[llvm] [llvm][ELF] Separate out .dwo bytes written in stats (PR #126165)

[Arthur Eubanks via llvm-commits]

https://github.com/aeubanks created https://github.com/llvm/llvm-project/pull/126165

So we can distinguish between debug info sections written to .dwo files and those written to the object file.

>From 981de24500b8fe2b1a85c3ef9df1a2f22b7895d8 Mon Sep 17 00:00:00 2001
From: Arthur Eubanks <aeubanks at google.com>
Date: Fri, 7 Feb 2025 01:15:23 +0000
Subject: [PATCH] [llvm][ELF] Separate out .dwo bytes written in stats

So we can distinguish between debug info sections written to .dwo files and those written to the object file.
---
 llvm/lib/MC/ELFObjectWriter.cpp    |  7 +++++--
 llvm/test/CodeGen/X86/dwo-stats.ll | 30 ++++++++++++++++++++++++++++++
 2 files changed, 35 insertions(+), 2 deletions(-)
 create mode 100644 llvm/test/CodeGen/X86/dwo-stats.ll

diff --git a/llvm/lib/MC/ELFObjectWriter.cpp b/llvm/lib/MC/ELFObjectWriter.cpp
index 5f586fe19a5bb4a..df3cd54daa3b7fc 100644
--- a/llvm/lib/MC/ELFObjectWriter.cpp
+++ b/llvm/lib/MC/ELFObjectWriter.cpp
@@ -71,9 +71,10 @@ STATISTIC(StrtabBytes, "Total size of SHT_STRTAB sections");
 STATISTIC(SymtabBytes, "Total size of SHT_SYMTAB sections");
 STATISTIC(RelocationBytes, "Total size of relocation sections");
 STATISTIC(DynsymBytes, "Total size of SHT_DYNSYM sections");
-STATISTIC(DebugBytes, "Total size of debug info sections");
+STATISTIC(DebugBytes, "Total size of debug info sections (not including those written to .dwo)");
 STATISTIC(UnwindBytes, "Total size of unwind sections");
 STATISTIC(OtherBytes, "Total size of uncategorized sections");
+STATISTIC(DwoBytes, "Total size of sections written to .dwo file");
 
 } // namespace stats
 
@@ -969,7 +970,9 @@ void ELFWriter::writeSectionHeaders(const MCAssembler &Asm) {
       return Section->getFlags() & Flag;
     };
 
-    if (Section->getName().starts_with(".debug")) {
+    if (Mode == DwoOnly) {
+      stats::DwoBytes += Size;
+    } else if (Section->getName().starts_with(".debug")) {
       stats::DebugBytes += Size;
     } else if (Section->getName().starts_with(".eh_frame")) {
       stats::UnwindBytes += Size;
diff --git a/llvm/test/CodeGen/X86/dwo-stats.ll b/llvm/test/CodeGen/X86/dwo-stats.ll
new file mode 100644
index 000000000000000..fccfd55029c8bc1
--- /dev/null
+++ b/llvm/test/CodeGen/X86/dwo-stats.ll
@@ -0,0 +1,30 @@
+; REQUIRES: asserts
+; RUN: llc %s -mtriple=x86_64-linux --split-dwarf-file=%t.dwo --split-dwarf-output=%t.dwo --filetype=obj -o /dev/null -stats 2>&1 | FileCheck %s --check-prefixes=SPLIT,CHECK
+; RUN: llc %s -mtriple=x86_64-linux --filetype=obj -o /dev/null -stats 2>&1 | FileCheck %s --check-prefixes=NOTSPLIT,CHECK
+
+; NOTSPLIT-NOT: {{[0-9]+}} elf-object-writer - Total size of sections written to .dwo file
+; CHECK-DAG: {{[0-9]+}} elf-object-writer - Total size of debug info sections
+; SPLIT-DAG: {{[0-9]+}} elf-object-writer - Total size of sections written to .dwo file
+; NOTSPLIT-NOT: {{[0-9]+}} elf-object-writer - Total size of sections written to .dwo file
+
+define void @banana() !dbg !8 {
+  ret void, !dbg !12
+}
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5, !6}
+!llvm.ident = !{!7}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 11.0.1", isOptimized: true, runtimeVersion: 0, splitDebugFilename: "test.dwo", emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: GNU)
+!1 = !DIFile(filename: "/tmp/test.c", directory: "/tmp")
+!2 = !{}
+!3 = !{i32 7, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{i32 7, !"PIC Level", i32 2}
+!7 = !{!"clang version 11.0.1"}
+!8 = distinct !DISubprogram(name: "banana", scope: !9, file: !9, line: 1, type: !10, scopeLine: 1, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2)
+!9 = !DIFile(filename: "test.c", directory: "/tmp")
+!10 = !DISubroutineType(types: !11)
+!11 = !{null}
+!12 = !DILocation(line: 1, column: 20, scope: !8)