| commit 53b34601abf1d48e8df210ab8127b16fd35e275a |
| Author: Fangrui Song <i@maskray.me> |
| Date: Wed Jan 13 21:01:53 2021 -0800 |
| |
| [Driver] -gsplit-dwarf: Produce .dwo regardless of -gN for -fthinlto-index= |
| |
| -g is an IR generation option while -gsplit-dwarf is an object file generation option. |
| For -gsplit-dwarf in the backend phase of a distributed ThinLTO (-fthinlto-index=) which does object file generation and no IR generation, -g should not be needed. |
| |
| This patch makes `-fthinlto-index= -gsplit-dwarf` emit .dwo even in the absence of -g. |
| This should fix https://crbug.com/1158215 after D80391. |
| |
| ``` |
| // Distributed ThinLTO usage |
| clang -g -O2 -c -flto=thin -fthin-link-bitcode=a.indexing.o a.c |
| clang -g -O2 -c -flto=thin -fthin-link-bitcode=b.indexing.o b.c |
| clang -fuse-ld=lld -Wl,--thinlto-index-only=a.rsp -Wl,--thinlto-prefix-replace=';lto/' -Wl,--thinlto-object-suffix-replace='.indexing.o;.o' a.indexing.o b.indexing.o |
| clang -gsplit-dwarf -O2 -c -fthinlto-index=lto/a.o.thinlto.bc a.o -o lto/a.o |
| clang -gsplit-dwarf -O2 -c -fthinlto-index=lto/b.o.thinlto.bc b.o -o lto/b.o |
| clang -fuse-ld=lld @a.rsp -o exe |
| ``` |
| |
| Note: for implicit regular/Thin LTO, .dwo emission works without this patch: |
| `clang -flto=thin -gsplit-dwarf a.o b.o` passes `-plugin-opt=dwo_dir=` to the linker. |
| The linker forwards the option to LTO. LTOBackend.cpp emits `$dwo_dir/[01234].dwo`. |
| |
| Reviewed By: dblaikie |
| |
| Differential Revision: https://reviews.llvm.org/D94647 |
| --- |
| clang/lib/Driver/ToolChains/Clang.cpp | 10 ++++++++-- |
| clang/test/Driver/split-debug.c | 8 ++++++++ |
| 2 files changed, 16 insertions(+), 2 deletions(-) |
| |
| diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp |
| index d83835a0f7b8..0c821b85c229 100644 |
| --- a/clang/lib/Driver/ToolChains/Clang.cpp |
| +++ b/clang/lib/Driver/ToolChains/Clang.cpp |
| @@ -3754,7 +3754,12 @@ static void RenderDebugOptions(const ToolChain &TC, const Driver &D, |
| Args.hasFlag(options::OPT_fsplit_dwarf_inlining, |
| options::OPT_fno_split_dwarf_inlining, false); |
| |
| - if (const Arg *A = Args.getLastArg(options::OPT_g_Group)) { |
| + // Normally -gsplit-dwarf is only useful with -gN. For -gsplit-dwarf in the |
| + // backend phase of a distributed ThinLTO which does object file generation |
| + // and no IR generation, -gN should not be needed. So allow -gsplit-dwarf with |
| + // either -gN or -fthinlto-index=. |
| + if (Args.hasArg(options::OPT_g_Group) || |
| + Args.hasArg(options::OPT_fthinlto_index_EQ)) { |
| Arg *SplitDWARFArg; |
| DwarfFission = getDebugFissionKind(D, Args, SplitDWARFArg); |
| if (DwarfFission != DwarfFissionKind::None && |
| @@ -3762,7 +3767,8 @@ static void RenderDebugOptions(const ToolChain &TC, const Driver &D, |
| DwarfFission = DwarfFissionKind::None; |
| SplitDWARFInlining = false; |
| } |
| - |
| + } |
| + if (const Arg *A = Args.getLastArg(options::OPT_g_Group)) { |
| DebugInfoKind = codegenoptions::LimitedDebugInfo; |
| |
| // If the last option explicitly specified a debug-info level, use it. |
| diff --git a/clang/test/Driver/split-debug.c b/clang/test/Driver/split-debug.c |
| index de1258dcb13c..2ce4ca980c3f 100644 |
| --- a/clang/test/Driver/split-debug.c |
| +++ b/clang/test/Driver/split-debug.c |
| @@ -24,6 +24,14 @@ |
| /// -gsplit-dwarf is a no-op if no -g is specified. |
| // RUN: %clang -### -c -target x86_64 -gsplit-dwarf %s 2>&1 | FileCheck %s --check-prefix=G0 |
| |
| +/// ... unless -fthinlto-index= is specified. |
| +// RUN: echo > %t.bc |
| +// RUN: %clang -### -c -target x86_64 -fthinlto-index=dummy -gsplit-dwarf %t.bc 2>&1 | FileCheck %s --check-prefix=THINLTO |
| + |
| +// THINLTO-NOT: "-debug-info-kind= |
| +// THINLTO: "-ggnu-pubnames" |
| +// THINLTO-SAME: "-split-dwarf-file" "{{.*}}.dwo" "-split-dwarf-output" "{{.*}}.dwo" |
| + |
| /// -gno-split-dwarf disables debug fission. |
| // RUN: %clang -### -c -target x86_64 -gsplit-dwarf -g -gno-split-dwarf %s 2>&1 | FileCheck %s --check-prefix=NOSPLIT |
| // RUN: %clang -### -c -target x86_64 -gsplit-dwarf=single -g -gno-split-dwarf %s 2>&1 | FileCheck %s --check-prefix=NOSPLIT |