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[HLSL] Codegen for indexing of sub-arrays of multi-dimensional resource arrays #154248

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[HLSL] Codegen for indexing of sub-arrays of multi-dimensional resour…
hekota Aug 15, 2025
6469308
fix typo
hekota Aug 25, 2025
b4d0e69
code review feedback - update comments and tests
hekota Aug 29, 2025
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134 changes: 106 additions & 28 deletions clang/lib/CodeGen/CGHLSLRuntime.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,7 @@
#include "CodeGenModule.h"
#include "TargetInfo.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/Attrs.inc"
#include "clang/AST/Decl.h"
#include "clang/AST/RecursiveASTVisitor.h"
#include "clang/AST/Type.h"
Expand All @@ -36,6 +37,7 @@
#include "llvm/Support/Alignment.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/FormatVariadic.h"
#include <cstdint>

using namespace clang;
using namespace CodeGen;
Expand Down Expand Up @@ -190,6 +192,71 @@ static void createResourceCtorArgs(CodeGenModule &CGM, CXXConstructorDecl *CD,
Args.add(RValue::get(NameStr), AST.getPointerType(AST.CharTy.withConst()));
}

// Initializes local resource array variable. For multi-dimensional arrays it
// calls itself recursively to initialize its sub-arrays. The Index used in the
// resource constructor calls will begin at StartIndex and will be incremented
// for each array element. The last last used resource Index is returned to the
// caller.
static Value *initializeLocalResourceArray(
CodeGenFunction &CGF, AggValueSlot &ValueSlot,
const ConstantArrayType *ArrayTy, CXXConstructorDecl *CD,
llvm::Value *Range, llvm::Value *StartIndex, StringRef ResourceName,
HLSLResourceBindingAttr *RBA, HLSLVkBindingAttr *VkBinding,
ArrayRef<llvm::Value *> PrevGEPIndices, SourceLocation ArraySubsExprLoc) {

llvm::IntegerType *IntTy = CGF.CGM.IntTy;
llvm::Value *Index = StartIndex;
llvm::Value *One = llvm::ConstantInt::get(IntTy, 1);
uint64_t ArraySize = ArrayTy->getSExtSize();
QualType ElemType = ArrayTy->getElementType();
Address TmpArrayAddr = ValueSlot.getAddress();

// Add additional index to the getelementptr call indices.
// This index will be updated for each array element in the loops below.
SmallVector<llvm::Value *> GEPIndices(PrevGEPIndices);
GEPIndices.push_back(llvm::ConstantInt::get(IntTy, 0));

// array of arrays - recursively initialize the sub-arrays
if (ElemType->isArrayType()) {
const ConstantArrayType *SubArrayTy = cast<ConstantArrayType>(ElemType);
for (uint64_t I = 0; I < ArraySize; I++) {
if (I > 0) {
Index = CGF.Builder.CreateAdd(Index, One);
GEPIndices.back() = llvm::ConstantInt::get(IntTy, I);
}
// recursively initialize the sub-array
Index = initializeLocalResourceArray(
CGF, ValueSlot, SubArrayTy, CD, Range, Index, ResourceName, RBA,
VkBinding, GEPIndices, ArraySubsExprLoc);
}
return Index;
}

// array of resources - initialize each resource in the array
llvm::Type *Ty = CGF.ConvertTypeForMem(ElemType);
CharUnits ElemSize = CD->getASTContext().getTypeSizeInChars(ElemType);
CharUnits Align =
TmpArrayAddr.getAlignment().alignmentOfArrayElement(ElemSize);

for (uint64_t I = 0; I < ArraySize; I++) {
if (I > 0) {
Index = CGF.Builder.CreateAdd(Index, One);
GEPIndices.back() = llvm::ConstantInt::get(IntTy, I);
}
Address ThisAddress =
CGF.Builder.CreateGEP(TmpArrayAddr, GEPIndices, Ty, Align);
llvm::Value *ThisPtr = CGF.getAsNaturalPointerTo(ThisAddress, ElemType);

