msvc style bitfield packing (#7963)

Closes https://github.com/shader-slang/slang/issues/3646

New tests rather than just adding another TEST line to existing tests so
that we get the msvc- prefix in the output of slang-test

1 files changed, 36 insertions, 0 deletions

diff --git a/tests/language-feature/bitfield/repr.slang b/tests/language-feature/bitfield/repr.slang
new file mode 100644
index 000000000..a199b23ff
--- /dev/null
+++ b/tests/language-feature/bitfield/repr.slang
@@ -0,0 +1,36 @@
+//TEST(compute):COMPARE_COMPUTE(filecheck-buffer=CHECK):-cpu
+
+// Default GCC/Clang style packs from LSB to MSB
+// struct S { uint a:4; uint b:8; uint c:4; uint d:16; }
+// Memory layout (32-bit):
+// bits 0-3:   a (0x5)
+// bits 4-11:  b (0xAB) 
+// bits 12-15: c (0xC)
+// bits 16-31: d (0xDEF0)
+// Expected: 0xDEF0CAB5
+
+// CHECK: DEF0CAB5
+
+//TEST_INPUT:ubuffer(data=[0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<uint> outputBuffer;
+
+struct S {
+    uint a : 4;   // bits 0-3
+    uint b : 8;   // bits 4-11
+    uint c : 4;   // bits 12-15
+    uint d : 16;  // bits 16-31
+};
+
+[numthreads(1, 1, 1)]
+void computeMain()
+{
+    S s;
+    s.a = 0x5;
+    s.b = 0xAB;
+    s.c = 0xC;
+    s.d = 0xDEF0;
+
+    // Write the struct to memory and read it back as uint
+    outputBuffer[0] = *((uint*)&s);
+}
+