[llvm] Add CodeView S_LABEL32 symbols for jump table targets (for Windows debugging) (PR #146121)

[via llvm-commits]

https://github.com/sivadeilra updated https://github.com/llvm/llvm-project/pull/146121

>From aed08033f79a49983c7a73ff2238de4de7afc134 Mon Sep 17 00:00:00 2001
From: Arlie Davis <ardavis at microsoft.com>
Date: Thu, 26 Jun 2025 17:09:51 -0700
Subject: [PATCH 1/2] working on jump table labels

---
 llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp | 33 ++++++++++++++++---
 llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h   |  1 +
 llvm/test/DebugInfo/COFF/jump-table.ll        |  9 +++++
 3 files changed, 38 insertions(+), 5 deletions(-)

diff --git a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
index 5e1b313b4d2fa..91cf7c17f7cb0 100644
--- a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
@@ -3566,15 +3566,38 @@ void CodeViewDebug::collectDebugInfoForJumpTables(const MachineFunction *MF,
           break;
         }
 
-        CurFn->JumpTables.push_back(
-            {EntrySize, Base, BaseOffset, Branch,
-             MF->getJTISymbol(JumpTableIndex, MMI->getContext()),
-             JTI.getJumpTables()[JumpTableIndex].MBBs.size()});
+        const MachineJumpTableEntry &JTE = JTI.getJumpTables()[JumpTableIndex];
+
+        JumpTableInfo CVJTI{EntrySize,
+                            Base,
+                            BaseOffset,
+                            Branch,
+                            MF->getJTISymbol(JumpTableIndex, MMI->getContext()),
+                            JTE.MBBs.size()};
+
+        for (const auto &MBB : JTE.MBBs) {
+          CVJTI.Cases.push_back(MBB->getSymbol());
+        }
+
+        CurFn->JumpTables.push_back(std::move(CVJTI));
       });
 }
 
 void CodeViewDebug::emitDebugInfoForJumpTables(const FunctionInfo &FI) {
-  for (auto JumpTable : FI.JumpTables) {
+  // Emit S_LABEL32 records for each jump target
+  for (const auto &JumpTable : FI.JumpTables) {
+    for (const auto &CaseSym : JumpTable.Cases) {
+      MCSymbol *LabelEnd = beginSymbolRecord(SymbolKind::S_LABEL32);
+      OS.AddComment("Offset and segment");
+      OS.emitCOFFSecRel32(CaseSym, 0);
+      OS.AddComment("Flags");
+      OS.emitInt8(0);
+      emitNullTerminatedSymbolName(OS, CaseSym->getName());
+      endSymbolRecord(LabelEnd);
+    }
+  }
+
+  for (const auto &JumpTable : FI.JumpTables) {
     MCSymbol *JumpTableEnd = beginSymbolRecord(SymbolKind::S_ARMSWITCHTABLE);
     if (JumpTable.Base) {
       OS.AddComment("Base offset");
diff --git a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h
index c862802d835d7..c2b878e52e1c3 100644
--- a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h
+++ b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h
@@ -146,6 +146,7 @@ class LLVM_LIBRARY_VISIBILITY CodeViewDebug : public DebugHandlerBase {
     const MCSymbol *Branch;
     const MCSymbol *Table;
     size_t TableSize;
+    std::vector<const MCSymbol *> Cases;
   };
 
   // For each function, store a vector of labels to its instructions, as well as
diff --git a/llvm/test/DebugInfo/COFF/jump-table.ll b/llvm/test/DebugInfo/COFF/jump-table.ll
index 3eda2438ea88a..be1de2be55788 100644
--- a/llvm/test/DebugInfo/COFF/jump-table.ll
+++ b/llvm/test/DebugInfo/COFF/jump-table.ll
@@ -118,6 +118,15 @@
 ; CV:         GlobalProcIdSym {
 ; CV:           DisplayName: func
 ; CV-NOT:     GlobalProcIdSym
+; CV:           LabelSym {
+; CV-NEXT:        Kind: S_LABEL32 (0x1105)
+; CV-NEXT:        CodeOffset: 0xC0
+; CV-NEXT:        Segment: 0x0
+; CV-NEXT:        Flags: 0x0
+; CV-NEXT:        Flags [ (0x0)
+; CV-NEXT:        ]
+; CV-NEXT:        DisplayName:
+; CV-NEXT:      }
 ; CV:           JumpTableSym {
 ; CV-NEXT:        Kind: S_ARMSWITCHTABLE (0x1159)
 ; CV-NEXT:        BaseOffset: 0x0

>From f3881a56ebb7ae1dae71f5fc83015c1093c3b951 Mon Sep 17 00:00:00 2001
From: Arlie Davis <arlie.davis at microsoft.com>
Date: Mon, 30 Jun 2025 22:29:04 -0700
Subject: [PATCH 2/2] PR feedback, style

---
 llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
index 91cf7c17f7cb0..87bc9a8035f50 100644
--- a/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp
@@ -3567,18 +3567,14 @@ void CodeViewDebug::collectDebugInfoForJumpTables(const MachineFunction *MF,
         }
 
         const MachineJumpTableEntry &JTE = JTI.getJumpTables()[JumpTableIndex];
-
         JumpTableInfo CVJTI{EntrySize,
                             Base,
                             BaseOffset,
                             Branch,
                             MF->getJTISymbol(JumpTableIndex, MMI->getContext()),
                             JTE.MBBs.size()};
-
-        for (const auto &MBB : JTE.MBBs) {
+        for (const auto &MBB : JTE.MBBs)
           CVJTI.Cases.push_back(MBB->getSymbol());
-        }
-
         CurFn->JumpTables.push_back(std::move(CVJTI));
       });
 }