[llvm] [tools][llc] Add `--save-stats` option (PR #163967)

[Jon Roelofs via llvm-commits]

================
@@ -355,6 +366,50 @@ static std::unique_ptr<ToolOutputFile> GetOutputStream(const char *TargetName,
   return FDOut;
 }
 
+static int MaybeEnableStats() {
+  if (SaveStats.getNumOccurrences() > 0) {
+    if (SaveStats.empty() || SaveStats == "cwd" || SaveStats == "obj") {
+      llvm::EnableStatistics(false);
+    } else {
+      WithColor::error(errs(), "llc")
+          << "Invalid --save-stats value: " << SaveStats
+          << ", must be empty, 'cwd' or 'obj'\n";
+      return 1;
+    }
+  }
+  return 0;
+}
+
+static int MaybeSaveStats(std::string &&OutputFilename) {
+  if (SaveStats.getNumOccurrences() > 0) {
+    SmallString<128> StatsFilename;
+    if (SaveStats == "obj") {
+      StatsFilename = OutputFilename;
+      llvm::sys::path::remove_filename(StatsFilename);
+    } else {
+      assert((SaveStats.empty() || SaveStats == "cwd") &&
+             "Should have been a valid --save-stats value");
+    }
+
+    auto BaseName = llvm::sys::path::filename(OutputFilename);
+    llvm::sys::path::append(StatsFilename, BaseName);
+    llvm::sys::path::replace_extension(StatsFilename, "stats");
+
+    auto FileFlags = llvm::sys::fs::OF_TextWithCRLF;
+    std::error_code EC;
+    auto StatsOS =
+        std::make_unique<llvm::raw_fd_ostream>(StatsFilename, EC, FileFlags);
+    if (EC) {
+      WithColor::error(errs(), "llc")
+          << "Unable to open statistics file: " << EC.message() << "\n";
+      return 1;
+    } else {
+      llvm::PrintStatisticsJSON(*StatsOS);
+    }
----------------
jroelofs wrote:

no `else` after `return`
```suggestion
    }
    llvm::PrintStatisticsJSON(*StatsOS);
```

https://github.com/llvm/llvm-project/pull/163967