[clang] [flang] [flang][debug] Add compressed DWARF support in Flang (PR #212584)
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Tue Jul 28 11:53:48 PDT 2026
https://github.com/timsmith78 created https://github.com/llvm/llvm-project/pull/212584
Re-use most of the clang implementation for compressed DWARF support in flang.
AI attribution: Co-developed with Claude Opus 4.6
>From b3d51382bd8fe6ef5842fb581747494f9ade87fd Mon Sep 17 00:00:00 2001
From: Timothy Smith <timothy.smith at hpe.com>
Date: Tue, 14 Jul 2026 15:23:40 -0500
Subject: [PATCH] [flang][debug] Add compressed DWARF support in Flang
Re-use most of the clang implementation for compressed DWARF support
in flang.
AI attribution: Co-developed with Claude Opus 4.6
---
clang/include/clang/Driver/CommonArgs.h | 4 +++
clang/include/clang/Options/Options.td | 17 ++++++++-
clang/lib/Driver/ToolChains/Clang.cpp | 36 ++-----------------
clang/lib/Driver/ToolChains/CommonArgs.cpp | 32 +++++++++++++++++
clang/lib/Driver/ToolChains/Flang.cpp | 5 +++
flang/docs/ReleaseNotes.md | 7 ++++
.../include/flang/Frontend/CodeGenOptions.def | 2 ++
flang/include/flang/Frontend/CodeGenOptions.h | 1 +
flang/lib/Frontend/CompilerInvocation.cpp | 17 +++++++++
flang/lib/Frontend/FrontendActions.cpp | 2 ++
.../Driver/compress-debug-sections-zstd.f90 | 9 +++++
flang/test/Driver/compress-debug-sections.f90 | 20 +++++++++++
.../Integration/debug-compressed-sections.f90 | 25 +++++++++++++
13 files changed, 142 insertions(+), 35 deletions(-)
create mode 100644 flang/test/Driver/compress-debug-sections-zstd.f90
create mode 100644 flang/test/Driver/compress-debug-sections.f90
create mode 100644 flang/test/Integration/debug-compressed-sections.f90
diff --git a/clang/include/clang/Driver/CommonArgs.h b/clang/include/clang/Driver/CommonArgs.h
index 8c861df793311..01e358a1d0717 100644
--- a/clang/include/clang/Driver/CommonArgs.h
+++ b/clang/include/clang/Driver/CommonArgs.h
@@ -50,6 +50,10 @@ void addLinkerCompressDebugSectionsOption(const ToolChain &TC,
const llvm::opt::ArgList &Args,
llvm::opt::ArgStringList &CmdArgs);
+void renderDebugInfoCompressionArgs(const llvm::opt::ArgList &Args,
+ llvm::opt::ArgStringList &CmdArgs,
+ const Driver &D, const ToolChain &TC);
+
void claimNoWarnArgs(const llvm::opt::ArgList &Args);
bool addSanitizerRuntimes(const ToolChain &TC, const llvm::opt::ArgList &Args,
diff --git a/clang/include/clang/Options/Options.td b/clang/include/clang/Options/Options.td
index 1478624265f79..d0a11115e7e05 100644
--- a/clang/include/clang/Options/Options.td
+++ b/clang/include/clang/Options/Options.td
@@ -5307,8 +5307,10 @@ def gmodules : Flag <["-"], "gmodules">, Group<gN_Group>,
" or precompiled headers">;
def gno_modules : Flag <["-"], "gno-modules">, Group<g_flags_Group>;
def gz_EQ : Joined<["-"], "gz=">, Group<g_flags_Group>,
+ Visibility<[ClangOption, FlangOption]>,
HelpText<"DWARF debug sections compression type">;
-def gz : Flag<["-"], "gz">, Alias<gz_EQ>, AliasArgs<["zlib"]>, Group<g_flags_Group>;
+def gz : Flag<["-"], "gz">, Alias<gz_EQ>, AliasArgs<["zlib"]>,
+ Visibility<[ClangOption, FlangOption]>, Group<g_flags_Group>;
def gembed_source : Flag<["-"], "gembed-source">, Group<g_flags_Group>,
Visibility<[ClangOption, CC1Option]>,
HelpText<"Embed source text in DWARF debug sections">,
@@ -7969,12 +7971,25 @@ def debugger_tuning_EQ : Joined<["-"], "debugger-tuning=">,
Values<"gdb,lldb,sce,dbx">,
NormalizedValuesScope<"llvm::DebuggerKind">, NormalizedValues<["GDB", "LLDB", "SCE", "DBX"]>,
MarshallingInfoEnum<CodeGenOpts<"DebuggerTuning">, "Default">;
+} // let Visibility = [CC1Option, CC1AsOption]
+
+// FC1Option: flang accepts --compress-debug-sections= but does not use
+// MarshallingInfoEnum for parsing. Flang hand-parses this option in
+// flang/lib/Frontend/CompilerInvocation.cpp (parseDebugArgs). The marshalling
+// metadata below is only used by clang's cc1 auto-generated parsing.
