Introduce CDataLayout & -fvk-use-c-layout (#8136)

Closes #8112. ~~The issue asks for a "C layout", but in this PR I use
the term "CPU layout" because this naming was pre-existing in the
codebase as `kCPULayoutRulesImpl_`. The primary purpose of this layout
is to match CPU-side struct definitions with the shader side. I'm open
to better naming suggestions, though.~~

Edit: switched back to using `CDataLayout` & `-fvk-use-c-layout`, as the
CPU target depends on the object layout rules of existing CPU layout
rules, but they're incompatible with actual shaders. So a new
`kCLayoutRulesImpl_` was needed anyway.

---------

Co-authored-by: Ellie Hermaszewska <ellieh@nvidia.com>

1 files changed, 57 insertions, 0 deletions

diff --git a/tests/spirv/c-layout-buffer.slang b/tests/spirv/c-layout-buffer.slang
new file mode 100644
index 000000000..c94d5402d
--- /dev/null
+++ b/tests/spirv/c-layout-buffer.slang
@@ -0,0 +1,57 @@
+//TEST(compute):COMPARE_COMPUTE_EX(filecheck-buffer=CHECK): -vk -emit-spirv-directly -compute
+//TEST:SIMPLE(filecheck=SPIRV): -stage compute -entry computeMain -target spirv -fvk-use-c-layout
+struct A
+{
+    uint64_t f0;
+    uint32_t f1;
+    // Padding of 4 bytes must exist in CPU layout, but not in scalar layout.
+};
+
+struct B
+{
+    float3 f;
+};
+
+struct C // Total size should be 40 bytes.
+{
+    A a;            // 16 bytes, alignment 8
+    uint32_t test1; // 4 bytes, alignment 4
+    B b;            // 12 bytes, alignment 4
+    uint32_t test2; // 4 bytes, alignment 4
+    bool c; // 1 bytes, alignment 1
+    bool d; // 1 bytes, alignment 1
+};
+
+//TEST_INPUT:set cpuBuffer = ubuffer(data=[1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20], stride=4)
+StructuredBuffer<C, CDataLayout> cpuBuffer;
+
+//TEST_INPUT:set outputBuffer = out ubuffer(data=[0 0 0 0], stride=4)
+RWStructuredBuffer<int> outputBuffer;
+
+[numthreads(1,1,1)]
+void computeMain()
+{
+    // The CPU layout should be the same as ScalarDataLayout, except that the
+    // size of structs is rounded up to their alignment.
+
+    // CHECK: 5
+    // CHECK: 9
+    // CHECK: F
+    // CHECK: 13
+    outputBuffer[0] = cpuBuffer[0].test1;
+    outputBuffer[1] = cpuBuffer[0].test2;
+    outputBuffer[2] = cpuBuffer[1].test1;
+    outputBuffer[3] = cpuBuffer[1].test2;
+}
+
+// SPIRV: OpMemberDecorate %A_c 0 Offset 0
+// SPIRV: OpMemberDecorate %A_c 1 Offset 8
+// SPIRV: OpMemberDecorate %B_c 0 Offset 0
+// SPIRV: OpMemberDecorate %C_c 0 Offset 0
+// SPIRV: OpMemberDecorate %C_c 1 Offset 16
+// SPIRV: OpMemberDecorate %C_c 2 Offset 20
+// SPIRV: OpMemberDecorate %C_c 3 Offset 32
+// SPIRV: OpMemberDecorate %C_c 4 Offset 36
+// SPIRV: OpMemberDecorate %C_c 5 Offset 37
+// SPIRV: OpDecorate %_runtimearr_C_c ArrayStride 40
+