(;;){}
 }
 
 void DefaultClause() {

clang/test/ParserOpenACC/parse-clauses.cpp

@@ -0,0 +1,20 @@
+// RUN: %clang_cc1 %s -verify -fopenacc
+
+template<unsigned I, typename T>
+void templ() {
+  // expected-warning@+1{{OpenACC directives not yet implemented, pragma ignored}}
+#pragma acc loop collapse(I)
+  for(;;){}
+
+  // expected-warning@+1{{OpenACC directives not yet implemented, pragma ignored}}
+#pragma acc loop collapse(T::value)
+  for(;;){}
+}
+
+struct S {
+  static constexpr unsigned value = 5;
+};
+
+void use() {
+  templ<7, S>();
+}