[llvm] [RemoveDIs] Fix spliceDebugInfo splice-to-end edge case (PR #105671)

[Orlando Cazalet-Hyams via llvm-commits]

https://github.com/OCHyams updated https://github.com/llvm/llvm-project/pull/105671

>From 282a7d19ac63274e062d7e30a5fd47160390c161 Mon Sep 17 00:00:00 2001
From: Orlando Cazalet-Hyams <orlando.hyams at sony.com>
Date: Thu, 22 Aug 2024 14:52:34 +0100
Subject: [PATCH 1/2] [RemoveDIs] Fix spliceDebugInfo splice-to-end edge case

Fix #105571 which demonstrates an end() iterator dereference when
performing a non-empty splice to end() from a region that ends at
Src::end().

Rather than calling Instruction::adoptDbgRecords from Dest, create a marker
(which takes an iterator) and absorbDebugValues onto that. The "absorb" variant
doesn't clean up the source marker, which in this case we know is a trailing
marker, so we have to do that manually.
---
 llvm/lib/IR/BasicBlock.cpp                  | 12 ++++-
 llvm/unittests/IR/BasicBlockDbgInfoTest.cpp | 54 +++++++++++++++++++++
 2 files changed, 64 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/IR/BasicBlock.cpp b/llvm/lib/IR/BasicBlock.cpp
index cf05b11c53963c..f2407bb3f37cd4 100644
--- a/llvm/lib/IR/BasicBlock.cpp
+++ b/llvm/lib/IR/BasicBlock.cpp
@@ -971,8 +971,16 @@ void BasicBlock::spliceDebugInfoImpl(BasicBlock::iterator Dest, BasicBlock *Src,
   if (ReadFromTail && Src->getMarker(Last)) {
     DbgMarker *FromLast = Src->getMarker(Last);
     if (LastIsEnd) {
-      Dest->adoptDbgRecords(Src, Last, true);
-      // adoptDbgRecords will release any trailers.
+      if (Dest == end()) {
+        // Abosrb the trailing markers from Src.
+        assert(FromLast == Src->getTrailingDbgRecords());
+        createMarker(Dest)->absorbDebugValues(*FromLast, true);
+        FromLast->eraseFromParent();
+        Src->deleteTrailingDbgRecords();
+      } else {
+        // adoptDbgRecords will release any trailers.
+        Dest->adoptDbgRecords(Src, Last, true);
+      }
       assert(!Src->getTrailingDbgRecords());
     } else {
       // FIXME: can we use adoptDbgRecords here to reduce allocations?
diff --git a/llvm/unittests/IR/BasicBlockDbgInfoTest.cpp b/llvm/unittests/IR/BasicBlockDbgInfoTest.cpp
index 91a0745a0cc76e..fc95f1838c3074 100644
--- a/llvm/unittests/IR/BasicBlockDbgInfoTest.cpp
+++ b/llvm/unittests/IR/BasicBlockDbgInfoTest.cpp
@@ -1525,4 +1525,58 @@ TEST(BasicBlockDbgInfoTest, DbgMoveToEnd) {
   EXPECT_FALSE(Ret->hasDbgRecords());
 }
 
