[SPIR-V] Allow SubpassInput without InputAttachmentIndex (#6240)

Vulkan allows SubpassInputs without an input attachment index specified,
so the error when it is missing has been removed and tests have been
updated.

As far as I can tell, there aren't earlier Vulkan or SPIR-V versions
where the presence of the the input attachment index was explicitly
required, so allowing it to be omitted in all cases.

Also added a test to verify that this fixes #2808 at the same time.

Fixes #6238, #2808

docs/SPIR-V.rst

@@ -213,8 +213,10 @@ For example:
 
   [[vk::input_attachment_index(i)]] SubpassInput input;
 
-An ``vk::input_attachment_index`` of ``i`` selects the ith entry in the input
-pass list. (See Vulkan API spec for more information.)
+A ``vk::input_attachment_index`` of ``i`` selects the ith entry in the input
+pass list. A subpass input without a ``vk::input_attachment_index`` will be
+associated with the depth/stencil attachment. (See Vulkan API spec for more
+information.)
 
 Push constants
 ~~~~~~~~~~~~~~

tools/clang/lib/SPIRV/SpirvEmitter.cpp

@@ -1560,16 +1560,6 @@ void SpirvEmitter::doFunctionDecl(const FunctionDecl *decl) {
 bool SpirvEmitter::validateVKAttributes(const NamedDecl *decl) {
   bool success = true;
 
-  if (const auto *varDecl = dyn_cast<VarDecl>(decl)) {
-    const auto varType = varDecl->getType();
-    if ((isSubpassInput(varType) || isSubpassInputMS(varType)) &&
-        !varDecl->hasAttr<VKInputAttachmentIndexAttr>()) {
-      emitError("missing vk::input_attachment_index attribute",
-                varDecl->getLocation());
-      success = false;
-    }
-  }
-
   if (decl->getAttr<VKInputAttachmentIndexAttr>()) {
     if (!decl->isExternallyVisible()) {
       emitError("SubpassInput(MS) must be externally visible",

tools/clang/test/CodeGenSPIRV/vk.subpass-input.binding.hlsl

@@ -4,6 +4,8 @@
 // CHECK: OpDecorate %SI1 InputAttachmentIndex 1
 // CHECK: OpDecorate %SI2 InputAttachmentIndex 2
 
+// CHECK-NOT: OpDecorate %SI3 InputAttachmentIndex
+
 // CHECK: OpDecorate %SI1 DescriptorSet 0
 // CHECK: OpDecorate %SI1 Binding 5
 
@@ -13,6 +15,9 @@
 // CHECK: OpDecorate %SI0 DescriptorSet 0
 // CHECK: OpDecorate %SI0 Binding 0
 
+// CHECK: OpDecorate %SI3 DescriptorSet 0
+// CHECK: OpDecorate %SI3 Binding 1
+
 [[vk::input_attachment_index(0)]]
 SubpassInput SI0;
 
@@ -22,6 +27,8 @@ SubpassInput SI1;
 [[vk::input_attachment_index(2), vk::binding(5, 3)]]
 SubpassInput SI2;
 
+SubpassInput SI3;
+
 void main() {
 
 }

tools/clang/test/CodeGenSPIRV/vk.subpass-input.hlsl

@@ -22,24 +22,28 @@
 // CHECK: %type_subpass_image_4 = OpTypeImage %int SubpassData 2 0 1 2 Unknown
 // CHECK: %_ptr_UniformConstant_type_subpass_image_4 = OpTypePointer UniformConstant %type_subpass_image_4
 
-// CHCK:   %SI_f4 = OpVariable %_ptr_UniformConstant_type_subpass_image UniformConstant
+// CHECK:   %SI_f4 = OpVariable %_ptr_UniformConstant_type_subpass_image UniformConstant
 [[vk::input_attachment_index(0)]]  SubpassInput           SI_f4;
-// CHCK:   %SI_i3 = OpVariable %_ptr_UniformConstant_type_subpass_image_0 UniformConstant
