[llvm] [llvm-c] Add missing nullptr check in LLVMGetFirstDbgRecord (PR #151101)

[Maxime Arthaud via llvm-commits]

https://github.com/arthaud updated https://github.com/llvm/llvm-project/pull/151101

>From e12de59a585c87b06a61bd29a4b430ea7d9e3592 Mon Sep 17 00:00:00 2001
From: Maxime Arthaud <maxime at arthaud.me>
Date: Tue, 29 Jul 2025 10:35:06 +0200
Subject: [PATCH] [llvm-c] Add missing nullptr check in LLVMGetFirstDbgRecord

Fix a crash when calling LLVMGetFirstDbgRecord or LLVMGetLastDbgRecord
on instructions without debug markers.
---
 llvm/lib/IR/Core.cpp               | 4 ++++
 llvm/tools/llvm-c-test/debuginfo.c | 7 +++++++
 2 files changed, 11 insertions(+)

diff --git a/llvm/lib/IR/Core.cpp b/llvm/lib/IR/Core.cpp
index f7ef4aa473ef5..56190545eb024 100644
--- a/llvm/lib/IR/Core.cpp
+++ b/llvm/lib/IR/Core.cpp
@@ -2984,6 +2984,8 @@ LLVMValueRef LLVMIsATerminatorInst(LLVMValueRef Inst) {
 
 LLVMDbgRecordRef LLVMGetFirstDbgRecord(LLVMValueRef Inst) {
   Instruction *Instr = unwrap<Instruction>(Inst);
+  if (!Instr->DebugMarker)
+    return nullptr;
   auto I = Instr->DebugMarker->StoredDbgRecords.begin();
   if (I == Instr->DebugMarker->StoredDbgRecords.end())
     return nullptr;
@@ -2992,6 +2994,8 @@ LLVMDbgRecordRef LLVMGetFirstDbgRecord(LLVMValueRef Inst) {
 
 LLVMDbgRecordRef LLVMGetLastDbgRecord(LLVMValueRef Inst) {
   Instruction *Instr = unwrap<Instruction>(Inst);
+  if (!Instr->DebugMarker)
+    return nullptr;
   auto I = Instr->DebugMarker->StoredDbgRecords.rbegin();
   if (I == Instr->DebugMarker->StoredDbgRecords.rend())
     return nullptr;
diff --git a/llvm/tools/llvm-c-test/debuginfo.c b/llvm/tools/llvm-c-test/debuginfo.c
index e73f69743805c..4d25673326fc1 100644
--- a/llvm/tools/llvm-c-test/debuginfo.c
+++ b/llvm/tools/llvm-c-test/debuginfo.c
@@ -325,6 +325,13 @@ int llvm_test_dibuilder(void) {
   LLVMValueRef Phi2 = LLVMBuildPhi(Builder, I64, "p2");
   LLVMAddIncoming(Phi2, &Zero, &FooEntryBlock, 1);
 
+  // Test that LLVMGetFirstDbgRecord and LLVMGetLastDbgRecord return NULL for
+  // instructions without debug info.
+  LLVMDbgRecordRef Phi1FirstDbgRecord = LLVMGetFirstDbgRecord(Phi1);
+  assert(Phi1FirstDbgRecord == NULL);
+  LLVMDbgRecordRef Phi1LastDbgRecord = LLVMGetLastDbgRecord(Phi1);
+  assert(Phi1LastDbgRecord == NULL);
+
   // Insert a non-phi before the `ret` but not before the debug records to
   // test that works as expected.
   LLVMPositionBuilder(Builder, FooVarBlock, Ret);