CallArgList Args;
createResourceCtorArgs(CGF.CGM, CD, ThisPtr, Range, Index, ResourceName,
RBA, VkBinding, Args);
CGF.EmitCXXConstructorCall(CD, Ctor_Complete, false, false, ThisAddress,
Args, ValueSlot.mayOverlap(), ArraySubsExprLoc,
ValueSlot.isSanitizerChecked());
}
return Index;
}

} // namespace

llvm::Type *
Expand Down Expand Up @@ -802,16 +869,14 @@ std::optional<LValue> CGHLSLRuntime::emitResourceArraySubscriptExpr(
ArraySubsExpr->getType()->isHLSLResourceRecordArray() &&
"expected resource array subscript expression");

// let clang codegen handle local resource array subscripts
const VarDecl *ArrayDecl = dyn_cast<VarDecl>(getArrayDecl(ArraySubsExpr));
// Let clang codegen handle local resource array subscripts,
// or when the subscript references on opaque expression (as part of
// ArrayInitLoopExpr AST node).
const VarDecl *ArrayDecl =
dyn_cast_or_null<VarDecl>(getArrayDecl(ArraySubsExpr));
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For learning purposes, when would the result of getArrayDecl ever be expected to be null? That seems weird to me in this case.

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@hekota hekota Aug 29, 2025 •
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It may happen when the ArraySubscriptExpr refers to an OpaqueValueExpr as part of an ArrayInitLoopExpr AST construct.

See https://godbolt.org/z/MzKsf8Kh5.

The ArrayInitLoopExpr AST node is used for array initialization from another array (see https://clang.llvm.org/doxygen/classclang_1_1ArrayInitLoopExpr.html#details) .

Notice how the first and the third ArraySubscriptExpr are the same (same pointer value)? We only do HLSL codegen on the first ArraySubscriptExpr where we create a local resource array with 2 elements. The second ArraySubscriptExpr is where getArrayDecl will be null because we hit the OpaqueValueExpr when looking for the decl. It will then be handled by Clang as a local array access on top of the local resource array that we created earlier.

if (!ArrayDecl || !ArrayDecl->hasGlobalStorage())
return std::nullopt;

if (ArraySubsExpr->getType()->isArrayType())
// FIXME: this is not yet implemented (llvm/llvm-project#145426)
llvm_unreachable(
"indexing of sub-arrays of multidimensional arrays not supported yet");

// get the resource array type
ASTContext &AST = ArrayDecl->getASTContext();
const Type *ResArrayTy = ArrayDecl->getType().getTypePtr();
Expand All @@ -832,26 +897,30 @@ std::optional<LValue> CGHLSLRuntime::emitResourceArraySubscriptExpr(
CGM.IntTy, AST.getConstantArrayElementCount(ArrayTy));
SubIndex = CGF.Builder.CreateMul(SubIndex, Multiplier);
}

Index = Index ? CGF.Builder.CreateAdd(Index, SubIndex) : SubIndex;
ASE = dyn_cast<ArraySubscriptExpr>(ASE->getBase()->IgnoreParenImpCasts());
}

// find binding info for the resource array (for implicit binding
// an HLSLResourceBindingAttr should have been added by SemaHLSL)
QualType ResourceTy = ArraySubsExpr->getType();
HLSLVkBindingAttr *VkBinding = ArrayDecl->getAttr<HLSLVkBindingAttr>();
HLSLResourceBindingAttr *RBA = ArrayDecl->getAttr<HLSLResourceBindingAttr>();
assert((VkBinding || RBA) && "resource array must have a binding attribute");

// Find the individual resource type
QualType ResultTy = ArraySubsExpr->getType();
QualType ResourceTy =
ResultTy->isArrayType() ? AST.getBaseElementType(ResultTy) : ResultTy;

// lookup the resource class constructor based on the resource type and
// binding
CXXConstructorDecl *CD = findResourceConstructorDecl(
AST, ResourceTy, VkBinding || RBA->hasRegisterSlot());

