[PATCH v2 18/50] helper-to-tcg: PrepareForOptPass, collect debuginfo

Debug information is collected before any non-preserving optimization
pass is ran.  Currently, only variable definitions are parsed, mapping a
Value * to a name and typename.

Signed-off-by: Anton Johansson <[email protected]>
---
 .../helper-to-tcg/include/DebugInfo.hpp       | 46 ++++++++++++++++
 .../include/PrepareForOptPass.hpp             | 10 ++--
 subprojects/helper-to-tcg/src/Pipeline.cpp    |  3 +-
 .../PrepareForOptPass/PrepareForOptPass.cpp   | 52 +++++++++++++++++++
 4 files changed, 107 insertions(+), 4 deletions(-)
 create mode 100644 subprojects/helper-to-tcg/include/DebugInfo.hpp

diff --git a/subprojects/helper-to-tcg/include/DebugInfo.hpp b/subprojects/helper-to-tcg/include/DebugInfo.hpp
new file mode 100644
index 0000000000..27e545c6b7
--- /dev/null
+++ b/subprojects/helper-to-tcg/include/DebugInfo.hpp
@@ -0,0 +1,46 @@
+//
+//  Copyright(c) 2026 rev.ng Labs Srl. All Rights Reserved.
+//
+//  This program is free software; you can redistribute it and/or modify
+//  it under the terms of the GNU General Public License as published by
+//  the Free Software Foundation; either version 2 of the License, or
+//  (at your option) any later version.
+//
+//  This program is distributed in the hope that it will be useful,
+//  but WITHOUT ANY WARRANTY; without even the implied warranty of
+//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//  GNU General Public License for more details.
+//
+//  You should have received a copy of the GNU General Public License
+//  along with this program; if not, see <http://www.gnu.org/licenses/>.
+//
+
+#pragma once
+
+#include <llvm/ADT/StringRef.h>
+#include <llvm/IR/ValueMap.h>
+
+namespace llvm {
+class Value;
+}
+
+// StringRefs will refer do debug metadata fields which have the same
+// lifetime as the LLVMContext and survive accross optimizations and
+// possible deletions of functions/variables.
+struct DebugInfo {
+    llvm::StringRef VarName;
+    llvm::StringRef BaseTypeName;
+};
+
+using DebugInfoMapTy = llvm::ValueMap<const llvm::Value *, DebugInfo>;
+
+// Helper to get the variable name from debug info associated with a particular
+// value, or default construct an empty name.
+inline llvm::StringRef getDebugVarName(const DebugInfoMapTy &DM,
+                                       const llvm::Value *V) {
+    auto It = DM.find(V);
+    if (It != DM.end()) {
+        return It->second.VarName;
+    }
+    return {};
+}
diff --git a/subprojects/helper-to-tcg/include/PrepareForOptPass.hpp b/subprojects/helper-to-tcg/include/PrepareForOptPass.hpp
index 08ca9a43bb..43cf77190a 100644
--- a/subprojects/helper-to-tcg/include/PrepareForOptPass.hpp
+++ b/subprojects/helper-to-tcg/include/PrepareForOptPass.hpp
@@ -17,6 +17,7 @@
 
 #pragma once
 
+#include "DebugInfo.hpp"
 #include "FunctionAnnotation.hpp"
 #include <llvm/IR/PassManager.h>
 
@@ -29,10 +30,13 @@
 
 class PrepareForOptPass : public llvm::PassInfoMixin<PrepareForOptPass> {
     AnnotationMapTy &ResultAnnotations;
+    DebugInfoMapTy &ResultDebugInfo;
 
-  public:
-    PrepareForOptPass(AnnotationMapTy &ResultAnnotations)
-        : ResultAnnotations(ResultAnnotations) {}
+public:
+    PrepareForOptPass(AnnotationMapTy &ResultAnnotations,
+                      DebugInfoMapTy &ResultDebugInfo)
+        : ResultAnnotations(ResultAnnotations),
+          ResultDebugInfo(ResultDebugInfo) {}
     llvm::PreservedAnalyses run(llvm::Module &M,
                                 llvm::ModuleAnalysisManager &MAM);
 };
diff --git a/subprojects/helper-to-tcg/src/Pipeline.cpp b/subprojects/helper-to-tcg/src/Pipeline.cpp
index 89637eaec6..a11c5fd353 100644
--- a/subprojects/helper-to-tcg/src/Pipeline.cpp
+++ b/subprojects/helper-to-tcg/src/Pipeline.cpp
@@ -193,7 +193,8 @@ int main(int argc, char **argv) {
     // but is correlct in LLVM-terms.
 
