[HLSL] Implement HLSL intialization list support

This PR implements HLSL's initialization list behvaior as specified in
the draft language specifcation under
[*Decl.Init.Agg*](https://microsoft.github.io/hlsl-specs/specs/hlsl.html
#Decl.Init.Agg).

This behavior is a bit unusual for C/C++ because intermediate braces in
initializer lists are ignored and a whole array of additional
conversions occur unintuitively to how initializaiton works in C.

The implementaiton in this PR generates a valid C/C++ initialization
list AST for the HLSL initializer so that there are no changes required
to Clang's CodeGen to support this. This design will also allow us to
use Clang's rewrite to convert HLSL initializers to valid C/C++
initializers that are equivalent. It does have the downside that it
will generate often redundant accesses during codegen. The IR optimizer
is extremely good at eliminating those so this will have no impact on
the final executable performance.

There is some opportunity for optimizing the initializer list
generation that we could consider in subsequent commits. One notable
opportunity would be to identify aggregate objects that occur in the
same place in both initializers and do not require converison, those
aggregates could be initialized as aggregates rather than fully
scalarized.

Closes #56067

Author: llvm-beanz

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -12574,6 +12574,9 @@ def err_hlsl_pointers_unsupported : Error<
   "%select{pointers|references}0 are unsupported in HLSL">;
 def err_hlsl_missing_resource_class : Error<"HLSL resource needs to have [[hlsl::resource_class()]] attribute">;
 def err_hlsl_attribute_needs_intangible_type: Error<"attribute %0 can be used only on HLSL intangible type %1">;
+def err_hlsl_incorrect_num_initializers: Error<
+  "too %select{few|many}0 initializers in list for type %1 "
+  "(expected %2 but found %3)">;
 
 def err_hlsl_operator_unsupported : Error<
   "the '%select{&|*|->}0' operator is unsupported in HLSL">;

clang/include/clang/Sema/SemaHLSL.h

@@ -26,6 +26,8 @@
 namespace clang {
 class AttributeCommonInfo;
 class IdentifierInfo;
+class InitializedEntity;
+class InitializationKind;
 class ParsedAttr;
 class Scope;
 class VarDecl;
@@ -145,6 +147,9 @@ class SemaHLSL : public SemaBase {
 
   QualType getInoutParameterType(QualType Ty);
 
+  bool TransformInitList(const InitializedEntity &Entity,
+                         const InitializationKind &Kind, InitListExpr *Init);
+
 private:
   // HLSL resource type attributes need to be processed all at once.
   // This is a list to collect them.

clang/lib/Sema/SemaChecking.cpp

@@ -11625,9 +11625,12 @@ static void AnalyzeImplicitConversions(
 
   // Propagate whether we are in a C++ list initialization expression.
   // If so, we do not issue warnings for implicit int-float conversion
-  // precision loss, because C++11 narrowing already handles it.
-  bool IsListInit = Item.IsListInit ||
-                    (isa<InitListExpr>(OrigE) && S.getLangOpts().CPlusPlus);
+  // precision loss, because C++11 narrowing already handles it. HLSL's
+  // initialization lists are special, so they shouldn't observe the C++
+  // behavior here.
+  bool IsListInit =
+      Item.IsListInit || (isa<InitListExpr>(OrigE) &&
+                          S.getLangOpts().CPlusPlus && !S.getLangOpts().HLSL);
 
   if (E->isTypeDependent() || E->isValueDependent())
     return;

