[SPIRV] Add -fspv-flatten-resource-array-bindings-only

docs/ReleaseNotes.md

@@ -22,6 +22,12 @@ The included licenses apply to the following files:
 Place release notes for the upcoming release below this line and remove this
 line upon naming the release. Refer to previous for appropriate section names.
 
+#### SPIR-V
+
+- Added `-fspv-flatten-resource-array-bindings-only`, which reserves one
+  binding number per array element for arrays of resources without splitting
+  the array into separate SPIR-V variables/bindings.
+
 ### Upcoming Preview Release
 
 These changes apply to experimental preview shader models only and will not be

docs/SPIR-V.rst

@@ -4289,6 +4289,14 @@ codegen for Vulkan:
   SPIR-V backend. Also note that this requires the optimizer to be able to
   resolve all array accesses with constant indeces. Therefore, all loops using
   the resource arrays must be marked with ``[unroll]``.
+- ``-fspv-flatten-resource-array-bindings-only``: Reserves one binding number
+  per array element for arrays of resources, matching the binding numbers
+  that ``-fspv-flatten-resource-arrays`` would reserve, but keeps each array
+  as a single SPIR-V variable/binding (with ``descriptorCount`` equal to the
+  array size) instead of splitting it into one variable per element. Use this
+  when you want later-declared resources to avoid overlapping the numbers an
+  array would need under DX, without requiring the array itself to be
+  split up or unrolled.
 - ``-fspv-entrypoint-name=<name>``: Specify the SPIR-V entry point name. Defaults
   to the HLSL entry point name.
 - ``-fspv-use-legacy-buffer-matrix-order``: Assumes the legacy matrix order (row

include/dxc/Support/HLSLOptions.td

@@ -405,6 +405,8 @@ def fspv_target_env_EQ : Joined<["-"], "fspv-target-env=">, Group<spirv_Group>,
   HelpText<"Specify the target environment: vulkan1.0 (default), vulkan1.1, vulkan1.1spirv1.4, vulkan1.2, vulkan1.3, or universal1.5">;
 def fspv_flatten_resource_arrays: Flag<["-"], "fspv-flatten-resource-arrays">, Group<spirv_Group>, Flags<[CoreOption, DriverOption]>,
   HelpText<"Flatten arrays of resources so each array element takes one binding number">;
+def fspv_flatten_resource_array_bindings_only: Flag<["-"], "fspv-flatten-resource-array-bindings-only">, Group<spirv_Group>, Flags<[CoreOption, DriverOption]>,
+  HelpText<"Reserve one binding number per array element for arrays of resources, without splitting the array into separate variables">;
 def fspv_reduce_load_size: Flag<["-"], "fspv-reduce-load-size">, Group<spirv_Group>, Flags<[CoreOption, DriverOption]>,
   HelpText<"Replaces loads of composite objects to reduce memory pressure for the loads">;
 def fspv_fix_func_call_arguments: Flag<["-"], "fspv-fix-func-call-arguments">, Group<spirv_Group>, Flags<[CoreOption, DriverOption, HelpHidden]>,

include/dxc/Support/SPIRVOptions.h

@@ -64,6 +64,7 @@ struct SpirvCodeGenOptions {
   bool useLegacyBufferMatrixOrder = false;
   bool useScalarLayout = false;
   bool flattenResourceArrays = false;
+  bool flattenResourceArrayBindingsOnly = false;
   bool reduceLoadSize = false;
   bool autoShiftBindings = false;
   bool supportNonzeroBaseInstance = false;

lib/DxcSupport/HLSLOptions.cpp

@@ -1120,6 +1120,8 @@ int ReadDxcOpts(const OptTable *optionTable, unsigned flagsToInclude,
       Args.hasFlag(OPT_Wno_vk_emulated_features, OPT_INVALID, false);
   opts.SpirvOptions.flattenResourceArrays =
       Args.hasFlag(OPT_fspv_flatten_resource_arrays, OPT_INVALID, false);
+  opts.SpirvOptions.flattenResourceArrayBindingsOnly = Args.hasFlag(
+      OPT_fspv_flatten_resource_array_bindings_only, OPT_INVALID, false);
   opts.SpirvOptions.reduceLoadSize =
       Args.hasFlag(OPT_fspv_reduce_load_size, OPT_INVALID, false);
   opts.SpirvOptions.fixFuncCallArguments =
@@ -1294,6 +1296,8 @@ int ReadDxcOpts(const OptTable *optionTable, unsigned flagsToInclude,
       Args.hasFlag(OPT_fspv_use_legacy_buffer_matrix_order, OPT_INVALID,
                    false) ||
       Args.hasFlag(OPT_fspv_flatten_resource_arrays, OPT_INVALID, false) ||
+      Args.hasFlag(OPT_fspv_flatten_resource_array_bindings_only, OPT_INVALID,
+                   false) ||
       Args.hasFlag(OPT_fspv_reduce_load_size, OPT_INVALID, false) ||
       Args.hasFlag(OPT_fspv_reflect, OPT_INVALID, false) ||
       Args.hasFlag(OPT_fspv_fix_func_call_arguments, OPT_INVALID, false) ||