+let Visibility = [CC1Option, CC1AsOption, FC1Option] in {
+
def compress_debug_sections_EQ : Joined<["-", "--"], "compress-debug-sections=">,
HelpText<"DWARF debug sections compression type">, Values<"none,zlib,zstd">,
NormalizedValuesScope<"llvm::DebugCompressionType">, NormalizedValues<["None", "Zlib", "Zstd"]>,
MarshallingInfoEnum<CodeGenOpts<"CompressDebugSections">, "None">;
def compress_debug_sections : Flag<["-", "--"], "compress-debug-sections">,
Alias<compress_debug_sections_EQ>, AliasArgs<["zlib"]>;
+
+} // let Visibility = [CC1Option, CC1AsOption, FC1Option]
+
+let Visibility = [CC1Option, CC1AsOption] in {
+
def mno_exec_stack : Flag<["-"], "mnoexecstack">,
HelpText<"Mark the file as not needing an executable stack">,
MarshallingInfoFlag<CodeGenOpts<"NoExecStack">>;
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 94f9a26aac39f..c4a07940981b8 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -731,38 +731,6 @@ RenderDebugEnablingArgs(const ArgList &Args, ArgStringList &CmdArgs,
}
}
-static void RenderDebugInfoCompressionArgs(const ArgList &Args,
- ArgStringList &CmdArgs,
- const Driver &D,
- const ToolChain &TC) {
- const Arg *A = Args.getLastArg(options::OPT_gz_EQ);
- if (!A)
- return;
- if (checkDebugInfoOption(A, Args, D, TC)) {
- StringRef Value = A->getValue();
- if (Value == "none") {
- CmdArgs.push_back("--compress-debug-sections=none");
- } else if (Value == "zlib") {
- if (llvm::compression::zlib::isAvailable()) {
- CmdArgs.push_back(
- Args.MakeArgString("--compress-debug-sections=" + Twine(Value)));
- } else {
- D.Diag(diag::warn_debug_compression_unavailable) << "zlib";
- }
- } else if (Value == "zstd") {
- if (llvm::compression::zstd::isAvailable()) {
- CmdArgs.push_back(
- Args.MakeArgString("--compress-debug-sections=" + Twine(Value)));
- } else {
- D.Diag(diag::warn_debug_compression_unavailable) << "zstd";
- }
- } else {
- D.Diag(diag::err_drv_unsupported_option_argument)
- << A->getSpelling() << Value;
- }
- }
-}
-
static void handleAMDGPUCodeObjectVersionOptions(const Driver &D,
const ArgList &Args,
ArgStringList &CmdArgs,
@@ -5034,7 +5002,7 @@ renderDebugOptions(const ToolChain &TC, const Driver &D, const llvm::Triple &T,
CmdArgs.push_back("-dwarf-explicit-import");
renderDwarfFormat(D, T, Args, CmdArgs, EffectiveDWARFVersion);
- RenderDebugInfoCompressionArgs(Args, CmdArgs, D, TC);
+ renderDebugInfoCompressionArgs(Args, CmdArgs, D, TC);
// This controls whether or not we perform JustMyCode instrumentation.
