[Driver] Use the output filename as the base name in getStatsFileName when -save-stats=obj

[dtcxzyw]

Summary

When linking a multi-file program with -save-stats=obj, clang will save internal statistics during the link-time code generation to <obj_dir>/xxx.stats where xxx is the first filename of inputs. This behavior is strange. Additionally, naming conflicts will occur when multiple binaries placed in the same directory depend on the same input (e.g., https://github.com/martinus/map_benchmark).
This patch uses the output filename as the base name instead of the first input when -save-stats=obj.

[dtcxzyw]

Fix test errors.

[dtcxzyw]

Add tests

[MaskRay]

-save-stats=obj behavior seems strange. I think we should port https://maskray.me/blog/2023-04-25-compiler-output-files to -save-stats and deprecated -save-stats=obj.

[MaskRay]

In D146364#4496131, @MaskRay wrote:

-save-stats=obj behavior seems strange. I think we should port https://maskray.me/blog/2023-04-25-compiler-output-files to -save-stats and deprecated -save-stats=obj.

I've added "fix -save-stats=obj" to my todo list for the https://maskray.me/blog/2023-04-25-compiler-output-files work I have been doing.

clang/lib/Driver/ToolChains/CommonArgs.cpp

SmallString<128> tools::getStatsFileName(const llvm::opt::ArgList &Args,
   if (!A && !D.CCPrintInternalStats)
     return {};
 
   SmallString<128> StatsFile;
   if (A) {
     StringRef SaveStats = A->getValue();
     if (SaveStats == "obj" && Output.isFilename()) {
       StatsFile.assign(Output.getFilename());
-      llvm::sys::path::remove_filename(StatsFile);
-    } else if (SaveStats != "cwd") {
+    } else if (SaveStats == "cwd") {
+      StatsFile.assign(llvm::sys::path::filename(Input.getBaseInput()));
+    } else {
       D.Diag(diag::err_drv_invalid_value) << A->getAsString(Args) << SaveStats;
       return {};
     }
 
-    StringRef BaseName = llvm::sys::path::filename(Input.getBaseInput());
-    llvm::sys::path::append(StatsFile, BaseName);
     llvm::sys::path::replace_extension(StatsFile, "stats");
   } else {
     assert(D.CCPrintInternalStats);
     StatsFile.assign(D.CCPrintInternalStatReportFilename.empty()
                          ? "-"
                          : D.CCPrintInternalStatReportFilename);
   }
   return StatsFile;