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Fix a miscompile that occurs when reading a matrix contained in a struct with no sibling fields #8568

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748e030
Fix a miscompile that occurs when reading a matrix contained in a str…
aclysma Jun 19, 2026
d6a4e6b
clang format fix
aclysma Jun 19, 2026
1eefc31
Additional test per feedback https://github.com/microsoft/DirectXShad…
aclysma Jun 24, 2026
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35 changes: 24 additions & 11 deletions lib/HLSL/HLOperationLower.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -9222,14 +9222,21 @@ void TranslateStructBufMatSubscript(CallInst *CI, Value *handle,
assert(resultSize <= 16);
std::vector<Value *> idxList(resultSize);

// For raw buffers the byte offset rides in the buffer index and the element
// offset operand stays undef, so the per-element offset must accumulate into
// bufIdx. For structured buffers the per-element offset is the element offset
// and bufIdx is the structure index.
bool isRawBuf = DXIL::IsRawBuffer(ResKind);
Value *matBaseIdx = isRawBuf ? bufIdx : baseOffset;

switch (subOp) {
case HLSubscriptOpcode::ColMatSubscript:
case HLSubscriptOpcode::RowMatSubscript: {
for (unsigned i = 0; i < resultSize; i++) {
Value *offset =
CI->getArgOperand(HLOperandIndex::kMatSubscriptSubOpIdx + i);
offset = subBuilder.CreateMul(offset, EltByteSize);
idxList[i] = subBuilder.CreateAdd(baseOffset, offset);
idxList[i] = subBuilder.CreateAdd(matBaseIdx, offset);
}
} break;
case HLSubscriptOpcode::RowMatElement:
Expand All @@ -9238,7 +9245,7 @@ void TranslateStructBufMatSubscript(CallInst *CI, Value *handle,
for (unsigned i = 0; i < resultSize; i++) {
Value *offset =
subBuilder.CreateMul(EltIdxs->getAggregateElement(i), EltByteSize);
idxList[i] = subBuilder.CreateAdd(baseOffset, offset);
idxList[i] = subBuilder.CreateAdd(matBaseIdx, offset);
}
} break;
default:
Expand All @@ -9252,17 +9259,19 @@ void TranslateStructBufMatSubscript(CallInst *CI, Value *handle,
Value *subsUser = *(U++);
if (resultSize == 1) {
TranslateStructBufSubscriptUser(cast<Instruction>(subsUser), handle,
ResKind, bufIdx, idxList[0], status,
hlslOP, DL);
ResKind, isRawBuf ? idxList[0] : bufIdx,
isRawBuf ? baseOffset : idxList[0],
status, hlslOP, DL);
continue;
}
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(subsUser)) {
Value *GEPOffset = LowerGEPOnMatIndexListToIndex(GEP, idxList);

for (auto gepU = GEP->user_begin(); gepU != GEP->user_end();) {
Instruction *gepUserInst = cast<Instruction>(*(gepU++));
TranslateStructBufSubscriptUser(gepUserInst, handle, ResKind, bufIdx,
GEPOffset, status, hlslOP, DL);
TranslateStructBufSubscriptUser(
gepUserInst, handle, ResKind, isRawBuf ? GEPOffset : bufIdx,
isRawBuf ? baseOffset : GEPOffset, status, hlslOP, DL);
}