if (Args.hasFlag(options::OPT_fjmc, options::OPT_fno_jmc, false)) {
@@ -9353,7 +9321,7 @@ void ClangAs::ConstructJob(Compilation &C, const JobAction &JA,
RenderDebugEnablingArgs(Args, CmdArgs, DebugInfoKind, DwarfVersion,
llvm::DebuggerKind::Default);
renderDwarfFormat(D, Triple, Args, CmdArgs, DwarfVersion);
- RenderDebugInfoCompressionArgs(Args, CmdArgs, D, getToolChain());
+ renderDebugInfoCompressionArgs(Args, CmdArgs, D, getToolChain());
// Handle -fPIC et al -- the relocation-model affects the assembler
// for some targets.
diff --git a/clang/lib/Driver/ToolChains/CommonArgs.cpp b/clang/lib/Driver/ToolChains/CommonArgs.cpp
index 08c06951cf220..a8b905bbe48c9 100644
--- a/clang/lib/Driver/ToolChains/CommonArgs.cpp
+++ b/clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -684,6 +684,38 @@ void tools::addLinkerCompressDebugSectionsOption(
}
}
+void tools::renderDebugInfoCompressionArgs(const ArgList &Args,
+ ArgStringList &CmdArgs,
+ const Driver &D,
+ const ToolChain &TC) {
+ const Arg *A = Args.getLastArg(options::OPT_gz_EQ);
+ if (!A)
+ return;
+ if (checkDebugInfoOption(A, Args, D, TC)) {
+ StringRef Value = A->getValue();
+ if (Value == "none") {
+ CmdArgs.push_back("--compress-debug-sections=none");
+ } else if (Value == "zlib") {
+ if (llvm::compression::zlib::isAvailable()) {
+ CmdArgs.push_back(
+ Args.MakeArgString("--compress-debug-sections=" + Twine(Value)));
+ } else {
+ D.Diag(diag::warn_debug_compression_unavailable) << "zlib";
+ }
+ } else if (Value == "zstd") {
+ if (llvm::compression::zstd::isAvailable()) {
+ CmdArgs.push_back(
+ Args.MakeArgString("--compress-debug-sections=" + Twine(Value)));
+ } else {
+ D.Diag(diag::warn_debug_compression_unavailable) << "zstd";
+ }
+ } else {
+ D.Diag(diag::err_drv_unsupported_option_argument)
+ << A->getSpelling() << Value;
+ }
+ }
+}
+
void tools::AddTargetFeature(const ArgList &Args,
std::vector<StringRef> &Features,
OptSpecifier OnOpt, OptSpecifier OffOpt,
diff --git a/clang/lib/Driver/ToolChains/Flang.cpp b/clang/lib/Driver/ToolChains/Flang.cpp
index 650148de1374a..aadc626d1c1ec 100644
--- a/clang/lib/Driver/ToolChains/Flang.cpp
+++ b/clang/lib/Driver/ToolChains/Flang.cpp
@@ -15,6 +15,7 @@
#include "clang/Options/OptionUtils.h"
#include "clang/Options/Options.h"
#include "llvm/Frontend/Debug/Options.h"
+#include "llvm/Support/Compression.h"
#include "llvm/Support/Path.h"
#include "llvm/TargetParser/Host.h"
#include "llvm/TargetParser/RISCVISAInfo.h"
@@ -199,6 +200,10 @@ void Flang::addDebugOptions(const llvm::opt::ArgList &Args, const JobAction &JA,
CmdArgs.push_back(SplitDWARFOut);
}
}
+
+ // Handle compressed debug sections (-gz).
+ renderDebugInfoCompressionArgs(Args, CmdArgs, D, TC);
+
addDebugInfoForProfilingArgs(D, TC, Args, CmdArgs);
}
diff --git a/flang/docs/ReleaseNotes.md b/flang/docs/ReleaseNotes.md
index 888da4d58b868..a2417b508f715 100644
--- a/flang/docs/ReleaseNotes.md
+++ b/flang/docs/ReleaseNotes.md
@@ -33,8 +33,15 @@ page](https://llvm.org/releases/).
