add DXIL & basic access tests

Author: Keenuts

clang/test/CodeGenHLSL/vk-features/vk.pushconstant.access.hlsl

@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 -triple spirv-pc-vulkan-compute -x hlsl -emit-llvm -finclude-default-header -disable-llvm-passes -o - %s | FileCheck %s
+
+struct S {
+  uint value;
+};
+// CHECK: %struct.S = type { i32 }
+
+[[vk::push_constant]] S buffer;
+// CHECK: @buffer = external hidden addrspace(13) externally_initialized global %struct.S, align 1
+
+[numthreads(1, 1, 1)]
+void main() {
+  uint32_t v = buffer.value;
+// CHECK:  %[[#REG:]] = load i32, ptr addrspace(13) @buffer, align 1
+// CHECK:             store i32 %[[#REG]], ptr %v, align 4
+}

clang/test/CodeGenHLSL/vk-features/vk.pushconstant.dxil.hlsl

@@ -0,0 +1,18 @@
+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.6-compute -x hlsl -emit-llvm -finclude-default-header -disable-llvm-passes -o - %s | FileCheck %s
+
+struct S {
+  uint value;
+};
+// CHECK: %struct.S = type { i32 }
+
+[[vk::push_constant]] S buffer;
+// When targeting DXIL, the attribute is ignored, meaning this variable
+// is part of the implicit cbuffer.
+// CHECK: @buffer = external hidden addrspace(2) global %struct.S, align 1
+
+[numthreads(1, 1, 1)]
+void main() {
+  uint32_t v = buffer.value;
+// CHECK:  %[[#REG:]] = load i32, ptr addrspace(2) @buffer, align 1
+// CHECK:             store i32 %[[#REG]], ptr %v, align 4
+}