GEP->eraseFromParent();
Expand All @@ -9276,13 +9285,15 @@ void TranslateStructBufMatSubscript(CallInst *CI, Value *handle,
for (unsigned i = 0; i < resultSize; i++) {
Value *EltVal = stBuilder.CreateExtractElement(Val, i);
uint8_t mask = DXIL::kCompMask_X;
GenerateStructBufSt(handle, bufIdx, idxList[i], EltTy, hlslOP,
GenerateStructBufSt(handle, isRawBuf ? idxList[i] : bufIdx,
isRawBuf ? baseOffset : idxList[i], EltTy, hlslOP,
stBuilder, {EltVal, undefElt, undefElt, undefElt},
mask, alignment);
}
} else {
uint8_t mask = DXIL::kCompMask_X;
GenerateStructBufSt(handle, bufIdx, idxList[0], EltTy, hlslOP,
GenerateStructBufSt(handle, isRawBuf ? idxList[0] : bufIdx,
isRawBuf ? baseOffset : idxList[0], EltTy, hlslOP,
stBuilder, {Val, undefElt, undefElt, undefElt},
mask, alignment);
}
Expand All @@ -9300,14 +9311,16 @@ void TranslateStructBufMatSubscript(CallInst *CI, Value *handle,
for (unsigned i = 0; i < resultSize; i++) {
Value *ResultElt;
// TODO: This can be inefficient for row major matrix load
GenerateRawBufLd(handle, bufIdx, idxList[i],
GenerateRawBufLd(handle, isRawBuf ? idxList[i] : bufIdx,
isRawBuf ? baseOffset : idxList[i],
/*status*/ nullptr, EltTy, ResultElt, hlslOP,
ldBuilder, 1, alignment);
ldData = ldBuilder.CreateInsertElement(ldData, ResultElt, i);
}
} else {
GenerateRawBufLd(handle, bufIdx, idxList[0], /*status*/ nullptr, EltTy,
ldData, hlslOP, ldBuilder, 4, alignment);
GenerateRawBufLd(handle, isRawBuf ? idxList[0] : bufIdx,
isRawBuf ? baseOffset : idxList[0], /*status*/ nullptr,
EltTy, ldData, hlslOP, ldBuilder, 4, alignment);
}
ldUser->replaceAllUsesWith(ldData);
ldUser->eraseFromParent();
Expand Down
100 changes: 100 additions & 0 deletions tools/clang/test/CodeGenDXIL/hlsl/intrinsics/buffer-struct-matrix-load.ll
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Original file line number Diff line number Diff line change
@@ -0,0 +1,100 @@
; RUN: %dxopt %s -hlsl-passes-resume -dxilgen -S | FileCheck %s

target datalayout = "e-m:e-p:32:32-i1:32-i8:32-i16:32-i32:32-i64:64-f16:32-f32:32-f64:64-n8:16:32:64"
target triple = "dxil-ms-dx"

%struct.ByteAddressBuffer = type { i32 }
%struct.RWByteAddressBuffer = type { i32 }
%struct.Box = type { %class.matrix.float.4.4 }
%class.matrix.float.4.4 = type { [4 x <4 x float>] }
%dx.types.Handle = type { i8* }
%dx.types.ResourceProperties = type { i32, i32 }

@"\01?src@@3UByteAddressBuffer@@A" = external global %struct.ByteAddressBuffer, align 4
@"\01?dst@@3URWByteAddressBuffer@@A" = external global %struct.RWByteAddressBuffer, align 4

; Function Attrs: nounwind
define void @main() #0 {
%src = load %struct.ByteAddressBuffer, %struct.ByteAddressBuffer* @"\01?src@@3UByteAddressBuffer@@A"

; CHECK: [[HDL:%.*]] = call %dx.types.Handle @dx.op.createHandleForLib.struct.ByteAddressBuffer(i32 160, %struct.ByteAddressBuffer
; CHECK: [[ANHDL:%.*]] = call %dx.types.Handle @dx.op.annotateHandle(i32 216, %dx.types.Handle [[HDL]], %dx.types.ResourceProperties { i32 11, i32 0 })
; Column 0 of a column-major float4x4: elements at byte offsets 0, 4, 8, 12.
; The element-offset operand (4th arg) must be undef for raw-buffer loads.
; CHECK: @dx.op.rawBufferLoad.f32(i32 139, %dx.types.Handle [[ANHDL]], i32 0, i32 undef, i8 1, i32 4)
; CHECK: @dx.op.rawBufferLoad.f32(i32 139, %dx.types.Handle [[ANHDL]], i32 4, i32 undef, i8 1, i32 4)
; CHECK: @dx.op.rawBufferLoad.f32(i32 139, %dx.types.Handle [[ANHDL]], i32 8, i32 undef, i8 1, i32 4)
; CHECK: @dx.op.rawBufferLoad.f32(i32 139, %dx.types.Handle [[ANHDL]], i32 12, i32 undef, i8 1, i32 4)