## Non-comprehensive list of changes in this release
+- Added support for compressed DWARF debug sections. Flang now supports
+ compressing DWARF debug info in ELF object files using zlib or zstd,
+ reducing debug information size in compiled binaries.
+
## New Compiler Flags
+- Added `-gz` and `-gz=<format>` flags to enable compression of DWARF debug
+ sections. Supported formats are `zlib`, `zstd`, and `none`.
+
## Windows Support
## Fortran Language Changes in Flang
diff --git a/flang/include/flang/Frontend/CodeGenOptions.def b/flang/include/flang/Frontend/CodeGenOptions.def
index 53ddc20a6e810..d49a7f3647eec 100644
--- a/flang/include/flang/Frontend/CodeGenOptions.def
+++ b/flang/include/flang/Frontend/CodeGenOptions.def
@@ -71,5 +71,7 @@ ENUM_CODEGENOPT(ComplexRange, ComplexRangeKind, 3, ComplexRangeKind::CX_Full) //
ENUM_CODEGENOPT(DoConcurrentMapping, DoConcurrentMappingKind, 2, DoConcurrentMappingKind::DCMK_None) ///< Map `do concurrent` to OpenMP
+ENUM_CODEGENOPT(CompressDebugSections, llvm::DebugCompressionType, 2, llvm::DebugCompressionType::None) ///< DWARF debug sections compression type
+
#undef CODEGENOPT
#undef ENUM_CODEGENOPT
diff --git a/flang/include/flang/Frontend/CodeGenOptions.h b/flang/include/flang/Frontend/CodeGenOptions.h
index 257d7ca9c407d..68aa2b1810abf 100644
--- a/flang/include/flang/Frontend/CodeGenOptions.h
+++ b/flang/include/flang/Frontend/CodeGenOptions.h
@@ -20,6 +20,7 @@
#include "llvm/Frontend/Debug/Options.h"
#include "llvm/Frontend/Driver/CodeGenOptions.h"
#include "llvm/Support/CodeGen.h"
+#include "llvm/Support/Compression.h"
#include "llvm/Support/Regex.h"
#include "llvm/Target/TargetOptions.h"
#include <memory>
diff --git a/flang/lib/Frontend/CompilerInvocation.cpp b/flang/lib/Frontend/CompilerInvocation.cpp
index 79ad08353b64c..a925ef696133a 100644
--- a/flang/lib/Frontend/CompilerInvocation.cpp
+++ b/flang/lib/Frontend/CompilerInvocation.cpp
@@ -174,6 +174,23 @@ static bool parseDebugArgs(Fortran::frontend::CodeGenOptions &opts,
opts.DebugInfoForProfiling =
args.hasArg(clang::options::OPT_fdebug_info_for_profiling);
+ if (const llvm::opt::Arg *a =
+ args.getLastArg(clang::options::OPT_compress_debug_sections_EQ)) {
+ auto type = llvm::StringSwitch<std::optional<llvm::DebugCompressionType>>(
+ a->getValue())
+ .Case("none", llvm::DebugCompressionType::None)
+ .Case("zlib", llvm::DebugCompressionType::Zlib)
+ .Case("zstd", llvm::DebugCompressionType::Zstd)
+ .Default(std::nullopt);
+ if (type) {
+ opts.setCompressDebugSections(*type);
+ } else {
+ diags.Report(clang::diag::err_drv_invalid_value)
+ << a->getAsString(args) << a->getValue();
+ return false;
+ }
+ }
+
return true;
}
diff --git a/flang/lib/Frontend/FrontendActions.cpp b/flang/lib/Frontend/FrontendActions.cpp
index 428002f68578b..8955a8f61e513 100644
--- a/flang/lib/Frontend/FrontendActions.cpp
+++ b/flang/lib/Frontend/FrontendActions.cpp
@@ -1422,6 +1422,8 @@ void CodeGenAction::executeAction() {
targetMachine.Options.MCOptions.AsmVerbose = targetOpts.asmVerbose;
targetMachine.Options.MCOptions.SplitDwarfFile = codeGenOpts.SplitDwarfFile;
+ targetMachine.Options.MCOptions.CompressDebugSections =
+ codeGenOpts.getCompressDebugSections();
const llvm::Triple &theTriple = targetMachine.getTargetTriple();
diff --git a/flang/test/Driver/compress-debug-sections-zstd.f90 b/flang/test/Driver/compress-debug-sections-zstd.f90
new file mode 100644
index 0000000000000..530319a97ae23
--- /dev/null
+++ b/flang/test/Driver/compress-debug-sections-zstd.f90
@@ -0,0 +1,9 @@
+! Test -gz=zstd (compressed debug sections with zstd) option handling.
