[spirv] Emit warning for packoffset (#951)

We do not support packoffset right now. Emit warning and ignore it.

docs/SPIR-V.rst

@@ -2348,4 +2348,8 @@ either because of no Vulkan equivalents at the moment, or because of deprecation
   only allowed to be applied to members of structures. A warning will be issued by the compiler.
 * The Hull shader ``partitioning`` attribute may not have the ``pow2`` value. The compiler
   will emit an error. Other attribute values are supported and described in the
-  `Hull Entry Point Attributes`_ section.
+  `Hull Entry Point Attributes`_ section.
+* ``cbuffer``/``tbuffer`` member initializer: no Vulkan equivalent. The compiler
+  will emit an warning and ignore it.
+* ``:packoffset()``: Not supported right now. The compiler will emit an warning
+  and ignore it.

tools/clang/lib/SPIRV/SPIRVEmitter.cpp

@@ -883,12 +883,17 @@ void SPIRVEmitter::doHLSLBufferDecl(const HLSLBufferDecl *bufferDecl) {
   // Check and emit warnings for member intializers which are not
   // supported in Vulkan
   for (const auto *member : bufferDecl->decls()) {
-    if (const auto *varMember = dyn_cast<VarDecl>(member))
+    if (const auto *varMember = dyn_cast<VarDecl>(member)) {
       if (const auto *init = varMember->getInit())
         emitWarning("%select{tbuffer|cbuffer}0 member initializer "
                     "ignored since no equivalent in Vulkan",
                     init->getExprLoc())
             << bufferDecl->isCBuffer() << init->getSourceRange();
+
+      for (const auto *annotation : varMember->getUnusualAnnotations())
+        if (const auto *packing = dyn_cast<hlsl::ConstantPacking>(annotation))
+          emitWarning("packoffset ignored since not supported", packing->Loc);
+    }
   }
   validateVKAttributes(bufferDecl);
   (void)declIdMapper.createCTBuffer(bufferDecl);

tools/clang/test/CodeGenSPIRV/vk.layout.cbuffer.packoffset.hlsl

@@ -0,0 +1,14 @@
+// Run: %dxc -T vs_6_0 -E main
+
+cbuffer MyCBuffer {
+    float4 data1;
+    float4 data2 : packoffset(c1);
+    float  data3 : packoffset(c2.y);
+}
+
+float4 main() : A {
+    return data1 + data2 + data3;
+}
+
+// CHECK: :5:20: warning: packoffset ignored since not supported
+// CHECK: :6:20: warning: packoffset ignored since not supported

tools/clang/unittests/SPIRV/CodeGenSPIRVTest.cpp

@@ -1091,6 +1091,10 @@ TEST_F(FileTest, VulkanLayoutPushConstantStd430) {
   runFileTest("vk.layout.push-constant.std430.hlsl");
 }
 
+TEST_F(FileTest, VulkanLayoutCBufferPackOffset) {
+  runFileTest("vk.layout.cbuffer.packoffset.hlsl", Expect::Warning);
+}
+
 // HS: for different Patch Constant Functions
 TEST_F(FileTest, HullShaderPCFVoid) { runFileTest("hs.pcf.void.hlsl"); }
 TEST_F(FileTest, HullShaderPCFTakesInputPatch) {