+// CHECK:   %SI_i3 = OpVariable %_ptr_UniformConstant_type_subpass_image_0 UniformConstant
 [[vk::input_attachment_index(1)]]  SubpassInput<int3>     SI_i3;
-// CHCK:   %SI_u2 = OpVariable %_ptr_UniformConstant_type_subpass_image_1 UniformConstant
+// CHECK:   %SI_u2 = OpVariable %_ptr_UniformConstant_type_subpass_image_1 UniformConstant
 [[vk::input_attachment_index(2)]]  SubpassInput<uint2>    SI_u2;
-// CHCK:   %SI_f1 = OpVariable %_ptr_UniformConstant_type_subpass_image UniformConstant
+// CHECK:   %SI_f1 = OpVariable %_ptr_UniformConstant_type_subpass_image UniformConstant
 [[vk::input_attachment_index(3)]]  SubpassInput<float>    SI_f1;
 
-// CHCK: %SIMS_u4 = OpVariable %_ptr_UniformConstant_type_subpass_image_2 UniformConstant
+// CHECK: %SIMS_u4 = OpVariable %_ptr_UniformConstant_type_subpass_image_2 UniformConstant
 [[vk::input_attachment_index(10)]] SubpassInputMS<uint4>  SIMS_u4;
-// CHCK: %SIMS_f3 = OpVariable %_ptr_UniformConstant_type_subpass_image_3 UniformConstant
+// CHECK: %SIMS_f3 = OpVariable %_ptr_UniformConstant_type_subpass_image_3 UniformConstant
 [[vk::input_attachment_index(11)]] SubpassInputMS<float3> SIMS_f3;
-// CHCK: %SIMS_i2 = OpVariable %_ptr_UniformConstant_type_subpass_image_4 UniformConstant
+// CHECK: %SIMS_i2 = OpVariable %_ptr_UniformConstant_type_subpass_image_4 UniformConstant
 [[vk::input_attachment_index(12)]] SubpassInputMS<int2>   SIMS_i2;
-// CHCK: %SIMS_u1 = OpVariable %_ptr_UniformConstant_type_subpass_image_2 UniformConstant
+// CHECK: %SIMS_u1 = OpVariable %_ptr_UniformConstant_type_subpass_image_2 UniformConstant
 [[vk::input_attachment_index(13)]] SubpassInputMS<uint>   SIMS_u1;
 
+float4 ReadSourceFromTile(SubpassInput spi) {
+  return spi.SubpassLoad() ;
+}
+
 float4 main() : SV_Target {
 // CHECK:        [[img:%[0-9]+]] = OpLoad %type_subpass_image %SI_f4
 // CHECK-NEXT: [[texel:%[0-9]+]] = OpImageRead %v4float [[img]] [[v2i00]] None
@@ -60,6 +64,10 @@ float4 main() : SV_Target {
 // CHECK-NEXT:   [[val_1:%[0-9]+]] = OpCompositeExtract %float [[texel_2]] 0
 // CHECK-NEXT:                  OpStore %v3 [[val_1]]
     float  v3 = SI_f1.SubpassLoad();
+// CHECK:        [[val_2:%[0-9]+]] = OpFunctionCall %v4float %ReadSourceFromTile %param_var_spi
+// CHECK-NEXT:                    OpStore %v4 [[val_2]]
+    SubpassInput si = SI_f4;
+    float4 v4 = ReadSourceFromTile(si);
 
 // CHECK:        [[img_3:%[0-9]+]] = OpLoad %type_subpass_image_2 %SIMS_u4
 // CHECK-NEXT: [[texel_3:%[0-9]+]] = OpImageRead %v4uint [[img_3]] [[v2i00]] Sample %int_1
@@ -81,5 +89,5 @@ float4 main() : SV_Target {
 // CHECK-NEXT:                  OpStore %v13 [[val_4]]
     uint   v13 = SIMS_u1.SubpassLoad(4);
 
-    return v0.x + v1.y + v2.x + v3 + v10.x + v11.y + v12.x + v13;
+    return v0.x + v1.y + v2.x + v3 + v4.x + v10.x + v11.y + v12.x + v13;
 }

tools/clang/test/CodeGenSPIRV/vk.subpass-input.missing-attr.error.hlsl

@@ -1,15 +0,0 @@
-// RUN: not %dxc -T ps_6_0 -E main -fcgl  %s -spirv  2>&1 | FileCheck %s
-
-struct S {
-    float  a;
-    float2 b;
-    float  c;
-};
-
-SubpassInput SI0; // error
-
-void main() {
-
-}
-
-// CHECK:  :9:14: error: missing vk::input_attachment_index attribute