[spirv] Fix counter_binding precedence and test (#1363)

A missing `else` made it possible for a resource variable with a
corresponding counter variable that was defined with both
vk::binding and :register, each indicating a different descriptor
set to have the main variable assigned the set indicated by
vk::binding while the counter went to the set indicated by the register

Adds a new test for this and other such conditions.

tools/clang/lib/SPIRV/DeclResultIdMapper.cpp

@@ -1131,7 +1131,7 @@ bool DeclResultIdMapper::decorateResourceBindings() {
         uint32_t set = 0;
         if (const auto *vkBinding = var.getBinding())
           set = vkBinding->getSet();
-        if (const auto *reg = var.getRegister())
+        else if (const auto *reg = var.getRegister())
           set = reg->RegisterSpace;
 
         tryToDecorate(var.getSpirvId(), set, vkCBinding->getBinding());

tools/clang/test/CodeGenSPIRV/vk.binding.precedence.hlsl

@@ -0,0 +1,62 @@
+// Run: %dxc -T ps_6_0 -E main
+
+struct S {
+    float4 f;
+};
+
+// Verify that descriptor set-indicating override per: vk::binding > :register
+// using variations on these and vk::counter_binding
+
+// explicit set vk::binding > :register
+[[vk::binding(5, 4)]]
+RWBuffer<float4> exBindVsReg : register(u6, space7);
+// CHECK:      OpDecorate %exBindVsReg DescriptorSet 4
+// CHECK-NEXT: OpDecorate %exBindVsReg Binding 5
+
+// implicit set vk::binding > :register
+[[vk::binding(8)]]
+cbuffer impBindVsReg : register(b9, space1) {
+    float cbfield;
+};
+// CHECK:      OpDecorate %impBindVsReg DescriptorSet 0
+// CHECK-NEXT: OpDecorate %impBindVsReg Binding 8
+
+// explicit set vk::binding > :register explicit counter
+[[vk::binding(4,1), vk::counter_binding(5)]]
+RWStructuredBuffer<S> exBindVsRegExCt : register(u4, space9);
+// CHECK:      OpDecorate %exBindVsRegExCt DescriptorSet 1
+// CHECK-NEXT: OpDecorate %exBindVsRegExCt Binding 4
+// CHECK-NEXT: OpDecorate %counter_var_exBindVsRegExCt DescriptorSet 1
+// CHECK-NEXT: OpDecorate %counter_var_exBindVsRegExCt Binding 5
+
+// implicit set vk::binding > :register explicit counter
+[[vk::binding(2), vk::counter_binding(5)]]
+AppendStructuredBuffer<S> impBindVsRegExCt;
+// CHECK-NEXT: OpDecorate %impBindVsRegExCt DescriptorSet 0
+// CHECK-NEXT: OpDecorate %impBindVsRegExCt Binding 2
+// CHECK-NEXT: OpDecorate %counter_var_impBindVsRegExCt DescriptorSet 0
+// CHECK-NEXT: OpDecorate %counter_var_impBindVsRegExCt Binding 5
+
+// explicit set vk::binding > :register implicit counter (main part)
+[[vk::binding(4, 3)]]
+ConsumeStructuredBuffer<S> exBindVsRegImpCt : register(u3, space9);
+// CHECK:      OpDecorate %exBindVsRegImpCt DescriptorSet 3
+// CHECK-NEXT: OpDecorate %exBindVsRegImpCt Binding 4
+
+// implicit set vk::binding > :register implicit counter (main part)
+[[vk::binding(12)]]
+RWStructuredBuffer<S> impBindVsRegImpCt : register(u9, space4);
+// CHECK:      OpDecorate %impBindVsRegImpCt DescriptorSet 0
+// CHECK-NEXT: OpDecorate %impBindVsRegImpCt Binding 12
+
+// explicit set vk::binding > :register implicit counter (counter part)
+// CHECK:      OpDecorate %counter_var_exBindVsRegImpCt DescriptorSet 3
+// CHECK-NEXT: OpDecorate %counter_var_exBindVsRegImpCt Binding 0
+
+// implicit set vk::binding > :register implicit counter (counter part)
+// CHECK:      OpDecorate %counter_var_impBindVsRegImpCt DescriptorSet 0
+// CHECK-NEXT: OpDecorate %counter_var_impBindVsRegImpCt Binding 0
+
+float4 main() : SV_Target {
+    return 1.0;
+}

tools/clang/unittests/SPIRV/CodeGenSPIRVTest.cpp

@@ -1340,6 +1340,10 @@ TEST_F(FileTest, VulkanImplicitBinding) {
   // Resource binding from neither [[vk::binding()]] or :register()
   runFileTest("vk.binding.implicit.hlsl");
 }
+TEST_F(FileTest, VulkanPrecedenceBinding) {
+  // Bindings from vk::binding and :register competing for dominance
+  runFileTest("vk.binding.precedence.hlsl");
+}
 TEST_F(FileTest, VulkanRegisterBinding) {
   // Resource binding from :register()
   runFileTest("vk.binding.register.hlsl");