Add support for LTO plugin option obj-path

[rdhindsa]

Summary

Add support for LTO plugin option obj-path

[pcc]

lld/ELF/LTO.cpp

282 ↗

(On Diff #145768)

You don't need this part any more. With thinlto-index-only, the obj-path file is not a "temporary" file but rather one of the final outputs.

302–307 ↗

(On Diff #145768)

I'd drop this part. We only need to support obj-path with thinlto-index-only.

[pcc]

lld/ELF/LTO.cpp

283 ↗

(On Diff #145777)

I wouldn't save the buffer at all if obj-path is not passed.

[rdhindsa]

lld/ELF/LTO.cpp

283 ↗

(On Diff #145777)

Wouldn't we want to store the generated file, if obj-path is not passed? Since we know that Buff[0] is not empty, aren't we supposed to store the content? In that case, is obj-path a requirement for thinlto-index-only?

[pcc]

lld/ELF/LTO.cpp

283 ↗

(On Diff #145777)

If you happen to know that all input files do not use full LTO then there is no need to pass obj-path. The linker shouldn't write a file to an arbitrary location in that case.

[rdhindsa]

Removed the test which ensured that regular LTO file was written with index only option. It needs to have obj-path option to write that file.

[pcc]

LGTM

[ruiu]

Please consider splitting "thinlto.ll" test file as it contains all tests for thinlto, and that's not desirabl, as small test files are more manageable than one large test file.

ELF/Config.h

struct Configuration {
   llvm::StringRef Chroot;
   llvm::StringRef DynamicLinker;
   llvm::StringRef Entry;
   llvm::StringRef Emulation;
   llvm::StringRef Fini;
   llvm::StringRef Init;
   llvm::StringRef LTOAAPipeline;
   llvm::StringRef LTONewPmPasses;
+  llvm::StringRef LTOObjPath;
   llvm::StringRef LTOSampleProfile;
   llvm::StringRef MapFile;
   llvm::StringRef OutputFile;
   llvm::StringRef OptRemarksFilename;
   llvm::StringRef ProgName;
   llvm::StringRef SoName;
   llvm::StringRef Sysroot;
   llvm::StringRef ThinLTOCacheDir;

ELF/Driver.cpp

for (auto *Arg : Args.filtered(OPT_plugin_opt)) {
     } else if (S.startswith("mcpu=")) {
       parseClangOption(Saver.save("-" + S), Arg->getSpelling());
     } else if (S == "new-pass-manager") {
       Config->LTONewPassManager = true;
     } else if (S == "debug-pass-manager") {
       Config->LTODebugPassManager = true;
     } else if (S.startswith("sample-profile=")) {
       Config->LTOSampleProfile = S.substr(15);
+    } else if (S.startswith("obj-path=")) {
+      Config->LTOObjPath = S.substr(9);
     } else if (S == "thinlto-index-only") {
       Config->ThinLTOIndexOnly = true;
     } else if (S.startswith("thinlto-index-only=")) {
       Config->ThinLTOIndexOnly = true;
       Config->ThinLTOIndexOnlyArg = S.substr(19);
     } else if (S == "thinlto-emit-imports-files") {
       Config->ThinLTOEmitImportsFiles = true;
     } else if (S.startswith("thinlto-prefix-replace=")) {

ELF/LTO.cpp

for (LazyObjFile *F : LazyObjFiles) {
       ModuleSummaryIndex M(false);
       M.setSkipModuleByDistributedBackend();
       WriteIndexToFile(M, *OS);
 
       if (Config->ThinLTOEmitImportsFiles)
         openFile(Path + ".imports");
     }
 
-    if (Config->SaveTemps)
-      saveBuffer(Buff[0], Config->OutputFile + ".lto.o");
+    if (!Config->LTOObjPath.empty())
+      saveBuffer(Buff[0], Config->LTOObjPath);
 
     // ThinLTO with index only option is required to generate only the index
     // files. After that, we exit from linker and ThinLTO backend runs in a
     // distributed environment.
     if (IndexFile)
       IndexFile->close();
     return {};
   }

test/ELF/lto/thinlto.ll

 ; RUN: rm -f %t.o.thinlto.bc
 ; RUN: rm -f %t2.o.thinlto.bc
 ; RUN: rm -f %t4.o.thinlto.bc
 ; RUN: ld.lld -m elf_x86_64 -shared %t.o %t2.o %t4.o -o %t5
 ; RUN: not ls %t.o.thinlto.bc
 ; RUN: not ls %t2.o.thinlto.bc
 ; RUN: not ls %t4.o.thinlto.bc
 
-; Ensure lld generates one regular LTO file via splitting for ThinLTO builds
-; RUN: rm -f %t.lto.o
-; RUN: ld.lld -save-temps --plugin-opt=thinlto-index-only -shared %t.o %t2.o -o %t
-; RUN: llvm-readobj -h %t.lto.o | FileCheck %s --check-prefix=FORMAT
-
 ; First force single-threaded mode
 ; RUN: rm -f %t.lto.o %t1.lto.o
 ; RUN: ld.lld -save-temps --thinlto-jobs=1 -shared %t.o %t2.o -o %t
 ; RUN: llvm-nm %t1.lto.o | FileCheck %s --check-prefix=NM1
 ; RUN: llvm-nm %t2.lto.o | FileCheck %s --check-prefix=NM2
 
 ; Next force multi-threaded mode
 ; RUN: rm -f %t2.lto.o %t21.lto.o
 ; RUN: ld.lld -save-temps --thinlto-jobs=2 -shared %t.o %t2.o -o %t2
 ; RUN: llvm-nm %t21.lto.o | FileCheck %s --check-prefix=NM1
 ; RUN: llvm-nm %t22.lto.o | FileCheck %s --check-prefix=NM2
 
 ; Then check without --thinlto-jobs (which currently default to hardware_concurrency)
 ; We just check that we don't crash or fail (as it's not sure which tests are
 ; stable on the final output file itself.
 ; RUN: ld.lld -shared %t.o %t2.o -o %t2
 
+; Test to ensure that thinlto-index-only with obj-path creates the file.
+; RUN: rm -f %t5.o
+; RUN: ld.lld --plugin-opt=thinlto-index-only --plugin-opt=obj-path=%t5.o -shared %t.o %t2.o -o %t4
+; RUN: llvm-readobj -h %t5.o | FileCheck %s --check-prefix=FORMAT
+; RUN: llvm-nm %t5.o | count 0
+
 ; NM: T f
 ; NM1: T f
 ; NM1-NOT: U g
 ; NM2: T g
 ; FORMAT: Format: ELF64-x86-64
 
 ; The backend index for this module contains summaries from itself and
 ; Inputs/thinlto.ll, as it imports from the latter.