Omit .debug_aranges if it is empty

[playstation-edd]

SIE tracker: https://jira.sie.sony.com/browse/TOOLCHAIN-16575

[llvmbot]

@llvm/pr-subscribers-debuginfo

Author: Edd Dawson (playstation-edd)

Changes

SIE tracker: https://jira.sie.sony.com/browse/TOOLCHAIN-16575

---

Full diff: https://github.com/llvm/llvm-project/pull/99897.diff

2 Files Affected:

• (modified) llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp (+4-2)
• (modified) llvm/test/DebugInfo/omit-empty.ll (+1-1)

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 80cd5ec501f25..f88653146cc6f 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -2990,6 +2990,9 @@ struct ArangeSpan {
 // Emit a debug aranges section, containing a CU lookup for any
 // address we can tie back to a CU.
 void DwarfDebug::emitDebugARanges() {
+  if (ArangeLabels.empty())
+    return;
+
   // Provides a unique id per text section.
   MapVector<MCSection *, SmallVector<SymbolCU, 8>> SectionMap;
 
@@ -3012,8 +3015,7 @@ void DwarfDebug::emitDebugARanges() {
   for (auto &I : SectionMap) {
     MCSection *Section = I.first;
     SmallVector<SymbolCU, 8> &List = I.second;
-    if (List.size() < 1)
-      continue;
+    assert(!List.empty());
 
     // If we have no section (e.g. common), just write out
     // individual spans for each symbol.
diff --git a/llvm/test/DebugInfo/omit-empty.ll b/llvm/test/DebugInfo/omit-empty.ll
index 0267ec5556f11..351d3055e039b 100644
--- a/llvm/test/DebugInfo/omit-empty.ll
+++ b/llvm/test/DebugInfo/omit-empty.ll
@@ -1,4 +1,4 @@
-; RUN: %llc_dwarf %s -filetype=obj -o - | llvm-objdump -h - | FileCheck %s
+; RUN: %llc_dwarf %s -filetype=obj -generate-arange-section -o - | llvm-objdump -h - | FileCheck %s
 ; REQUIRES: object-emission
 
 ; CHECK-NOT: .debug_

[pogo59]

Seems quite reasonable. LGTM.

[playstation-edd]

After convincing myself that any List must be non-empty, I was confident that the early return could be placed above this loop. I replaced the dead check with an assert to avoid similar head scratching in future.

[pogo59]

I believe the assert is appropriate even without the early return. If ArangeLabels is empty, SectionMap will also be empty, and the loop body will not execute.

[playstation-edd]

Yep, agreed. Just wanted to explain why I touched this seemingly unrelated part, for posterity.