https://github.com/V-FEXrt created
https://github.com/llvm/llvm-project/pull/128086
Fixes #119641
Update SemaHLSL to correctly calculate the alignment barrier for scalars that
are not 4 bytes wide
>From bebfc20fac6b27d02bca9af328d0568018672c71 Mon Sep 17 00:00:00 2001
From: Ashley Coleman <ascole...@microsoft.com>
Date: Thu, 20 Feb 2025 16:16:16 -0700
Subject: [PATCH 1/2] [hlsl][Sema] Fix Struct Size Calculation containing 16
and 32 bit wide scalars
---
clang/lib/Sema/SemaHLSL.cpp | 26 ++++++++--
clang/test/CodeGenHLSL/cbuffer_align.hlsl | 60 +++++++++++++++++++++++
2 files changed, 81 insertions(+), 5 deletions(-)
create mode 100644 clang/test/CodeGenHLSL/cbuffer_align.hlsl
diff --git a/clang/lib/Sema/SemaHLSL.cpp b/clang/lib/Sema/SemaHLSL.cpp
index d26d85d5861b1..6f99b7899891d 100644
--- a/clang/lib/Sema/SemaHLSL.cpp
+++ b/clang/lib/Sema/SemaHLSL.cpp
@@ -172,6 +172,26 @@ Decl *SemaHLSL::ActOnStartBuffer(Scope *BufferScope, bool
CBuffer,
return Result;
}
+static unsigned calculateLegacyCbufferFieldAlign(const ASTContext &Context,
+ QualType T) {
+ // Aggregate types are always aligned to new buffer rows
+ if (T->isAggregateType())
+ return 16;
+
+ assert(Context.getTypeSize(T) <= 64 && "Scalar bit widths larger than 64 not
supported");
+
+ // 64 bit types such as double and uint64_t align to 8 bytes
+ if (Context.getTypeSize(T) == 64)
+ return 8;
+
+ // Half types align to 2 bytes only if native half is available
+ if (T->isHalfType() && Context.getLangOpts().NativeHalfType)
+ return 2;
+
+ // Everything else aligns to 4 bytes
+ return 4;
+}
+
// Calculate the size of a legacy cbuffer type in bytes based on
//
https://learn.microsoft.com/en-us/windows/win32/direct3dhlsl/dx-graphics-hlsl-packing-rules
static unsigned calculateLegacyCbufferSize(const ASTContext &Context,
@@ -183,11 +203,7 @@ static unsigned calculateLegacyCbufferSize(const
ASTContext &Context,
for (const FieldDecl *Field : RD->fields()) {
QualType Ty = Field->getType();
unsigned FieldSize = calculateLegacyCbufferSize(Context, Ty);
- // FIXME: This is not the correct alignment, it does not work for 16-bit
- // types. See llvm/llvm-project#119641.
