[PATCH] D94647: [Driver] -gsplit-dwarf: Produce .dwo regardless of -gN for -fthinlto-index=

[David Blaikie via Phabricator via cfe-commits]

dblaikie added inline comments.



Comment at: clang/lib/Driver/ToolChains/Clang.cpp:3758
+  // 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

inglorion wrote:
> tejohnson wrote:
> > MaskRay wrote:
> > > dblaikie wrote:
> > > > tejohnson wrote:
> > > > > Better to simply check if the input type is IR/BC via 
> > > > > types::isLLVMIR(Input.getType()). Technically you don't need ThinLTO 
> > > > > to do a clang compile with bitcode input. Looks like Input can be 
> > > > > passed down from the caller.
> > > > Good point! +1 to that.
> > > That currently does not work:
> > > `clang -g -c -flto a.c; fclang -gsplit-dwarf -g a.o -o a`
> > > there is no .dwo
> > I assume you mean clang and not "fclang"?
> > 
> > Try with "-x ir" like "clang -gsplit-dwarf -g -x ir a.o -o a". I thought 
> > that the -x ir was needed when passing a .o file that was actually bitcode?
> > I thought that the -x ir was needed when passing a .o file that was 
> > actually bitcode?
> 
> I think that's a linker invocation, not a codegen invocation.
> 
> I would have spelled it
> 
>   clang -fuse-ld=lld -flto -gsplit-dwarf -g a.o -o a
> 
> And, for me at least, it does use debug fission:
> 
>   objdump -g a | grep dwo
>   DW_AT_GNU_dwo_name DW_FORM_strp
>   DW_AT_GNU_dwo_id   DW_FORM_data8
>   <14>   DW_AT_GNU_dwo_name: (indirect string, offset: 0x29): a_dwo/0.dwo
>   <18>   DW_AT_GNU_dwo_id  : 0x24fab96c73f98143
> 0x0020 2f746d70 2f747374 00615f64 776f2f30 /tmp/tst.a_dwo/0
> 0x0030 2e64776f 00 .dwo.
> 
They're somewhat different things.
```
clang -gsplit-dwarf -g -x ir a.o -o a
```
With a single file, this is the same as the lto invocation - but with multiple 
files this is different, because it compiles the IR to object code, then links, 
rather than linking then compiling to object code.
The easier way to write "Compile to object code" includes things like:
```
clang -c -gsplit-dwarf a.bc
clang -c -gsplit-dwarf a.ll
```
for bitcode IR and textual IR respectively. 

But yes, all these forms, whatever user-driven invocation causes IR->object 
code generation to occur, should accept and respect -gsplit-dwarf. And I think 
hopefully that's the case after/with D94655


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[PATCH] D94647: [Driver] -gsplit-dwarf: Produce .dwo regardless of -gN for -fthinlto-index=

[Bob Haarman via Phabricator via cfe-commits]

inglorion added inline comments.



Comment at: clang/lib/Driver/ToolChains/Clang.cpp:3758
+  // 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

tejohnson wrote:
> MaskRay wrote:
> > dblaikie wrote:
> > > tejohnson wrote:
> > > > Better to simply check if the input type is IR/BC via 
> > > > types::isLLVMIR(Input.getType()). Technically you don't need ThinLTO to 
> > > > do a clang compile with bitcode input. Looks like Input can be passed 
> > > > down from the caller.
> > > Good point! +1 to that.
> > That currently does not work:
> > `clang -g -c -flto a.c; fclang -gsplit-dwarf -g a.o -o a`
> > there is no .dwo
> I assume you mean clang and not "fclang"?
> 
> Try with "-x ir" like "clang -gsplit-dwarf -g -x ir a.o -o a". I thought that 
> the -x ir was needed when passing a .o file that was actually bitcode?
> I thought that the -x ir was needed when passing a .o file that was actually 
> bitcode?

I think that's a linker invocation, not a codegen invocation.

I would have spelled it

  clang -fuse-ld=lld -flto -gsplit-dwarf -g a.o -o a

And, for me at least, it does use debug fission:

  objdump -g a | grep dwo
  DW_AT_GNU_dwo_name DW_FORM_strp
  DW_AT_GNU_dwo_id   DW_FORM_data8
  <14>   DW_AT_GNU_dwo_name: (indirect string, offset: 0x29): a_dwo/0.dwo
  <18>   DW_AT_GNU_dwo_id  : 0x24fab96c73f98143
0x0020 2f746d70 2f747374 00615f64 776f2f30 /tmp/tst.a_dwo/0
0x0030 2e64776f 00 .dwo.



