[lld] [lld][COFF][LTO] Implement /lldemit:asm option (PR #67079)

[Matheus Izvekov via llvm-commits]

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@@ -235,20 +245,21 @@ std::vector<InputFile *> BitcodeCompiler::compile() {
     if (bitcodeFilePath == "ld-temp.o") {
       ltoObjName =
           saver().save(Twine(ctx.config.outputFile) + ".lto" +
-                       (i == 0 ? Twine("") : Twine('.') + Twine(i)) + ".obj");
+                       (i == 0 ? Twine("") : Twine('.') + Twine(i)) + Ext);
     } else {
       StringRef directory = sys::path::parent_path(bitcodeFilePath);
-      StringRef baseName = sys::path::filename(bitcodeFilePath);
+      StringRef baseName = sys::path::stem(bitcodeFilePath);
----------------
mizvekov wrote:

This is just for the emitASM / saveTemps case, so we don't end up appending `.asm` to whatever is the full output name.

Ie when generating temporaries, we would previously generate complicated and confusing file names here, for example:

`lld-link a.obj b.obj /output app.exe`
Would generate:
`app.exe.lto.a.obj`
`app.exe.lto.b.obj`

But if your inputs had a different, possibly even more accurate extension, you could end up with this example:

`lld-link a.bc b.bc /output app.exe`
Would generate:
`app.exe.lto.a.bc`
`app.exe.lto.b.bc`

Even though these saved temps are object files, not bitcode files.

If I hadn't used stem, we would get names like this:

`lld-link /lldemit:asm a.obj b.obj /output app.exe`
Would generate:
`app.exe.lto.a.obj.asm`
`app.exe.lto.b.obj.asm`

With `stem`, we get this instead:
`app.exe.lto.a.asm`
`app.exe.lto.bj.asm`

https://github.com/llvm/llvm-project/pull/67079