// create a temporary variable for the resource class instance (we need to
// create a temporary variable for the result, which is either going
// to be a single resource instance or a local array of resources (we need to
// return an LValue)
RawAddress TmpVar = CGF.CreateMemTemp(ResourceTy);
RawAddress TmpVar = CGF.CreateMemTemp(ResultTy);
if (CGF.EmitLifetimeStart(TmpVar.getPointer()))
CGF.pushFullExprCleanup<CodeGenFunction::CallLifetimeEnd>(
NormalEHLifetimeMarker, TmpVar);
Expand All @@ -860,26 +929,35 @@ std::optional<LValue> CGHLSLRuntime::emitResourceArraySubscriptExpr(
TmpVar, Qualifiers(), AggValueSlot::IsDestructed_t(true),
AggValueSlot::DoesNotNeedGCBarriers, AggValueSlot::IsAliased_t(false),
AggValueSlot::DoesNotOverlap);

Address ThisAddress = ValueSlot.getAddress();
llvm::Value *ThisPtr = CGF.getAsNaturalPointerTo(
ThisAddress, CD->getThisType()->getPointeeType());
Address TmpVarAddress = ValueSlot.getAddress();

// get total array size (= range size)
llvm::Value *Range =
llvm::ConstantInt::get(CGM.IntTy, getTotalArraySize(AST, ResArrayTy));

// assemble the constructor parameters
CallArgList Args;
createResourceCtorArgs(CGM, CD, ThisPtr, Range, Index, ArrayDecl->getName(),
RBA, VkBinding, Args);

// call the constructor
CGF.EmitCXXConstructorCall(CD, Ctor_Complete, false, false, ThisAddress, Args,
ValueSlot.mayOverlap(),
ArraySubsExpr->getExprLoc(),
ValueSlot.isSanitizerChecked());

return CGF.MakeAddrLValue(TmpVar, ArraySubsExpr->getType(),
AlignmentSource::Decl);
// if the result of the subscript operation is a single resource - call the
// constructor
if (ResultTy == ResourceTy) {
QualType ThisType = CD->getThisType()->getPointeeType();
llvm::Value *ThisPtr = CGF.getAsNaturalPointerTo(TmpVarAddress, ThisType);

// assemble the constructor parameters
CallArgList Args;
createResourceCtorArgs(CGM, CD, ThisPtr, Range, Index, ArrayDecl->getName(),
RBA, VkBinding, Args);
// call the constructor
CGF.EmitCXXConstructorCall(CD, Ctor_Complete, false, false, TmpVarAddress,
Args, ValueSlot.mayOverlap(),
ArraySubsExpr->getExprLoc(),
ValueSlot.isSanitizerChecked());
} else {
// result of the subscript operation is a local resource array
const ConstantArrayType *ArrayTy =
cast<ConstantArrayType>(ResultTy.getTypePtr());
initializeLocalResourceArray(CGF, ValueSlot, ArrayTy, CD, Range, Index,
ArrayDecl->getName(), RBA, VkBinding,
{llvm::ConstantInt::get(CGM.IntTy, 0)},
ArraySubsExpr->getExprLoc());
}
return CGF.MakeAddrLValue(TmpVar, ResultTy, AlignmentSource::Decl);
}
102 changes: 102 additions & 0 deletions clang/test/CodeGenHLSL/resources/res-array-global-subarray-many.hlsl
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@@ -0,0 +1,102 @@
// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.6-compute -finclude-default-header \
// RUN: -emit-llvm -disable-llvm-passes -o - %s | FileCheck %s

// CHECK: @[[BufA:.*]] = private unnamed_addr constant [2 x i8] c"A\00", align 1

RWBuffer<float> A[5][4][3][2] : register(u10, space2);
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minor nit: I think 'space2' is meaningless for this test?

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@hekota hekota Aug 29, 2025 •
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The value is passed into the constructor call.