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[PATCH] D94647: [Driver] -gsplit-dwarf: Produce .dwo regardless of -gN for -fthinlto-index=

[Fangrui Song via Phabricator via cfe-commits]

MaskRay added a comment.

In D94647#2499153 , @inglorion wrote:

> Can we not just make -gsplit-dwarf set the DwarfFissionKind without also 
> looking at other things? That way, we don't have to worry about detecting the 
> right mix of -g, -g2, -fthinlto-index, -x ir, bitcode input, etc. If there is 
> some reason why this doesn't work, I would also like it to be expressed in a 
> comment in the code so that someone doesn't come along and simplify/break the 
> code later on.

D94655 


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[PATCH] D94647: [Driver] -gsplit-dwarf: Produce .dwo regardless of -gN for -fthinlto-index=

[Bob Haarman via Phabricator via cfe-commits]

inglorion added a comment.

Can we not just make -gsplit-dwarf set the DwarfFissionKind without also 
looking at other things? That way, we don't have to worry about detecting the 
right mix of -g, -g2, -fthinlto-index, -x ir, bitcode input, etc. If there is 
some reason why this doesn't work, I would also like it to be expressed in a 
comment in the code so that someone doesn't come along and simplify/break the 
code later on.


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[PATCH] D94647: [Driver] -gsplit-dwarf: Produce .dwo regardless of -gN for -fthinlto-index=

[Teresa Johnson via Phabricator via cfe-commits]

tejohnson added inline comments.



Comment at: clang/lib/Driver/ToolChains/Clang.cpp:3758
+  // 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

MaskRay wrote:
> dblaikie wrote:
> > tejohnson wrote:
> > > Better to simply check if the input type is IR/BC via 
> > > types::isLLVMIR(Input.getType()). Technically you don't need ThinLTO to 
> > > do a clang compile with bitcode input. Looks like Input can be passed 
> > > down from the caller.
> > Good point! +1 to that.
> That currently does not work:
> `clang -g -c -flto a.c; fclang -gsplit-dwarf -g a.o -o a`
> there is no .dwo
I assume you mean clang and not "fclang"?

Try with "-x ir" like "clang -gsplit-dwarf -g -x ir a.o -o a". I thought that 
the -x ir was needed when passing a .o file that was actually bitcode?


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[PATCH] D94647: [Driver] -gsplit-dwarf: Produce .dwo regardless of -gN for -fthinlto-index=

[Fangrui Song via Phabricator via cfe-commits]

MaskRay added inline comments.



Comment at: clang/lib/Driver/ToolChains/Clang.cpp:3758
+  // 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

dblaikie wrote:
> tejohnson wrote:
> > Better to simply check if the input type is IR/BC via 
> > types::isLLVMIR(Input.getType()). Technically you don't need ThinLTO to do 
> > a clang compile with bitcode input. Looks like Input can be passed down 
> > from the caller.
> Good point! +1 to that.
That currently does not work:
`clang -g -c -flto a.c; fclang -gsplit-dwarf -g a.o -o a`
there is no .dwo


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[PATCH] D94647: [Driver] -gsplit-dwarf: Produce .dwo regardless of -gN for -fthinlto-index=

[David Blaikie via Phabricator via cfe-commits]

dblaikie added inline comments.



Comment at: clang/lib/Driver/ToolChains/Clang.cpp:3758
+  // 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

tejohnson wrote:
> Better to simply check if the input type is IR/BC via 
> types::isLLVMIR(Input.getType()). Technically you don't need ThinLTO to do a 
> clang compile with bitcode input. Looks like Input can be passed down from 
> the caller.
Good point! +1 to that.


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[PATCH] D94647: [Driver] -gsplit-dwarf: Produce .dwo regardless of -gN for -fthinlto-index=

[Teresa Johnson via Phabricator via cfe-commits]

tejohnson added inline comments.



Comment at: clang/lib/Driver/ToolChains/Clang.cpp:3758
+  // 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

Better to simply check if the input type is IR/BC via 
types::isLLVMIR(Input.getType()). Technically you don't need ThinLTO to do a 
clang compile with bitcode input. Looks like Input can be passed down from the 
caller.


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[PATCH] D94647: [Driver] -gsplit-dwarf: Produce .dwo regardless of -gN for -fthinlto-index=

[Fangrui Song via Phabricator via cfe-commits]

This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rG53b34601abf1: [Driver] -gsplit-dwarf: Produce .dwo 
regardless of -gN for -fthinlto-index= (authored by MaskRay).