%src.hdl = call %dx.types.Handle @"dx.hl.createhandle..%dx.types.Handle (i32, %struct.ByteAddressBuffer)"(i32 0, %struct.ByteAddressBuffer %src)
%src.ann = call %dx.types.Handle @"dx.hl.annotatehandle..%dx.types.Handle (i32, %dx.types.Handle, %dx.types.ResourceProperties, %struct.ByteAddressBuffer)"(i32 14, %dx.types.Handle %src.hdl, %dx.types.ResourceProperties { i32 11, i32 0 }, %struct.ByteAddressBuffer zeroinitializer)

; Load<Box>(0): returns a virtual pointer at raw-buffer byte offset 0.
%box.ptr = call %struct.Box* @"dx.hl.op.ro.%struct.Box* (i32, %dx.types.Handle, i32)"(i32 231, %dx.types.Handle %src.ann, i32 0)

; GEP to field 0 (the matrix m) inside Box -- byte offset within the struct = 0.
%mat.ptr = getelementptr inbounds %struct.Box, %struct.Box* %box.ptr, i32 0, i32 0

; ColMatSubscript (opcode 1): extract rows 0-3 of column 0 from the 4x4 matrix.
; Row indices 0-3 map to flat element indices 0-3 (column-major storage),
; i.e. byte offsets 0, 4, 8, 12 relative to the matrix base.
%col0.ptr = call <4 x float>* @"dx.hl.subscript.colMajor[].rn.<4 x float>* (i32, %class.matrix.float.4.4*, i32, i32, i32, i32)"(i32 1, %class.matrix.float.4.4* %mat.ptr, i32 0, i32 1, i32 2, i32 3)
%col0 = load <4 x float>, <4 x float>* %col0.ptr

; Write the result to a UAV so the loads have an observable use.
%dst = load %struct.RWByteAddressBuffer, %struct.RWByteAddressBuffer* @"\01?dst@@3URWByteAddressBuffer@@A"
%dst.hdl = call %dx.types.Handle @"dx.hl.createhandle..%dx.types.Handle (i32, %struct.RWByteAddressBuffer)"(i32 0, %struct.RWByteAddressBuffer %dst)
%dst.ann = call %dx.types.Handle @"dx.hl.annotatehandle..%dx.types.Handle (i32, %dx.types.Handle, %dx.types.ResourceProperties, %struct.RWByteAddressBuffer)"(i32 14, %dx.types.Handle %dst.hdl, %dx.types.ResourceProperties { i32 4107, i32 0 }, %struct.RWByteAddressBuffer zeroinitializer)
%col0.x = extractelement <4 x float> %col0, i32 0
%col0.y = extractelement <4 x float> %col0, i32 1
%col0.z = extractelement <4 x float> %col0, i32 2
%col0.w = extractelement <4 x float> %col0, i32 3
call void @"dx.hl.op..void (i32, %dx.types.Handle, i32, float)"(i32 277, %dx.types.Handle %dst.ann, i32 0, float %col0.x)
call void @"dx.hl.op..void (i32, %dx.types.Handle, i32, float)"(i32 277, %dx.types.Handle %dst.ann, i32 4, float %col0.y)
call void @"dx.hl.op..void (i32, %dx.types.Handle, i32, float)"(i32 277, %dx.types.Handle %dst.ann, i32 8, float %col0.z)
call void @"dx.hl.op..void (i32, %dx.types.Handle, i32, float)"(i32 277, %dx.types.Handle %dst.ann, i32 12, float %col0.w)

ret void
}

declare %dx.types.Handle @"dx.hl.createhandle..%dx.types.Handle (i32, %struct.ByteAddressBuffer)"(i32, %struct.ByteAddressBuffer) #1
declare %dx.types.Handle @"dx.hl.annotatehandle..%dx.types.Handle (i32, %dx.types.Handle, %dx.types.ResourceProperties, %struct.ByteAddressBuffer)"(i32, %dx.types.Handle, %dx.types.ResourceProperties, %struct.ByteAddressBuffer) #1
declare %struct.Box* @"dx.hl.op.ro.%struct.Box* (i32, %dx.types.Handle, i32)"(i32, %dx.types.Handle, i32) #2
declare <4 x float>* @"dx.hl.subscript.colMajor[].rn.<4 x float>* (i32, %class.matrix.float.4.4*, i32, i32, i32, i32)"(i32, %class.matrix.float.4.4*, i32, i32, i32, i32) #1
declare %dx.types.Handle @"dx.hl.createhandle..%dx.types.Handle (i32, %struct.RWByteAddressBuffer)"(i32, %struct.RWByteAddressBuffer) #1
declare %dx.types.Handle @"dx.hl.annotatehandle..%dx.types.Handle (i32, %dx.types.Handle, %dx.types.ResourceProperties, %struct.RWByteAddressBuffer)"(i32, %dx.types.Handle, %dx.types.ResourceProperties, %struct.RWByteAddressBuffer) #1
declare void @"dx.hl.op..void (i32, %dx.types.Handle, i32, float)"(i32, %dx.types.Handle, i32, float) #0