clang/lib/Sema/SemaHLSL.cpp

@@ -2576,3 +2576,162 @@ void SemaHLSL::processExplicitBindingsOnDecl(VarDecl *VD) {
     }
   }
 }
+
+static bool CastInitializer(Sema &S, ASTContext &Ctx, Expr *E,
+                            llvm::SmallVectorImpl<Expr *> &List,
+                            llvm::SmallVectorImpl<QualType> &DestTypes) {
+  if (List.size() >= DestTypes.size())
+    return false;
+  InitializedEntity Entity =
+      InitializedEntity::InitializeParameter(Ctx, DestTypes[List.size()], false);
+  ExprResult Res =
+      S.PerformCopyInitialization(Entity, E->getBeginLoc(), E);
+  if (Res.isInvalid())
+    return false;
+  Expr *Init = Res.get();
+  List.push_back(Init);
+  return true;
+}
+
+static void BuildIntializerList(Sema &S, ASTContext &Ctx, Expr *E,
+                                llvm::SmallVectorImpl<Expr *> &List,
+                                llvm::SmallVectorImpl<QualType> &DestTypes,
+                                bool &ExcessInits) {
+  if (List.size() >= DestTypes.size()) {
+    ExcessInits = true;
+    return;
+  }
+
+  // If this is an initialization list, traverse the sub initializers.
+  if (auto *Init = dyn_cast<InitListExpr>(E)) {
+    for (auto *SubInit : Init->inits())
+      BuildIntializerList(S, Ctx, SubInit, List, DestTypes, ExcessInits);
+    return;
+  }
+
+  // If this is a scalar type, just enqueue the expression.
+  QualType Ty = E->getType();
+  if (Ty->isScalarType()) {
+    (void)CastInitializer(S, Ctx, E, List, DestTypes);
+    return;
+  }
+
+  if (auto *ATy = Ty->getAs<VectorType>()) {
+    uint64_t Size = ATy->getNumElements();
+
+    if (List.size() + Size > DestTypes.size()) {
+      ExcessInits = true;
+      return;
+    }
+    QualType SizeTy = Ctx.getSizeType();
+    uint64_t SizeTySize = Ctx.getTypeSize(SizeTy);
+    for (uint64_t I = 0; I < Size; ++I) {
+      auto *Idx = IntegerLiteral::Create(Ctx, llvm::APInt(SizeTySize, I),
+                                         SizeTy, SourceLocation());
+
+      ExprResult ElExpr = S.CreateBuiltinArraySubscriptExpr(
+          E, E->getBeginLoc(), Idx, E->getEndLoc());
+      if (ElExpr.isInvalid())
+        return;
+      if (!CastInitializer(S, Ctx, ElExpr.get(), List, DestTypes))
+        return;
+    }
+    return;
+  }
+
+  if (auto *VTy = dyn_cast<ConstantArrayType>(Ty.getTypePtr())) {
+    uint64_t Size = VTy->getZExtSize();
+    QualType SizeTy = Ctx.getSizeType();
+    uint64_t SizeTySize = Ctx.getTypeSize(SizeTy);
+    for (uint64_t I = 0; I < Size; ++I) {
+      auto *Idx = IntegerLiteral::Create(Ctx, llvm::APInt(SizeTySize, I),
+                                         SizeTy, SourceLocation());
+      ExprResult ElExpr = S.CreateBuiltinArraySubscriptExpr(
+          E, E->getBeginLoc(), Idx, E->getEndLoc());
+      if (ElExpr.isInvalid())
+        return;
+      BuildIntializerList(S, Ctx, ElExpr.get(), List, DestTypes, ExcessInits);
+    }
+    return;
+  }
+
+  if (auto *RTy = Ty->getAs<RecordType>()) {
+    for (auto *FD : RTy->getDecl()->fields()) {
+      DeclAccessPair Found = DeclAccessPair::make(FD, FD->getAccess());
+      DeclarationNameInfo NameInfo(FD->getDeclName(), E->getBeginLoc());
+      ExprResult Res = S.BuildFieldReferenceExpr(
+          E, false, E->getBeginLoc(), CXXScopeSpec(), FD, Found, NameInfo);
+      if (Res.isInvalid())
+        return;
+      BuildIntializerList(S, Ctx, Res.get(), List, DestTypes, ExcessInits);
+    }
+  }
+}
+
+static Expr *GenerateInitLists(ASTContext &Ctx, QualType Ty,
+                               llvm::SmallVectorImpl<Expr *>::iterator &It) {
+  if (Ty->isScalarType()) {
+    return *(It++);
+  }
+  llvm::SmallVector<Expr *> Inits;
+  assert(!isa<MatrixType>(Ty) && "Matrix types not yet supported in HLSL");
+  if (Ty->isVectorType() || Ty->isConstantArrayType()) {
+    QualType ElTy;
+    uint64_t Size = 0;
+    if (auto *ATy = Ty->getAs<VectorType>()) {
+      ElTy = ATy->getElementType();
+      Size = ATy->getNumElements();
+    } else {
+      auto *VTy = cast<ConstantArrayType>(Ty.getTypePtr());
+      ElTy = VTy->getElementType();
+      Size = VTy->getZExtSize();
+    }
+    for (uint64_t I = 0; I < Size; ++I)
+      Inits.push_back(GenerateInitLists(Ctx, ElTy, It));
+  }
+  if (const RecordDecl *RD = Ty->getAsRecordDecl()) {
+    for (auto *FD : RD->fields()) {
+      Inits.push_back(GenerateInitLists(Ctx, FD->getType(), It));
+    }
+  }
+  auto *NewInit = new (Ctx) InitListExpr(Ctx, Inits.front()->getBeginLoc(),
+                                         Inits, Inits.back()->getEndLoc());
+  NewInit->setType(Ty);
+  return NewInit;
+}
+
+bool SemaHLSL::TransformInitList(const InitializedEntity &Entity,
+                                 const InitializationKind &Kind,
+                                 InitListExpr *Init) {
+  // If the initializer is a scalar, just return it.
+  if (Init->getType()->isScalarType())
+    return true;
+  ASTContext &Ctx = SemaRef.getASTContext();
+  llvm::SmallVector<QualType, 16> DestTypes;
+  // An initializer list might be attempting to initialize a reference or
+  // rvalue-reference. When checking the initializer we should look through the
+  // reference.
+  QualType InitTy = Entity.getType().getNonReferenceType();
+  BuildFlattenedTypeList(InitTy, DestTypes);
+
+  llvm::SmallVector<Expr *, 16> ArgExprs;
+  bool ExcessInits = false;
+  for (Expr *Arg : Init->inits())
+    BuildIntializerList(SemaRef, Ctx, Arg, ArgExprs, DestTypes, ExcessInits);
+
+  if (DestTypes.size() != ArgExprs.size() || ExcessInits) {
+    int TooManyOrFew = ExcessInits ? 1 : 0;
+    SemaRef.Diag(Init->getBeginLoc(), diag::err_hlsl_incorrect_num_initializers)
+        << TooManyOrFew << InitTy << DestTypes.size() << ArgExprs.size();
+    return false;
+  }
+
+  auto It = ArgExprs.begin();
+  // GenerateInitLists will always return an InitListExpr here, because the
+  // scalar case is handled above.
+  auto *NewInit = cast<InitListExpr>(GenerateInitLists(Ctx, InitTy, It));
+  Init->resizeInits(Ctx, NewInit->getNumInits());
+  for (unsigned I = 0; I < NewInit->getNumInits(); ++I)
+    Init->updateInit(Ctx, I, NewInit->getInit(I));
+  return true;
+}