+TEST(BasicBlockDbgInfoTest, DbgKnownSentinelCrash) {
+  return;
+  LLVMContext C;
+  std::unique_ptr<Module> M = parseIR(C, R"(
+    define i16 @foo(i16 %a) !dbg !6 {
+    entry:
+      %b = add i16 %a, 0
+        #dbg_value(i16 %b, !9, !DIExpression(), !11)
+      ret i16 0, !dbg !11
+    }
+
+    !llvm.dbg.cu = !{!0}
+    !llvm.module.flags = !{!5}
+
+    !0 = distinct !DICompileUnit(language: DW_LANG_C, file: !1, producer: "debugify", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+    !1 = !DIFile(filename: "t.ll", directory: "/")
+    !2 = !{}
+    !5 = !{i32 2, !"Debug Info Version", i32 3}
+    !6 = distinct !DISubprogram(name: "foo", linkageName: "foo", scope: null, file: !1, line: 1, type: !7, scopeLine: 1, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !8)
+    !7 = !DISubroutineType(types: !2)
+    !8 = !{!9}
+    !9 = !DILocalVariable(name: "1", scope: !6, file: !1, line: 1, type: !10)
+    !10 = !DIBasicType(name: "ty16", size: 16, encoding: DW_ATE_unsigned)
+    !11 = !DILocation(line: 1, column: 1, scope: !6)
+)");
+  ASSERT_TRUE(M);
+
+  Function *F = M->getFunction("foo");
+  BasicBlock &BB = F->getEntryBlock();
+  // Start with no trailing records.
+  ASSERT_FALSE(BB.getTrailingDbgRecords());
+
+  BasicBlock::iterator Ret = std::prev(BB.end());
+  BasicBlock::iterator B = std::prev(Ret);
+
+  // Delete terminator which has debug records: we now get trailing records.
+  Ret->eraseFromParent();
+  EXPECT_TRUE(BB.getTrailingDbgRecords());
+
+  BasicBlock *NewBB = BasicBlock::Create(C, "NewBB", F);
+  NewBB->splice(NewBB->end(), &BB, B, BB.end());
+
+  // The trailing records should've been absorbed into NewBB.
+  EXPECT_FALSE(BB.getTrailingDbgRecords());
+  EXPECT_TRUE(NewBB->getTrailingDbgRecords());
+  if (NewBB->getTrailingDbgRecords())
+    EXPECT_EQ(
+        llvm::range_size(NewBB->getTrailingDbgRecords()->getDbgRecordRange()),
+        1);
+
+  // Drop the trailing records now, to prevent a cleanup assertion.
+  NewBB->deleteTrailingDbgRecords();
+}
+
 } // End anonymous namespace.

>From e0f95a0aa1226e85b42a37b85b7a8d4e29bb156a Mon Sep 17 00:00:00 2001
From: Orlando Cazalet-Hyams <orlando.hyams at sony.com>
Date: Tue, 27 Aug 2024 13:26:24 +0100
Subject: [PATCH 2/2] remove early return, rename unittest & fix warnings

---
 llvm/unittests/IR/BasicBlockDbgInfoTest.cpp | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/llvm/unittests/IR/BasicBlockDbgInfoTest.cpp b/llvm/unittests/IR/BasicBlockDbgInfoTest.cpp
index fc95f1838c3074..e6f8df2762e81e 100644
--- a/llvm/unittests/IR/BasicBlockDbgInfoTest.cpp
+++ b/llvm/unittests/IR/BasicBlockDbgInfoTest.cpp
@@ -1525,8 +1525,7 @@ TEST(BasicBlockDbgInfoTest, DbgMoveToEnd) {
   EXPECT_FALSE(Ret->hasDbgRecords());
 }
 
-TEST(BasicBlockDbgInfoTest, DbgKnownSentinelCrash) {
-  return;
+TEST(BasicBlockDbgInfoTest, CloneTrailingRecordsToEmptyBlock) {
   LLVMContext C;
   std::unique_ptr<Module> M = parseIR(C, R"(
     define i16 @foo(i16 %a) !dbg !6 {
@@ -1570,10 +1569,11 @@ TEST(BasicBlockDbgInfoTest, DbgKnownSentinelCrash) {
   // The trailing records should've been absorbed into NewBB.
   EXPECT_FALSE(BB.getTrailingDbgRecords());
   EXPECT_TRUE(NewBB->getTrailingDbgRecords());
-  if (NewBB->getTrailingDbgRecords())
+  if (NewBB->getTrailingDbgRecords()) {
     EXPECT_EQ(
         llvm::range_size(NewBB->getTrailingDbgRecords()->getDbgRecordRange()),
-        1);
+        1u);
+  }
 
   // Drop the trailing records now, to prevent a cleanup assertion.
   NewBB->deleteTrailingDbgRecords();