[OpenACC][NFC] AST changes for Reduction combiner (llvm#162573)

This is the first patch of a handful to get the reduction combiner
recipe lowering properly. THIS patch is NFC as it doesn't actually
change anything except the structure of the AST.

For each 'combiner' recipe we need a 'LHS' 'RHS' and expression to
represent the operation.

Each var-reference can have 1 or more combiners.

IF it is a plain scalar, or a struct with the proper operator, or an
array of either of those, there will be 1.

HOWEVER, aggregates without the proper operator are supposed to be
broken down and done from their elements (which can only be scalars). In
this case, we will represent 1 'combiner' recipe per field-decl.

This patch only puts the infrastructure in place to do so, future
patches wll do the work to fill this in.

Author: erichkeane

clang/include/clang/AST/OpenACCClause.h

@@ -1280,13 +1280,31 @@ class OpenACCCreateClause final
 // 'main' declaration used for initializaiton, which is fixed. 
 struct OpenACCReductionRecipe {
   VarDecl *AllocaDecl;
-  // TODO: OpenACC: this should eventually have the operations here too.
 
-  OpenACCReductionRecipe(VarDecl *A) : AllocaDecl(A) {}
+  // A combiner recipe is represented by an operation expression.  However, in
+  // order to generate these properly, we have to make up a LHS and a RHS
+  // expression for the purposes of generation.
+  struct CombinerRecipe {
+    VarDecl *LHS;
+    VarDecl *RHS;
+    Expr *Op;
+  };
+
+  // Contains a collection of the recipe elements we need for the combiner:
+  // -For Scalars, there will be 1 element, just the combiner for that scalar.
+  // -For a struct with a valid operator, this will be 1 element, just that
+  //  call.
+  // -For a struct without the operator, this will be 1 element per field, which
+  //  should be the combiner for that element.
+  // -For an array of any of the above, it will be the above for the element.
+  llvm::SmallVector<CombinerRecipe, 1> CombinerRecipes;
+
+  OpenACCReductionRecipe(VarDecl *A, llvm::ArrayRef<CombinerRecipe> Combiners)
+      : AllocaDecl(A), CombinerRecipes(Combiners) {}
 
   bool isSet() const { return AllocaDecl; }
   static OpenACCReductionRecipe Empty() {
-    return OpenACCReductionRecipe(/*AllocaDecl=*/nullptr);
+    return OpenACCReductionRecipe(/*AllocaDecl=*/nullptr, {});
   }
 };
 

clang/lib/AST/StmtProfile.cpp

@@ -2769,10 +2769,19 @@ void OpenACCClauseProfiler::VisitReductionClause(
 
   for (auto &Recipe : Clause.getRecipes()) {
     Profiler.VisitDecl(Recipe.AllocaDecl);
+
     // TODO: OpenACC: Make sure we remember to update this when we figure out
     // what we're adding for the operation recipe, in the meantime, a static
     // assert will make sure we don't add something.
-    static_assert(sizeof(OpenACCReductionRecipe) == sizeof(int *));
+    static_assert(sizeof(OpenACCReductionRecipe::CombinerRecipe) ==
+                  3 * sizeof(int *));
+    for (auto &CombinerRecipe : Recipe.CombinerRecipes) {
+      if (CombinerRecipe.Op) {
+        Profiler.VisitDecl(CombinerRecipe.LHS);
+        Profiler.VisitDecl(CombinerRecipe.RHS);
+        Profiler.VisitStmt(CombinerRecipe.Op);
+      }
+    }
   }
 }
 

clang/lib/Sema/SemaOpenACC.cpp

@@ -2946,5 +2946,5 @@ OpenACCReductionRecipe SemaOpenACC::CreateReductionInitRecipe(
     AllocaDecl->setInit(Init.get());
     AllocaDecl->setInitStyle(VarDecl::CallInit);
   }
-  return OpenACCReductionRecipe(AllocaDecl);
+  return OpenACCReductionRecipe(AllocaDecl, {});
 }

clang/lib/Serialization/ASTReader.cpp

@@ -13009,9 +13009,22 @@ OpenACCClause *ASTRecordReader::readOpenACCClause() {
     llvm::SmallVector<OpenACCReductionRecipe> RecipeList;
 
     for (unsigned I = 0; I < VarList.size(); ++I) {
-      static_assert(sizeof(OpenACCReductionRecipe) == sizeof(int *));
       VarDecl *Recipe = readDeclAs<VarDecl>();
-      RecipeList.push_back({Recipe});
+
+      static_assert(sizeof(OpenACCReductionRecipe::CombinerRecipe) ==
+                    3 * sizeof(int *));
+
+      llvm::SmallVector<OpenACCReductionRecipe::CombinerRecipe> Combiners;
+      unsigned NumCombiners = readInt();
+      for (unsigned I = 0; I < NumCombiners; ++I) {
+        VarDecl *LHS = readDeclAs<VarDecl>();
+        VarDecl *RHS = readDeclAs<VarDecl>();
+        Expr *Op = readExpr();
+
+        Combiners.push_back({LHS, RHS, Op});
+      }
+
+      RecipeList.push_back({Recipe, Combiners});
     }
 
     return OpenACCReductionClause::Create(getContext(), BeginLoc, LParenLoc, Op,

clang/lib/Serialization/ASTWriter.cpp

@@ -8925,8 +8925,17 @@ void ASTRecordWriter::writeOpenACCClause(const OpenACCClause *C) {
     writeOpenACCVarList(RC);
 
     for (const OpenACCReductionRecipe &R : RC->getRecipes()) {
-      static_assert(sizeof(OpenACCReductionRecipe) == 1 * sizeof(int *));
       AddDeclRef(R.AllocaDecl);
+
+      static_assert(sizeof(OpenACCReductionRecipe::CombinerRecipe) ==
+                    3 * sizeof(int *));
+      writeUInt32(R.CombinerRecipes.size());
+
+      for (auto &CombinerRecipe : R.CombinerRecipes) {
+        AddDeclRef(CombinerRecipe.LHS);
+        AddDeclRef(CombinerRecipe.RHS);
+        AddStmt(CombinerRecipe.Op);
+      }
     }
     return;
   }