RWStructuredBuffer<float> Out;

float foo(RWBuffer<float> Arr[3][2]) {
return Arr[1][0][0];
}

// NOTE:
// - _ZN4hlsl8RWBufferIfEC1EjjijPKc is the constructor call for explicit binding
// (has "jjij" in the mangled name) and the arguments are (register, space, range_size, index, name).
// - _ZN4hlsl8RWBufferIfEixEj is the subscript operator for RWBuffer<float>

// CHECK: define internal void @_Z4mainj(i32 noundef %GI)
// CHECK-NEXT: entry:
// CHECK-NEXT: %[[GI_alloca:.*]] = alloca i32, align 4
// CHECK-NEXT: %Sub = alloca [3 x [2 x %"class.hlsl::RWBuffer"]], align 4
// CHECK-NEXT: %[[Tmp0:.*]] = alloca [3 x [2 x %"class.hlsl::RWBuffer"]], align 4
// CHECK-NEXT: %a = alloca float, align 4
// CHECK-NEXT: %b = alloca float, align 4
// CHECK-NEXT: %[[Tmp1:.*]] = alloca [3 x [2 x %"class.hlsl::RWBuffer"]], align 4
// CHECK-NEXT: %[[Tmp2:.*]] = alloca [3 x [2 x %"class.hlsl::RWBuffer"]], align 4
// CHECK-NEXT: store i32 %GI, ptr %[[GI_alloca]], align 4
[numthreads(4,1,1)]
void main(uint GI : SV_GroupThreadID) {
// Codegen for "A[4][1]" - create local array [[Tmp0]] of size 3 x 2 and initialize
// each element by a call to the resource constructor
// The resource index for A[4][1][0][0] is 102 = 4 * (4 * 3 * 2) + 1 * (3 * 2)
// (index in the resource array as if it was flattened)
// CHECK-NEXT: %[[Ptr_Tmp0_0_0:.*]] = getelementptr [3 x [2 x %"class.hlsl::RWBuffer"]], ptr %tmp, i32 0, i32 0, i32 0
// CHECK-NEXT: call void @_ZN4hlsl8RWBufferIfEC1EjjijPKc(ptr {{.*}} %[[Ptr_Tmp0_0_0]], i32 noundef 10, i32 noundef 2, i32 noundef 120, i32 noundef 102, ptr noundef @A.str) #6
// CHECK-NEXT: %[[Ptr_Tmp0_0_1:.*]] = getelementptr [3 x [2 x %"class.hlsl::RWBuffer"]], ptr %tmp, i32 0, i32 0, i32 1
// CHECK-NEXT: call void @_ZN4hlsl8RWBufferIfEC1EjjijPKc(ptr {{.*}} %[[Ptr_Tmp0_0_1]], i32 noundef 10, i32 noundef 2, i32 noundef 120, i32 noundef 103, ptr noundef @A.str) #6
// CHECK-NEXT: %[[Ptr_Tmp0_1_0:.*]] = getelementptr [3 x [2 x %"class.hlsl::RWBuffer"]], ptr %tmp, i32 0, i32 1, i32 0
// CHECK-NEXT: call void @_ZN4hlsl8RWBufferIfEC1EjjijPKc(ptr {{.*}} %[[Ptr_Tmp0_1_0]], i32 noundef 10, i32 noundef 2, i32 noundef 120, i32 noundef 104, ptr noundef @A.str) #6
// CHECK-NEXT: %[[Ptr_Tmp0_1_1:.*]] = getelementptr [3 x [2 x %"class.hlsl::RWBuffer"]], ptr %tmp, i32 0, i32 1, i32 1
// CHECK-NEXT: call void @_ZN4hlsl8RWBufferIfEC1EjjijPKc(ptr {{.*}} %[[Ptr_Tmp0_1_1]], i32 noundef 10, i32 noundef 2, i32 noundef 120, i32 noundef 105, ptr noundef @A.str) #6
// CHECK-NEXT: %[[Ptr_Tmp0_2_0:.*]] = getelementptr [3 x [2 x %"class.hlsl::RWBuffer"]], ptr %tmp, i32 0, i32 2, i32 0
// CHECK-NEXT: call void @_ZN4hlsl8RWBufferIfEC1EjjijPKc(ptr {{.*}} %[[Ptr_Tmp0_2_0]], i32 noundef 10, i32 noundef 2, i32 noundef 120, i32 noundef 106, ptr noundef @A.str) #6
// CHECK-NEXT: %[[Ptr_Tmp0_2_1:.*]] = getelementptr [3 x [2 x %"class.hlsl::RWBuffer"]], ptr %tmp, i32 0, i32 2, i32 1
// CHECK-NEXT: call void @_ZN4hlsl8RWBufferIfEC1EjjijPKc(ptr {{.*}} %[[Ptr_Tmp0_2_1]], i32 noundef 10, i32 noundef 2, i32 noundef 120, i32 noundef 107, ptr noundef @A.str) #6
// After this Tmp0 values are copied to %Sub using the standard array loop initializaion
// (generated from ArrayInitLoopExpr AST node)
RWBuffer<float> Sub[3][2] = A[4][1];

