[clang] [HLSL] Define CBuffer field alignment for matrix types (PR #179836)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-hlsl

@llvm/pr-subscribers-clang

Author: Farzon Lotfi (farzonl)

<details>
<summary>Changes</summary>

fixes https://github.com/llvm/llvm-project/issues/179834

Change defines Matrix alignment as buffer row length (16). Same as arrays and structs.
Change also adds tests for matrix, matrix in structs, & arrays.

---
Full diff: https://github.com/llvm/llvm-project/pull/179836.diff


2 Files Affected:

- (modified) clang/lib/Sema/SemaHLSL.cpp (+2-2) 
- (added) clang/test/CodeGenHLSL/resources/cbuffer_matrix_align.hlsl (+71) 


``````````diff
diff --git a/clang/lib/Sema/SemaHLSL.cpp b/clang/lib/Sema/SemaHLSL.cpp
index 3e99a8f7d89d1..7dc8a4c7437e3 100644
--- a/clang/lib/Sema/SemaHLSL.cpp
+++ b/clang/lib/Sema/SemaHLSL.cpp
@@ -219,8 +219,8 @@ Decl *SemaHLSL::ActOnStartBuffer(Scope *BufferScope, bool CBuffer,
 
 static unsigned calculateLegacyCbufferFieldAlign(const ASTContext &Context,
                                                  QualType T) {
-  // Arrays and Structs are always aligned to new buffer rows
-  if (T->isArrayType() || T->isStructureType())
+  // Arrays, Matrices, and Structs are always aligned to new buffer rows
+  if (T->isArrayType() || T->isStructureType() || T->isConstantMatrixType())
     return 16;
 
   // Vectors are aligned to the type they contain
diff --git a/clang/test/CodeGenHLSL/resources/cbuffer_matrix_align.hlsl b/clang/test/CodeGenHLSL/resources/cbuffer_matrix_align.hlsl
new file mode 100644
index 0000000000000..ff4ce0f104f44
--- /dev/null
+++ b/clang/test/CodeGenHLSL/resources/cbuffer_matrix_align.hlsl
@@ -0,0 +1,71 @@
+// RUN: %clang_cc1 -std=hlsl202x -finclude-default-header -x hlsl -triple dxil-pc-shadermodel6.3-library %s -fnative-half-type -fsyntax-only -verify -verify-ignore-unexpected=warning
+
+cbuffer MatArr0Pass {
+  float2x4 A0p[2] : packoffset(c0.x);
+  float    a0tail : packoffset(c4.x);
+}
+
+cbuffer MatArr0Fail {
+  float2x4 A0f[2] : packoffset(c0.x);
+  float    a0bad  : packoffset(c1.w);
+  // expected-error at -1 {{packoffset overlap between 'a0bad', 'A0f'}}
+}
+
+// Struct containing a matrix.
+
+struct MS0 {
+  float2x4 M;
+  float2   V;
+};
+
+cbuffer MatStruct0Pass {
+  MS0   s0p   : packoffset(c0.x);
+  float s0tail: packoffset(c5.x);
+}
+
+cbuffer MatStruct0Fail {
+  MS0   s0f   : packoffset(c0.x);
+  float s0bad : packoffset(c0.y);
+  // expected-error at -1 {{packoffset overlap between 's0bad', 's0f'}}
+}
+
+// Nested struct containing a matrix.
+struct Inner0 {
+  float2x4 M;
+  float    F;
+};
+
+struct Outer0 {
+  float2   Head;
+  Inner0   I;
+  float2   Tail;
+};
+
+cbuffer MatNested0Pass {
+  Outer0 o0p   : packoffset(c0.x);
+  float  o0tail: packoffset(c8.x);
+}
+
+cbuffer MatNested0Fail {
+  Outer0 o0f  : packoffset(c0.x);
+  float  o0bad: packoffset(c3.y);
+  // expected-error at -1 {{packoffset overlap between 'o0bad', 'o0f'}}
+}
+
+// Array-of-struct where struct contains a matrix.
+
+struct AMS0 {
+  float2x4 M;
+  float2   V;
+};
+
+cbuffer MatArrStruct0Pass {
+  AMS0  as0p[2] : packoffset(c0.x);
+  float as0tail : packoffset(c10.x);
+}
+
+cbuffer MatArrStruct0Fail {
+  AMS0  as0f[2] : packoffset(c0.x);
+  float as0bad  : packoffset(c4.z);
+  // expected-error at -1 {{packoffset overlap between 'as0bad', 'as0f'}}
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/179836