clang/lib/Sema/SemaInit.cpp

@@ -26,6 +26,7 @@
 #include "clang/Sema/Initialization.h"
 #include "clang/Sema/Lookup.h"
 #include "clang/Sema/Ownership.h"
+#include "clang/Sema/SemaHLSL.h"
 #include "clang/Sema/SemaObjC.h"
 #include "llvm/ADT/APInt.h"
 #include "llvm/ADT/FoldingSet.h"
@@ -4783,6 +4784,10 @@ static void TryListInitialization(Sema &S,
                                   bool TreatUnavailableAsInvalid) {
   QualType DestType = Entity.getType();
 
+  if (S.getLangOpts().HLSL &&
+      !S.HLSL().TransformInitList(Entity, Kind, InitList))
+    return;
+
   // C++ doesn't allow scalar initialization with more than one argument.
   // But C99 complex numbers are scalars and it makes sense there.
   if (S.getLangOpts().CPlusPlus && DestType->isScalarType() &&

clang/test/CodeGenHLSL/ArrayTemporary.hlsl

@@ -1,3 +1,4 @@
+
 // RUN: %clang_cc1 -triple dxil-pc-shadermodel6.3-library -emit-llvm -disable-llvm-passes -o - %s | FileCheck %s
 
 void fn(float x[2]) { }
@@ -27,7 +28,7 @@ void fn2(Obj O[4]) { }
 // CHECK: call void @llvm.memcpy.p0.p0.i32(ptr align 4 [[Tmp]], ptr align 4 [[Arr]], i32 32, i1 false)
 // CHECK: call void {{.*}}fn2{{.*}}(ptr noundef byval([4 x %struct.Obj]) align 4 [[Tmp]])
 void call2() {
-  Obj Arr[4] = {};
+  Obj Arr[4] = {{0, 0}, {0, 0}, {0, 0}, {0, 0}};
   fn2(Arr);
 }