[HLSL][RootSignature] Add metadata generation for descriptor tables (#139633)

- prereq: Modify `RootSignatureAttr` to hold a reference to the owned
declaration
- Define and implement `MetadataBuilder` in `HLSLRootSignature`
- Integrate and invoke the builder in `CGHLSLRuntime.cpp` to generate
the Root Signature for any associated entry functions
- Add tests to demonstrate functionality in `RootSignature.hlsl`

Resolves https://github.com/llvm/llvm-project/issues/126584

Note: this is essentially just
https://github.com/llvm/llvm-project/pull/125131 rebased onto the new
approach of constructing a root signature decl, instead of holding the
elements in `AdditionalMembers`.

1 files changed, 31 insertions, 0 deletions

diff --git a/clang/test/CodeGenHLSL/RootSignature.hlsl b/clang/test/CodeGenHLSL/RootSignature.hlsl
new file mode 100644
index 000000000000..60e0dec175b8
--- /dev/null
+++ b/clang/test/CodeGenHLSL/RootSignature.hlsl
@@ -0,0 +1,31 @@
+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.3-library -emit-llvm -o - %s | FileCheck %s
+
+// CHECK: !dx.rootsignatures = !{![[#FIRST_ENTRY:]], ![[#SECOND_ENTRY:]]}
+
+// CHECK: ![[#FIRST_ENTRY]] = !{ptr @FirstEntry, ![[#EMPTY:]]}
+// CHECK: ![[#EMPTY]] = !{}
+
+[shader("compute"), RootSignature("")]
+[numthreads(1,1,1)]
+void FirstEntry() {}
+
+// CHECK: ![[#SECOND_ENTRY]] = !{ptr @SecondEntry, ![[#SECOND_RS:]]}
+// CHECK: ![[#SECOND_RS]] = !{![[#TABLE:]]}
+// CHECK: ![[#TABLE]] = !{!"DescriptorTable", i32 0, ![[#CBV:]], ![[#SRV:]]}
+// CHECK: ![[#CBV]] = !{!"CBV", i32 1, i32 0, i32 0, i32 -1, i32 4}
+// CHECK: ![[#SRV]] = !{!"SRV", i32 4, i32 42, i32 3, i32 32, i32 0}
+
+#define SampleDescriptorTable \
+  "DescriptorTable( " \
+  "  CBV(b0), " \
+  "  SRV(t42, space = 3, offset = 32, numDescriptors = 4, flags = 0) " \
+  ")"
+[shader("compute"), RootSignature(SampleDescriptorTable)]
+[numthreads(1,1,1)]
+void SecondEntry() {}
+
+// Sanity test to ensure no root is added for this function as there is only
+// two entries in !dx.roosignatures
+[shader("compute")]
+[numthreads(1,1,1)]
+void ThirdEntry() {}