// CHECK: %[[Ptr_Sub_2:.*]] = getelementptr inbounds [3 x [2 x %"class.hlsl::RWBuffer"]], ptr %Sub, i32 0, i32 2
// CHECK: %[[Ptr_Sub_2_1:.*]] = getelementptr inbounds [2 x %"class.hlsl::RWBuffer"], ptr %[[Ptr_Sub_2]], i32 0, i32 1
// CHECK-NEXT: %[[BufPtr:.*]] = call {{.*}} ptr @_ZN4hlsl8RWBufferIfEixEj(ptr {{.*}} %[[Ptr_Sub_2_1]], i32 noundef 0)
// CHECK-NEXT: %[[Sub_2_1_0_Value:.*]] = load float, ptr %[[BufPtr]], align 4
// CHECK-NEXT: store float %[[Sub_2_1_0_Value]], ptr %a, align 4
float a = Sub[2][1][0];

// Codegen for "foo(A[2][GI])" - create local array [[Tmp2]] of size 3 x 2 and initialize
// each element by a call to the resource constructor with dynamic index, and then
// copy-in the array as an argument of "foo"

// Calculate the resource index for A[2][GI][0][0] (index in the resource array as if it was flattened)
// The index is 2 * (4 * 3 * 2) + GI * (3 * 2) = 48 + GI * 6
// CHECK: %[[GI:.*]] = load i32, ptr %[[GI_alloca]], align 4
// CHECK-NEXT: %[[Index_A_2_GI_Tmp:.*]] = mul i32 %[[GI]], 6
// CHECK-NEXT: %[[Index_A_2_GI_0_0:.*]] = add i32 %[[Index_A_2_GI_Tmp]], 48

// A[2][GI][0][0]
// CHECK-NEXT: %[[Ptr_Tmp2_0_0:.*]] = getelementptr [3 x [2 x %"class.hlsl::RWBuffer"]], ptr %[[Tmp2]], i32 0, i32 0, i32 0
// CHECK-NEXT: call void @_ZN4hlsl8RWBufferIfEC1EjjijPKc(ptr {{.*}} %[[Ptr_Tmp2_0_0]], i32 noundef 10, i32 noundef 2, i32 noundef 120, i32 noundef %[[Index_A_2_GI_0_0]], ptr noundef @A.str)

// A[2][GI][0][1]
// CHECK-NEXT: %[[Index_A_2_GI_0_1:.*]] = add i32 %[[Index_A_2_GI_0_0]], 1
// CHECK-NEXT: %[[Ptr_Tmp2_0_1:.*]] = getelementptr [3 x [2 x %"class.hlsl::RWBuffer"]], ptr %[[Tmp2]], i32 0, i32 0, i32 1
// CHECK-NEXT: call void @_ZN4hlsl8RWBufferIfEC1EjjijPKc(ptr {{.*}} %[[Ptr_Tmp2_0_1]], i32 noundef 10, i32 noundef 2, i32 noundef 120, i32 noundef %[[Index_A_2_GI_0_1]], ptr noundef @A.str)