- unsigned FieldAlign = 4;
- if (Ty->isAggregateType())
- FieldAlign = CBufferAlign;
+ unsigned FieldAlign = calculateLegacyCbufferFieldAlign(Context, Ty);
Size = llvm::alignTo(Size, FieldAlign);
Size += FieldSize;
}
diff --git a/clang/test/CodeGenHLSL/cbuffer_align.hlsl
b/clang/test/CodeGenHLSL/cbuffer_align.hlsl
new file mode 100644
index 0000000000000..31db2e0726020
--- /dev/null
+++ b/clang/test/CodeGenHLSL/cbuffer_align.hlsl
@@ -0,0 +1,60 @@
+// RUN: %clang_cc1 -std=hlsl2021 -finclude-default-header -x hlsl -triple \
+// RUN: dxil-pc-shadermodel6.3-library %s -fnative-half-type \
+// RUN: -emit-llvm -disable-llvm-passes -o - | FileCheck %s
--check-prefix=CHECK-HALF
+
+// RUN: %clang_cc1 -std=hlsl2021 -finclude-default-header -x hlsl -triple \
+// RUN: dxil-pc-shadermodel6.3-library %s \
+// RUN: -emit-llvm -disable-llvm-passes -o - | FileCheck %s
--check-prefix=CHECK-FLOAT
+
+
+struct S1 {
+ half a; // 2 bytes + 2 bytes pad or 4 bytes
+ float b; // 4 bytes
+ half c; // 2 bytes + 2 bytes pad or 4 bytes
+ float d; // 4 bytes
+ double e; // 8 bytes
+};
+
+struct S2 {
+ half a; // 2 bytes or 4 bytes
+ half b; // 2 bytes or 4 bytes
+ float e; // 4 bytes or 4 bytes + 4 padding
+ double f; // 8 bytes
+};
+
+struct S3 {
+ half a; // 2 bytes + 6 bytes pad or 4 bytes + 4 bytes pad
+ uint64_t b; // 8 bytes
+};
+
+struct S4 {
+ float a; // 4 bytes
+ half b; // 2 bytes or 4 bytes
+ half c; // 2 bytes or 4 bytes + 4 bytes pad
+ double d; // 8 bytes
+};
+
+
+cbuffer CB0 {
+ // CHECK-HALF: @CB0.cb = external constant target("dx.CBuffer",
target("dx.Layout", %__cblayout_CB0, 24, 0))
+ // CHECK-FLOAT: @CB0.cb = external constant target("dx.CBuffer",
target("dx.Layout", %__cblayout_CB0, 24, 0))
+ S1 s1;
+}
+
+cbuffer CB1 {
+ // CHECK-HALF: @CB1.cb = external constant target("dx.CBuffer",
target("dx.Layout", %__cblayout_CB1, 16, 0))
+ // CHECK-FLOAT: @CB1.cb = external constant target("dx.CBuffer",
target("dx.Layout", %__cblayout_CB1, 24, 0))
+ S2 s2;
+}
+
+cbuffer CB2 {
+ // CHECK-HALF: @CB2.cb = external constant target("dx.CBuffer",
target("dx.Layout", %__cblayout_CB2, 16, 0))
+ // CHECK-FLOAT: @CB2.cb = external constant target("dx.CBuffer",
target("dx.Layout", %__cblayout_CB2, 16, 0))
+ S3 s3;
+}
+
+cbuffer CB3 {
+ // CHECK-HALF: @CB3.cb = external constant target("dx.CBuffer",
target("dx.Layout", %__cblayout_CB3, 16, 0))
+ // CHECK-FLOAT: @CB3.cb = external constant target("dx.CBuffer",
target("dx.Layout", %__cblayout_CB3, 24, 0))
+ S4 s4;
+}
>From e8b3032cbf09e2e3170a212b35ac0ad2f755ca9f Mon Sep 17 00:00:00 2001
From: Ashley Coleman <ascole...@microsoft.com>
Date: Thu, 20 Feb 2025 16:16:47 -0700
Subject: [PATCH 2/2] format
---
clang/lib/Sema/SemaHLSL.cpp | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/clang/lib/Sema/SemaHLSL.cpp b/clang/lib/Sema/SemaHLSL.cpp
index 6f99b7899891d..cccfd4aec7eb2 100644
--- a/clang/lib/Sema/SemaHLSL.cpp
+++ b/clang/lib/Sema/SemaHLSL.cpp
@@ -173,12 +173,13 @@ Decl *SemaHLSL::ActOnStartBuffer(Scope *BufferScope, bool
CBuffer,
}
static unsigned calculateLegacyCbufferFieldAlign(const ASTContext &Context,
- QualType T) {
+ QualType T) {
// Aggregate types are always aligned to new buffer rows
if (T->isAggregateType())
return 16;
- assert(Context.getTypeSize(T) <= 64 && "Scalar bit widths larger than 64 not
supported");
+ assert(Context.getTypeSize(T) <= 64 &&
+ "Scalar bit widths larger than 64 not supported");
// 64 bit types such as double and uint64_t align to 8 bytes
if (Context.getTypeSize(T) == 64)
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