     AnnotationMapTy Annotations;
-    MPM.addPass(PrepareForOptPass(Annotations));
+    DebugInfoMapTy DebugInfo;
+    MPM.addPass(PrepareForOptPass(Annotations, DebugInfo));
 
     {
         FunctionPassManager FPM;
diff --git a/subprojects/helper-to-tcg/src/PrepareForOptPass/PrepareForOptPass.cpp b/subprojects/helper-to-tcg/src/PrepareForOptPass/PrepareForOptPass.cpp
index a7bee53582..7a9b954d7c 100644
--- a/subprojects/helper-to-tcg/src/PrepareForOptPass/PrepareForOptPass.cpp
+++ b/subprojects/helper-to-tcg/src/PrepareForOptPass/PrepareForOptPass.cpp
@@ -26,6 +26,9 @@
 #include <llvm/ADT/StringSet.h>
 #include <llvm/Demangle/Demangle.h>
 #include <llvm/IR/Constants.h>
+#if LLVM_VERSION_MAJOR >= 19
+#include <llvm/IR/DebugProgramInstruction.h>
+#endif
 #include <llvm/IR/Function.h>
 #include <llvm/IR/Instruction.h>
 #include <llvm/IR/Instructions.h>
@@ -288,6 +291,53 @@ static void replaceRetaddrWithUndef(Module &M) {
     }
 }
 
+static void collectDebugInfo(Function &F, DebugInfoMapTy &ResultDebugInfo) {
+    StringSet EncounteredNames;
+    for (auto &BB : F) {
+        for (Instruction &I : BB) {
+#if LLVM_VERSION_MAJOR >= 19
+            for (DbgVariableRecord &DVR :
+                 filterDbgVars(I.getDbgRecordRange())) {
+                if (!DVR.isDbgValue()) {
+                    continue;
+                }
+                StringRef BaseType{};
+                StringRef VarName{};
+                if (auto *Derived =
+                        dyn_cast<DIDerivedType>(DVR.getVariable()->getType())) {
+                    BaseType = Derived->getBaseType()->getName();
+                }
+                VarName = DVR.getVariable()->getName();
+                if (ResultDebugInfo.find(DVR.getValue(0)) ==
+                        ResultDebugInfo.end() and
+                    !EncounteredNames.contains(VarName.data())) {
+                    ResultDebugInfo[DVR.getValue(0)] = {VarName, BaseType};
+                    EncounteredNames.insert(VarName.data());
+                }
+            }
+#else
+            if (I.isDebugOrPseudoInst()) {
+                if (const auto *Dbg = dyn_cast<DbgValueInst>(&I)) {
+                    StringRef BaseType{};
+                    StringRef VarName{};
+                    if (auto *Derived = dyn_cast<DIDerivedType>(
+                            Dbg->getVariable()->getType())) {
+                        BaseType = Derived->getBaseType()->getName();
+                    }
+                    VarName = Dbg->getVariable()->getName();
+                    if (ResultDebugInfo.find(Dbg->getValue(0)) ==
+                            ResultDebugInfo.end() and
+                        !EncounteredNames.contains(VarName.data())) {
+                        ResultDebugInfo[Dbg->getValue(0)] = {VarName, BaseType};
+                        EncounteredNames.insert(VarName.data());
+                    }
+                }
+            }
+#endif
+        }
+    }
+}
+
 PreservedAnalyses PrepareForOptPass::run(Module &M,
                                          ModuleAnalysisManager &MAM) {
     demangleFunctionNames(M);
@@ -305,6 +355,8 @@ PreservedAnalyses PrepareForOptPass::run(Module &M,
         if (F.getReturnType()->isStructTy()) {
             F.addFnAttr(Attribute::AttrKind::AlwaysInline);
         }
+        // Populate variable and type names for `Value`s from debug info.
+        collectDebugInfo(F, ResultDebugInfo);
     }
 
     return PreservedAnalyses::none();
-- 
2.52.0