tools/clang/lib/SPIRV/DeclResultIdMapper.cpp

@@ -2646,7 +2646,9 @@ bool DeclResultIdMapper::decorateResourceBindings() {
     // resources (e.g. array of textures), DX uses one binding number per array
     // element. We can match this behavior via a command line option.
     uint32_t numBindingsToUse = 1;
-    if (spirvOptions.flattenResourceArrays || needsFlatteningCompositeResources)
+    if (spirvOptions.flattenResourceArrays ||
+        spirvOptions.flattenResourceArrayBindingsOnly ||
+        needsFlatteningCompositeResources)
       numBindingsToUse = getNumBindingsUsedByResourceType(
           var.getSpirvInstr()->getAstResultType());
 
@@ -2736,7 +2738,9 @@ bool DeclResultIdMapper::decorateResourceBindings() {
     // resources (e.g. array of textures), DX uses one binding number per array
     // element. We can match this behavior via a command line option.
     uint32_t numBindingsToUse = 1;
-    if (spirvOptions.flattenResourceArrays || needsFlatteningCompositeResources)
+    if (spirvOptions.flattenResourceArrays ||
+        spirvOptions.flattenResourceArrayBindingsOnly ||
+        needsFlatteningCompositeResources)
       numBindingsToUse = getNumBindingsUsedByResourceType(
           var.getSpirvInstr()->getAstResultType());
 

tools/clang/test/CodeGenSPIRV/vk.binding.cl.flatten-array-bindings-only.example1-optimized.hlsl

@@ -0,0 +1,27 @@
+// RUN: %dxc -T ps_6_0 -E main -fspv-flatten-resource-array-bindings-only -O3  %s -spirv | FileCheck %s
+
+// The array is NOT split into individual variables (unlike
+// -fspv-flatten-resource-arrays): MyTextures/MySamplers stay as single
+// array variables, each with a single Binding decoration, but the binding
+// numbers reserved for them still account for the full array size.
+// CHECK: OpDecorate %MyTextures Binding 0
+// CHECK: OpDecorate %AnotherTexture Binding 5
+// CHECK: OpDecorate %NextTexture Binding 6
+// CHECK: OpDecorate %MySamplers Binding 7
+// CHECK-NOT: MyTextures_0_
+// CHECK-NOT: MySamplers_0_
+Texture2D    MyTextures[5] : register(t0);
+Texture2D    NextTexture;  // This is suppose to be t6.
+Texture2D    AnotherTexture : register(t5);
+SamplerState MySamplers[2];
+
+[unroll]
+float4 main(float2 TexCoord : TexCoord) : SV_Target0
+{
+  float4 result = 0;
+  for (uint i = 0; i < 5; ++i)
+    result += MyTextures[i].Sample(MySamplers[i < 3 ? 0 : 1], TexCoord);
+  result += AnotherTexture.Sample(MySamplers[1], TexCoord);
+  result += NextTexture.Sample(MySamplers[1], TexCoord);
+  return result;
+}

tools/clang/test/CodeGenSPIRV/vk.binding.cl.flatten-array-bindings-only.example1.hlsl

@@ -0,0 +1,23 @@
+// RUN: %dxc -T ps_6_0 -E main -fspv-flatten-resource-array-bindings-only -fcgl  %s -spirv | FileCheck %s
+
+// CHECK: OpDecorate %MyTextures Binding 0
+// CHECK: OpDecorate %AnotherTexture Binding 5
+// CHECK: OpDecorate %NextTexture Binding 6
+// CHECK: OpDecorate %MySamplers Binding 7
+Texture2D    MyTextures[5] : register(t0);
+Texture2D    NextTexture;  // This is suppose to be t6.
+Texture2D    AnotherTexture : register(t5);
+SamplerState MySamplers[2];
+
+float4 main(float2 TexCoord : TexCoord) : SV_Target0
+{
+  float4 result =
+    MyTextures[0].Sample(MySamplers[0], TexCoord) +
+    MyTextures[1].Sample(MySamplers[0], TexCoord) +
+    MyTextures[2].Sample(MySamplers[0], TexCoord) +
+    MyTextures[3].Sample(MySamplers[1], TexCoord) +
+    MyTextures[4].Sample(MySamplers[1], TexCoord) +
+    AnotherTexture.Sample(MySamplers[1], TexCoord) +
+    NextTexture.Sample(MySamplers[1], TexCoord);
+  return result;
+}