[SPIR-V] Don't flatten arrays during legalization (microsoft#6767)

When struct contains opaque resources, we must legalize the SPIR-V to
move those resources out of the struct (Vulkan doesn't allow composite
to store opaque resources).
Before this change, any resource array would also be flattened due to
the pass flattening everything by default.

Patched SPIRV-Tools to allow some level of selection in what we flatten.
Not perfect, as we would flatten all arrays or all composites and cannot
pick only one variable to flatten, but for now this should be enough.

Fixes microsoft#6745
Signed-off-by: Nathan Gauër <brioche@google.com>

---------

Signed-off-by: Nathan Gauër <brioche@google.com>

Author: Keenuts

external/SPIRV-Headers

@@ -14805,13 +14805,19 @@ bool SpirvEmitter::spirvToolsLegalize(std::vector<uint32_t> *mod,
   }
   optimizer.RegisterLegalizationPasses(spirvOptions.preserveInterface);
   // Add flattening of resources if needed.
-  if (spirvOptions.flattenResourceArrays ||
-      declIdMapper.requiresFlatteningCompositeResources()) {
+  if (spirvOptions.flattenResourceArrays) {
     optimizer.RegisterPass(
         spvtools::CreateReplaceDescArrayAccessUsingVarIndexPass());
     optimizer.RegisterPass(
         spvtools::CreateAggressiveDCEPass(spirvOptions.preserveInterface));
-    optimizer.RegisterPass(spvtools::CreateDescriptorScalarReplacementPass());
+    optimizer.RegisterPass(
+        spvtools::CreateDescriptorArrayScalarReplacementPass());
+    optimizer.RegisterPass(
+        spvtools::CreateAggressiveDCEPass(spirvOptions.preserveInterface));
+  }
+  if (declIdMapper.requiresFlatteningCompositeResources()) {
+    optimizer.RegisterPass(
+        spvtools::CreateDescriptorCompositeScalarReplacementPass());
     // ADCE should be run after desc_sroa in order to remove potentially
     // illegal types such as structures containing opaque types.
     optimizer.RegisterPass(

external/SPIRV-Tools

@@ -0,0 +1,32 @@
+// RUN: %dxc -T ps_6_6 -E main -spirv %s | FileCheck %s
+
+// CHECK-DAG: OpName %Textures "Textures"
+// CHECK-DAG: OpDecorate %Textures DescriptorSet 0
+// CHECK-DAG: OpDecorate %Textures Binding 0
+Texture2D<float4> Textures[10];
+
+struct StructOfResources {
+    Texture2D Texture;
+    SamplerState Sampler;
+};
+
+// CHECK-DAG: OpName %TheStruct_Texture "TheStruct.Texture"
+// CHECK-DAG: OpDecorate %TheStruct_Texture DescriptorSet 0
+// CHECK-DAG: OpDecorate %TheStruct_Texture Binding 10
+
+// CHECK-DAG: OpName %TheStruct_Sampler "TheStruct.Sampler"
+// CHECK-DAG: OpDecorate %TheStruct_Sampler DescriptorSet 0
+// CHECK-DAG: OpDecorate %TheStruct_Sampler Binding 11
+StructOfResources TheStruct;
+
+float4 main() : SV_Target
+{
+// CHECK: [[ptr:%[0-9]+]] = OpAccessChain %_ptr_UniformConstant_type_2d_image %Textures %int_0
+// CHECK: [[tex:%[0-9]+]] = OpLoad %type_2d_image [[ptr]]
+// CHECK: [[smp:%[0-9]+]] = OpLoad %type_sampler %TheStruct_Sampler
+// CHECK:   [[x:%[0-9]+]] = OpSampledImage %type_sampled_image [[tex]] [[smp]]
+  return Textures[0].Sample(TheStruct.Sampler, float2(0, 0))
+// CHECK: [[tex:%[0-9]+]] = OpLoad %type_2d_image %TheStruct_Texture
+// CHECK:   [[x:%[0-9]+]] = OpSampledImage %type_sampled_image [[tex]] [[smp]]
+       + TheStruct.Texture.Sample(TheStruct.Sampler, float2(0, 0));
+}