// A[2][GI][1][0]
// CHECK-NEXT: %[[Index_A_2_GI_1_0:.*]] = add i32 %[[Index_A_2_GI_0_1]], 1
// CHECK-NEXT: %[[Ptr_Tmp2_1_0:.*]] = getelementptr [3 x [2 x %"class.hlsl::RWBuffer"]], ptr %[[Tmp2]], i32 0, i32 1, i32 0
// CHECK-NEXT: call void @_ZN4hlsl8RWBufferIfEC1EjjijPKc(ptr {{.*}} %[[Ptr_Tmp2_1_0]], i32 noundef 10, i32 noundef 2, i32 noundef 120, i32 noundef %[[Index_A_2_GI_1_0]], ptr noundef @A.str)

// A[2][GI][1][1]
// CHECK-NEXT: %[[Index_A_2_GI_1_1:.*]] = add i32 %[[Index_A_2_GI_1_0]], 1
// CHECK-NEXT: %[[Ptr_Tmp2_1_1:.*]] = getelementptr [3 x [2 x %"class.hlsl::RWBuffer"]], ptr %[[Tmp2]], i32 0, i32 1, i32 1
// CHECK-NEXT: call void @_ZN4hlsl8RWBufferIfEC1EjjijPKc(ptr {{.*}} %[[Ptr_Tmp2_1_1]], i32 noundef 10, i32 noundef 2, i32 noundef 120, i32 noundef %[[Index_A_2_GI_1_1]], ptr noundef @A.str)

// A[2][GI][2][0]
// CHECK-NEXT: %[[Index_A_2_GI_2_0:.*]] = add i32 %[[Index_A_2_GI_1_1]], 1
// CHECK-NEXT: %[[Ptr_Tmp2_2_0:.*]] = getelementptr [3 x [2 x %"class.hlsl::RWBuffer"]], ptr %[[Tmp2]], i32 0, i32 2, i32 0
// CHECK-NEXT: call void @_ZN4hlsl8RWBufferIfEC1EjjijPKc(ptr {{.*}} %[[Ptr_Tmp2_2_0]], i32 noundef 10, i32 noundef 2, i32 noundef 120, i32 noundef %[[Index_A_2_GI_2_0]], ptr noundef @A.str)

// A[2][GI][2][1]
// CHECK-NEXT: %[[Index_A_2_GI_2_1:.*]] = add i32 %[[Index_A_2_GI_2_0]], 1
// CHECK-NEXT: %[[Ptr_Tmp2_2_1:.*]] = getelementptr [3 x [2 x %"class.hlsl::RWBuffer"]], ptr %[[Tmp2]], i32 0, i32 2, i32 1
// CHECK-NEXT: call void @_ZN4hlsl8RWBufferIfEC1EjjijPKc(ptr {{.*}} %[[Ptr_Tmp2_2_1]], i32 noundef 10, i32 noundef 2, i32 noundef 120, i32 noundef %[[Index_A_2_GI_2_1]], ptr noundef @A.str)

// CHECK-NEXT: call void @llvm.memcpy.p0.p0.i32(ptr align 4 %[[Tmp1]], ptr align 4 %[[Tmp2]], i32 24, i1 false)
// CHECK-NEXT: %[[FooReturned:.*]] = call {{.*}} float @_Z3fooA3_A2_N4hlsl8RWBufferIfEE(ptr noundef byval([3 x [2 x %"class.hlsl::RWBuffer"]]) align 4 %[[Tmp1]])
// CHECK-NEXT: store float %[[FooReturned]], ptr %b, align 4
float b = foo(A[2][GI]);

Out[0] = a + b;
}
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