attributes #0 = { nounwind }
attributes #1 = { nounwind readnone }
attributes #2 = { nounwind readonly }

!pauseresume = !{!1}
!dx.version = !{!0}
!dx.valver = !{!2}
!dx.shaderModel = !{!3}
!dx.typeAnnotations = !{!4}
!dx.entryPoints = !{!8}
!dx.fnprops = !{!15}
!dx.options = !{!16, !17}

!0 = !{i32 1, i32 6}
!1 = !{!"hlsl-hlemit", !"hlsl-hlensure"}
!2 = !{i32 1, i32 9}
!3 = !{!"cs", i32 6, i32 6}
; dx.typeAnnotations: function annotations only (no user struct needed for this pass).
!4 = !{i32 1, void ()* @main, !5}
!5 = !{!6}
!6 = !{i32 1, !7, !7}
!7 = !{}
; dx.entryPoints: entry = main, no signatures, resources = {SRV=!10, UAV=!12}.
!8 = !{void ()* @main, !"main", null, !9, null}
!9 = !{!10, !12, null, null}
!10 = !{!11}
!11 = !{i32 0, %struct.ByteAddressBuffer* @"\01?src@@3UByteAddressBuffer@@A", !"src", i32 0, i32 0, i32 1, i32 11, i32 0, null}
!12 = !{!13}
!13 = !{i32 0, %struct.RWByteAddressBuffer* @"\01?dst@@3URWByteAddressBuffer@@A", !"dst", i32 0, i32 0, i32 1, i32 11, i1 false, i1 false, i1 false, null}
; dx.fnprops: CS kind=5, numthreads(1,1,1).
!15 = !{void ()* @main, i32 5, i32 1, i32 1, i32 1}
!16 = !{i32 64}
!17 = !{i32 -1}
31 changes: 31 additions & 0 deletions .../HLSLFileCheck/hlsl/objects/ByteAddressBuffer/bab_load_struct_matrix_element_offsets.hlsl
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Original file line number Diff line number Diff line change
@@ -0,0 +1,31 @@
// Reading individual matrix elements through the struct member of a
// ByteAddressBuffer.Load<struct{float4x4}> must address each element at its own
// byte offset. For raw buffers the byte offset rides in the load index operand
// and the element-offset operand stays undef, so the four first-column reads
// below must land at indices 0, 4, 8 and 12 -- they must not collapse to the
// matrix base (index 0), which is what happened before the matrix-element
// subscript path was taught the raw-buffer addressing convention.

// RUN: %dxc -T cs_6_6 -E cs %s | FileCheck %s

struct Box { float4x4 m; };

ByteAddressBuffer src : register(t0);
RWByteAddressBuffer dst : register(u0);

[numthreads(1, 1, 1)]
void cs()
{
Box b = src.Load<Box>(0);

// Column-major: _m00/_m10/_m20/_m30 live at bytes 0/4/8/12.
dst.Store(0, asuint(b.m._m00));
dst.Store(4, asuint(b.m._m10));
dst.Store(8, asuint(b.m._m20));
dst.Store(12, asuint(b.m._m30));
}

// CHECK: rawBufferLoad.f32(i32 139, %dx.types.Handle %{{.*}}, i32 0, i32 undef, i8 1, i32 4)
// CHECK: rawBufferLoad.f32(i32 139, %dx.types.Handle %{{.*}}, i32 4, i32 undef, i8 1, i32 4)
// CHECK: rawBufferLoad.f32(i32 139, %dx.types.Handle %{{.*}}, i32 8, i32 undef, i8 1, i32 4)
// CHECK: rawBufferLoad.f32(i32 139, %dx.types.Handle %{{.*}}, i32 12, i32 undef, i8 1, i32 4)
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