+
+! REQUIRES: zstd
+
+! RUN: %flang -### -c -target x86_64-unknown-linux-gnu -gz=zstd %s 2>&1 | FileCheck %s --check-prefix=GZ-ZSTD
+! GZ-ZSTD: "--compress-debug-sections=zstd"
+
+program test
+end program test
diff --git a/flang/test/Driver/compress-debug-sections.f90 b/flang/test/Driver/compress-debug-sections.f90
new file mode 100644
index 0000000000000..bce2001084ba2
--- /dev/null
+++ b/flang/test/Driver/compress-debug-sections.f90
@@ -0,0 +1,20 @@
+! Test -gz (compressed debug sections) option handling.
+
+! REQUIRES: zlib
+
+! RUN: %flang -### -c -target x86_64-unknown-linux-gnu -gz %s 2>&1 | FileCheck %s --check-prefix=GZ
+! RUN: %flang -### -c -target x86_64-unknown-linux-gnu -gz=zlib %s 2>&1 | FileCheck %s --check-prefix=GZ
+! GZ: "--compress-debug-sections=zlib"
+
+! RUN: %flang -### -c -target x86_64-unknown-linux-gnu -gz=none %s 2>&1 | FileCheck %s --check-prefix=GZ-NONE
+! GZ-NONE: "--compress-debug-sections=none"
+
+! RUN: not %flang -### -c -target x86_64-unknown-linux-gnu -gz=invalid %s 2>&1 | FileCheck %s --check-prefix=GZ-INVALID
+! GZ-INVALID: error: unsupported argument 'invalid' to option '-gz='
+
+! Test that -gz without -g still passes --compress-debug-sections to fc1.
+! RUN: %flang -### -c -target x86_64-unknown-linux-gnu -gz=zlib %s 2>&1 | FileCheck %s --check-prefix=GZ-NO-G
+! GZ-NO-G: "--compress-debug-sections=zlib"
+
+program test
+end program test
diff --git a/flang/test/Integration/debug-compressed-sections.f90 b/flang/test/Integration/debug-compressed-sections.f90
new file mode 100644
index 0000000000000..aac86f46df0f8
--- /dev/null
+++ b/flang/test/Integration/debug-compressed-sections.f90
@@ -0,0 +1,25 @@
+! REQUIRES: x86-registered-target, zlib
+
+! Test that --compress-debug-sections=zlib compresses debug sections in the
+! output object file.
+! RUN: %flang_fc1 -debug-info-kind=standalone -triple x86_64-unknown-linux \
+! RUN: --compress-debug-sections=zlib -emit-obj -o %t.o %s
+! RUN: llvm-readobj -S %t.o | FileCheck --check-prefix=ZLIB %s
+
+! ZLIB: Name: .debug_info
+! ZLIB: SHF_COMPRESSED
+
+! Test that --compress-debug-sections=none does not compress debug sections.
+! RUN: %flang_fc1 -debug-info-kind=standalone -triple x86_64-unknown-linux \
+! RUN: --compress-debug-sections=none -emit-obj -o %t_none.o %s
+! RUN: llvm-readobj -S %t_none.o | FileCheck --check-prefix=NONE %s
+
+! NONE: Name: .debug_info
+! NONE: Flags [
+! NONE-NOT: SHF_COMPRESSED
+
+program test
+ implicit none
+ integer :: x
+ x = 1
+end program test
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