Changed prior to commit:
  https://reviews.llvm.org/D94647?vs=316558=316563#toc

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Files:
  clang/lib/Driver/ToolChains/Clang.cpp
  clang/test/Driver/split-debug.c


Index: clang/test/Driver/split-debug.c
===
--- clang/test/Driver/split-debug.c
+++ 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
Index: clang/lib/Driver/ToolChains/Clang.cpp
===
--- clang/lib/Driver/ToolChains/Clang.cpp
+++ clang/lib/Driver/ToolChains/Clang.cpp
@@ -3754,7 +3754,12 @@
   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 @@
   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.


Index: clang/test/Driver/split-debug.c
===
--- clang/test/Driver/split-debug.c
+++ 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
Index: clang/lib/Driver/ToolChains/Clang.cpp
===
--- clang/lib/Driver/ToolChains/Clang.cpp
+++ clang/lib/Driver/ToolChains/Clang.cpp
@@ -3754,7 +3754,12 @@
   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 @@
   DwarfFission = DwarfFissionKind::None;
   SplitDWARFInlining = false;
 }
-
+  }
+  if (const Arg *A = Args.getLastArg(options::OPT_g_Group)) {
 DebugInfoKind = codegenoptions::LimitedDebugInfo;
 
 // If the last option explicitly 

[PATCH] D94647: [Driver] -gsplit-dwarf: Produce .dwo regardless of -gN if -fthinlto-index= is specified

[David Blaikie via Phabricator via cfe-commits]

dblaikie accepted this revision.
dblaikie added a comment.
This revision is now accepted and ready to land.

Looks alright. I wouldn't mind knowing a bit more about how these things 
interact if different types of input files are listed together in a single 
command line, though.


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[PATCH] D94647: [Driver] -gsplit-dwarf: Produce .dwo regardless of -gN if -fthinlto-index= is specified

[Fangrui Song via Phabricator via cfe-commits]

MaskRay added a comment.

In D94647#2497170 , @dblaikie wrote:

> In implicit thinlto this seemed to work for me without any changes:
>
>   $ clang++-tot -flto=thin test.cpp -g -c
>   $ clang++-tot -flto=thin -fuse-ld=lld -gsplit-dwarf test.o && 
> llvm-dwarfdump-tot a.out
>   a.out:  file format elf64-x86-64
>   
>   .debug_info contents:
>   0x: Compile Unit: length = 0x002c, format = DWARF32, version = 
> 0x0004, abbr_offset = 0x, addr_size = 0x08 (next unit at 0x0030)
>   
>   0x000b: DW_TAG_compile_unit
> DW_AT_stmt_list   (0x)
> DW_AT_comp_dir
> ("/usr/local/google/home/blaikie/dev/scratch")
> DW_AT_GNU_dwo_name("a.out_dwo/1.dwo")
> DW_AT_GNU_dwo_id  (0xf29563d7c812deae)
> DW_AT_low_pc  (0x00201730)
> DW_AT_high_pc (0x00201738)
> DW_AT_GNU_addr_base   (0x)
>
> Any idea why that worked without the need for a special case/changes? Might 
> be nice if both these use cases (implicit and explicit thinlto) somehow 
> managed to use more common code generation options. But I guess that's too 
> different - probably some generic "take all the clang flags and pass them 
> through to the linker to pass back to the compiler", which isn't really 
> relevant to this... well, maybe (if they're being passed back to the compiler 
> in implicit thin lto, how does implicit thin lto work correctly without the 
> -g flag?)

Interesting. D44788  let Clang driver pass 
`-plugin-opt=dwo_dir=` to the linker. LTOBackend.cpp emits 
`$dwo_dir/[1234].dwo`.

There are .dwo files but the file names are a bit less ideal. For distributed 
ThinLTO, I think specifying the dwo filename explicitly is better.


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[PATCH] D94647: [Driver] -gsplit-dwarf: Produce .dwo regardless of -gN if -fthinlto-index= is specified

[David Blaikie via Phabricator via cfe-commits]

dblaikie added a comment.

