[Driver] [Modules] Support -fmodule-output (1/2)

Patches to support the one-phase compilation model for modules.

The behavior:
(1) If -o and -c is specified , the module file is in the same path
within the same directory as the output the -o specified and with a new
suffix .pcm.
(2) Otherwise, the module file is in the same path within the working
directory directory with the name of the input file with a new suffix
.pcm

For example,

```
Hello.cppm Use.cpp
```

A trivial one and the contents are ignored. When we run:

```
clang++ -std=c++20 -fmodule-output Hello.cppm -c
```

The directory would look like:

```
Hello.cppm  Hello.o  Hello.pcm Use.cpp
```

And if we run:

```
clang++ -std=c++20 -fmodule-output Hello.cppm -c -o output/Hello.o
```

Then the `output` directory may look like:

```
Hello.o  Hello.pcm
```

Reviewed By: dblaikie, iains, tahonermann

Differential Revision: https://reviews.llvm.org/D137058

1 files changed, 36 insertions, 2 deletions

diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index fe9e9bb..bc70a92 100644
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -5553,6 +5553,30 @@ const char *Driver::CreateTempFile(Compilation &C, StringRef Prefix,
   return C.addTempFile(C.getArgs().MakeArgString(TmpName));
 }
 
+// Calculate the output path of the module file when compiling a module unit
+// with the `-fmodule-output` option specified. The behavior is:
+// - If the output object file of the module unit is specified, the output path
+//   of the module file should be the same with the output object file except
+//   the corresponding suffix. This requires both `-o` and `-c` are specified.
+// - Otherwise, the output path of the module file will be the same with the
+//   input with the corresponding suffix.
+static const char *GetModuleOutputPath(Compilation &C, const JobAction &JA,
+                                       const char *BaseInput) {
+  assert(isa<PrecompileJobAction>(JA) && JA.getType() == types::TY_ModuleFile &&
+         C.getArgs().hasArg(options::OPT_fmodule_output));
+
+  SmallString<64> OutputPath;
+  Arg *FinalOutput = C.getArgs().getLastArg(options::OPT_o);
+  if (FinalOutput && C.getArgs().hasArg(options::OPT_c))
+    OutputPath = FinalOutput->getValue();
+  else
+    OutputPath = BaseInput;
+
+  const char *Extension = types::getTypeTempSuffix(JA.getType());
+  llvm::sys::path::replace_extension(OutputPath, Extension);
+  return C.addResultFile(C.getArgs().MakeArgString(OutputPath.c_str()), &JA);
+}
+
 const char *Driver::GetNamedOutputPath(Compilation &C, const JobAction &JA,
                                        const char *BaseInput,
                                        StringRef OrigBoundArch, bool AtTopLevel,
@@ -5609,6 +5633,16 @@ const char *Driver::GetNamedOutputPath(Compilation &C, const JobAction &JA,
         &JA);
   }
 
+  if (MultipleArchs && C.getArgs().hasArg(options::OPT_fmodule_output))
+    Diag(clang::diag::err_drv_module_output_with_multiple_arch);
+
+  // If we're emitting a module output with the specified option
+  // `-fmodule-output`.
+  if (!AtTopLevel && isa<PrecompileJobAction>(JA) &&
+      JA.getType() == types::TY_ModuleFile &&
+      C.getArgs().hasArg(options::OPT_fmodule_output))
+    return GetModuleOutputPath(C, JA, BaseInput);
+
   // Output to a temporary file?
   if ((!AtTopLevel && !isSaveTempsEnabled() &&
        !C.getArgs().hasArg(options::OPT__SLASH_Fo)) ||
@@ -5771,9 +5805,9 @@ const char *Driver::GetNamedOutputPath(Compilation &C, const JobAction &JA,
     else
       llvm::sys::path::append(BasePath, NamedOutput);
     return C.addResultFile(C.getArgs().MakeArgString(BasePath.c_str()), &JA);
-  } else {
-    return C.addResultFile(NamedOutput, &JA);
   }
+
+  return C.addResultFile(NamedOutput, &JA);
 }
 
 std::string Driver::GetFilePath(StringRef Name, const ToolChain &TC) const {