[llvm] [DirectX] Strip `dx.rootsignatures` metadata during `dxil-prepare` (PR #145746)

[Finn Plummer via llvm-commits]

https://github.com/inbelic created https://github.com/llvm/llvm-project/pull/145746

The `dx.rootsignatures` metadata is not recognized in DXIL, so failure to remove this will cause validation errors.

This metadata is parsed (within `RootSignatureAnalysisWrapper`) into its binary format. As such, once it has been used to construct the binary form, it can be safely discarded without loss of information.

This pr ensures that the dxil prepare pass will depend and preserve on the root signature analysis so that it runs before the metadata is removed.

- Update `DXILPrepare.cpp` to preserve and depend on `RootSignatureAnalysisWrapper`
- Update test to demonstrate order is correct
- Provide test-case to demonstrate the metadata is removed

Resolves https://github.com/llvm/llvm-project/issues/145437.

>From b862eea070494099621d09f40a30cf61963e3546 Mon Sep 17 00:00:00 2001
From: Finn Plummer <canadienfinn at gmail.com>
Date: Wed, 25 Jun 2025 17:03:31 +0000
Subject: [PATCH 1/3] remove dx.rootsignatures metadata and ensure dependent
 pass runs before

Co-authored-by: Justin Bogner "mail at justinbogner.com"
---
 llvm/lib/Target/DirectX/DXILPrepare.cpp | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/llvm/lib/Target/DirectX/DXILPrepare.cpp b/llvm/lib/Target/DirectX/DXILPrepare.cpp
index cb58f4833631d..c8866bfefdfc5 100644
--- a/llvm/lib/Target/DirectX/DXILPrepare.cpp
+++ b/llvm/lib/Target/DirectX/DXILPrepare.cpp
@@ -11,6 +11,7 @@
 /// Language (DXIL).
 //===----------------------------------------------------------------------===//
 
+#include "DXILRootSignature.h"
 #include "DXILShaderFlags.h"
 #include "DirectX.h"
 #include "DirectXIRPasses/PointerTypeAnalysis.h"
@@ -286,12 +287,21 @@ class DXILPrepareModule : public ModulePass {
     }
     // Remove flags not for DXIL.
     cleanModuleFlags(M);
+
+    // dx.rootsignatures will have been parsed from its metadata form as its
+    // binary form as part of the RootSignatureAnalysisWrapper, so safely
+    // remove it as it is not recognized in DXIL
+    if (NamedMDNode *RootSignature = M.getNamedMetadata("dx.rootsignatures"))
+      RootSignature->eraseFromParent();
+
     return true;
   }
 
   DXILPrepareModule() : ModulePass(ID) {}
   void getAnalysisUsage(AnalysisUsage &AU) const override {
     AU.addRequired<DXILMetadataAnalysisWrapperPass>();
+    AU.addRequired<RootSignatureAnalysisWrapper>();
+    AU.addPreserved<RootSignatureAnalysisWrapper>();
     AU.addPreserved<ShaderFlagsAnalysisWrapper>();
     AU.addPreserved<DXILMetadataAnalysisWrapperPass>();
     AU.addPreserved<DXILResourceWrapperPass>();
@@ -305,6 +315,7 @@ char DXILPrepareModule::ID = 0;
 INITIALIZE_PASS_BEGIN(DXILPrepareModule, DEBUG_TYPE, "DXIL Prepare Module",
                       false, false)
 INITIALIZE_PASS_DEPENDENCY(DXILMetadataAnalysisWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(RootSignatureAnalysisWrapper)
 INITIALIZE_PASS_END(DXILPrepareModule, DEBUG_TYPE, "DXIL Prepare Module", false,
                     false)
 

>From 1fb6ff8f38767bb07c5b849ba6b7f6b2a8591bbf Mon Sep 17 00:00:00 2001
From: Finn Plummer <canadienfinn at gmail.com>
Date: Wed, 25 Jun 2025 17:04:13 +0000
Subject: [PATCH 2/3] add test to ensure pass order is corrected

---
 llvm/test/CodeGen/DirectX/llc-pipeline.ll | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/llvm/test/CodeGen/DirectX/llc-pipeline.ll b/llvm/test/CodeGen/DirectX/llc-pipeline.ll
index 2b29fd30a7a56..5934de2c9758a 100644
--- a/llvm/test/CodeGen/DirectX/llc-pipeline.ll
+++ b/llvm/test/CodeGen/DirectX/llc-pipeline.ll
@@ -33,13 +33,13 @@
 ; CHECK-NEXT:   DXIL Translate Metadata
 ; CHECK-NEXT:   DXIL Post Optimization Validation
 ; CHECK-NEXT:   DXIL Op Lowering
+; CHECK-NEXT: DXIL Root Signature Analysis
 ; CHECK-NEXT:   DXIL Prepare Module
 
 ; CHECK-ASM-NEXT: DXIL Metadata Pretty Printer
 ; CHECK-ASM-NEXT: Print Module IR
 
 ; CHECK-OBJ-NEXT: DXIL Embedder
-; CHECK-OBJ-NEXT: DXIL Root Signature Analysis
 ; CHECK-OBJ-NEXT: DXContainer Global Emitter
 ; CHECK-OBJ-NEXT: FunctionPass Manager
 ; CHECK-OBJ-NEXT:   Lazy Machine Block Frequency Analysis

>From 4cce9453be5238c40b0300595d05b63683a69147 Mon Sep 17 00:00:00 2001
From: Finn Plummer <canadienfinn at gmail.com>
Date: Wed, 25 Jun 2025 17:32:12 +0000
Subject: [PATCH 3/3] add test to ensure the metadata is removed during
 dxil-prepare

---
 .../CodeGen/DirectX/strip-rootsignatures.ll     | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)
 create mode 100644 llvm/test/CodeGen/DirectX/strip-rootsignatures.ll

diff --git a/llvm/test/CodeGen/DirectX/strip-rootsignatures.ll b/llvm/test/CodeGen/DirectX/strip-rootsignatures.ll
new file mode 100644
index 0000000000000..3b3ddf4886511
--- /dev/null
+++ b/llvm/test/CodeGen/DirectX/strip-rootsignatures.ll
@@ -0,0 +1,17 @@
+; RUN: opt -S -dxil-prepare < %s | FileCheck %s
+
+; Ensures that dxil-prepare will remove the dx.rootsignatures metadata
+
+target triple = "dxil-unknown-shadermodel6.0-compute"
+
+define void @main() {
+entry:
+  ret void
+}
+
+; CHECK-NOT: !dx.rootsignature
+
+!dx.rootsignatures = !{!2} ; list of function/root signature pairs
+!2 = !{ ptr @main, !3, i32 2 } ; function, root signature
+!3 = !{ !4 } ; list of root signature elements
+!4 = !{ !"RootFlags", i32 1 } ; 1 = allow_input_assembler_input_layout