In implicit thinlto this seemed to work for me without any changes:

  $ clang++-tot -flto=thin test.cpp -g -c
  $ clang++-tot -flto=thin -fuse-ld=lld -gsplit-dwarf test.o && 
llvm-dwarfdump-tot a.out
  a.out:  file format elf64-x86-64
  
  .debug_info contents:
  0x: Compile Unit: length = 0x002c, format = DWARF32, version = 
0x0004, abbr_offset = 0x, addr_size = 0x08 (next unit at 0x0030)
  
  0x000b: DW_TAG_compile_unit
DW_AT_stmt_list   (0x)
DW_AT_comp_dir("/usr/local/google/home/blaikie/dev/scratch")
DW_AT_GNU_dwo_name("a.out_dwo/1.dwo")
DW_AT_GNU_dwo_id  (0xf29563d7c812deae)
DW_AT_low_pc  (0x00201730)
DW_AT_high_pc (0x00201738)
DW_AT_GNU_addr_base   (0x)

Any idea why that worked without the need for a special case/changes? Might be 
nice if both these use cases (implicit and explicit thinlto) somehow managed to 
use more common code generation options. But I guess that's too different - 
probably some generic "take all the clang flags and pass them through to the 
linker to pass back to the compiler", which isn't really relevant to this... 
well, maybe (if they're being passed back to the compiler in implicit thin lto, 
how does implicit thin lto work correctly without the -g flag?)


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[PATCH] D94647: [Driver] -gsplit-dwarf: Produce .dwo regardless of -gN if -fthinlto-index= is specified

[Fangrui Song via Phabricator via cfe-commits]

MaskRay updated this revision to Diff 316558.
MaskRay added a comment.

improve code comment


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Files:
  clang/lib/Driver/ToolChains/Clang.cpp
  clang/test/Driver/split-debug.c


Index: clang/test/Driver/split-debug.c
===
--- clang/test/Driver/split-debug.c
+++ 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
Index: clang/lib/Driver/ToolChains/Clang.cpp
===
--- clang/lib/Driver/ToolChains/Clang.cpp
+++ clang/lib/Driver/ToolChains/Clang.cpp
@@ -3754,7 +3754,12 @@
   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 -g. For -gsplit-dwarf in 
ThinLTO
+  // backend phase which does object file generation and no IR generation, -g
+  // should not be needed. So allow -gsplit-dwarf with either -g 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 @@
   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.


Index: clang/test/Driver/split-debug.c
===
--- clang/test/Driver/split-debug.c
+++ 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
Index: clang/lib/Driver/ToolChains/Clang.cpp
===
--- clang/lib/Driver/ToolChains/Clang.cpp
+++ clang/lib/Driver/ToolChains/Clang.cpp
@@ -3754,7 +3754,12 @@
   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 -g. For -gsplit-dwarf in ThinLTO
+  // backend phase which does object file generation and no IR generation, -g
+  // should not be needed. So allow -gsplit-dwarf with either -g 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 @@
   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.
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[PATCH] D94647: [Driver] -gsplit-dwarf: Produce .dwo regardless of -gN if -fthinlto-index= is specified

[Fangrui Song via Phabricator via cfe-commits]

MaskRay created this revision.
MaskRay added reviewers: dblaikie, inglorion, thakis.
Herald added a subscriber: arphaman.
MaskRay requested review of this revision.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.

-g is an IR generation option while -gsplit-dwarf is an object file generation 
option.
-gsplit-dwarf should not be needed for ThinLTO backend compile, which does 
object file generation.

`-fthinlto-index= -gsplit-dwarf` emits .dwo even in the absence of -g.
This should fix https://crbug.com/1158215

  // 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


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D94647

Files:
  clang/lib/Driver/ToolChains/Clang.cpp
  clang/test/Driver/split-debug.c


Index: clang/test/Driver/split-debug.c
===
--- clang/test/Driver/split-debug.c
+++ 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
Index: clang/lib/Driver/ToolChains/Clang.cpp
===
--- clang/lib/Driver/ToolChains/Clang.cpp
+++ clang/lib/Driver/ToolChains/Clang.cpp
@@ -3754,7 +3754,11 @@
   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 -g. -fthinlto-index= reads in
+  // bitcode files (which may be compiled with -g) and emits an object file.
+  // Allow -gsplit-dwarf with -fthinlto-index= as well.
+  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 +3766,8 @@
   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.


Index: clang/test/Driver/split-debug.c
===
--- clang/test/Driver/split-debug.c
+++ 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
Index: clang/lib/Driver/ToolChains/Clang.cpp
===
--- clang/lib/Driver/ToolChains/Clang.cpp
+++ clang/lib/Driver/ToolChains/Clang.cpp
@@ -3754,7 +3754,11 @@
   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 -g. -fthinlto-index= reads in
+  // bitcode files (which may be compiled with -g) and emits an object file.
+  // Allow -gsplit-dwarf with