[PATCH] D84565: [Darwin] [Driver] Clang should invoke dsymutil for lto builds -g*

[Daniel Sanders via Phabricator via cfe-commits]

dsanders added a comment.

In D84565#2173615 <https://reviews.llvm.org/D84565#2173615>, @JDevlieghere wrote:

> When you don’t pass any specific options to the linker, it’s going to generate a temporary `lto.o` file in `/tmp` and delete it after the link. When `dsymutil` will try to read that, it won't be there anymore. Unless I'm missing I don't think this is going to work. If it turns out I'm mistaken please add that situation as a test case.


Are you thinking of the `-Wl,-object_path_lto,path/foo-lto.o` code in AddLLVM.cmake where dsymutil is invoked after clang finishes? I'm using the same code path as this patch in https://reviews.llvm.org/D84127 using an empty source file to force ContainsCompileOrAssembleAction() to be true and get dsymutil to be invoked. When clang manages both the per-arch links and the dsymutil, the temporary objects get unique names (e.g. `-object_path_lto /var/folders/0s/8zdwsz0d1glcx6v1nc_nv5gw0000gn/T/cc-95f3fc.o`) and stick around until after dsymutil is invoked.



================
Comment at: clang/lib/Driver/Driver.cpp:2037
+    bool isGeneratingTemporaryObject =
+        ContainsCompileOrAssembleAction(Actions.back()) || LTOMode != LTOK_None;
     if ((enablesDebugInfo || willEmitRemarks(Args)) &&
----------------
This should fix the same issue as the workaround I was using in D84127.

I'm not entirely convinced that this is all of it though. It seems strange to me that these two scripts produce different build products (aside from ret0.o):
```
$ rm -rf external ret0 ret0.*
$ echo 'int main() { return 0; }' > ret0.c
$ use_cflags="--sysroot=$SYSROOT -g"
$ ../build/bin/clang -o ret0 ret0.c ${=use_cflags}
$ ls
ret0      ret0.c    ret0.dSYM
```
```
$ rm -rf external ret0 ret0.*
$ echo 'int main() { return 0; }' > ret0.c
$ use_cflags="--sysroot=$SYSROOT -g"
$ ../build/bin/clang -c -o ret0.o ret0.c ${=use_cflags}
$ ../build/bin/clang -o ret0 ret0.o ${=use_cflags}
$ ls
ret0   ret0.c ret0.o
```
I'd expect them to either consistently extract the dSYM or consistently lipo the slices together including the debug info. I don't have a strong opinion about which is right, it's just the inconsistency that's bothering me


Repository:
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https://reviews.llvm.org/D84565