[llvm] [MC] Introduce ability to add target specific AsmStreamer (PR #107415)

[via llvm-commits]

https://github.com/tltao created https://github.com/llvm/llvm-project/pull/107415

Currently the AsmStreamer class `MCAsmStreamer.cpp` only outputs GNU assembly syntax. However, we wish to add additional AsmStreamer classes for specific targets that can output alternative assembly syntaxes (the immediate use case is HLASM syntax for z/OS).

This is the first patch to add this ability by utilizing the TargetRegistry functions. 

>From e7f0b5b8bbe34500b243bedbba97b447e741cc5a Mon Sep 17 00:00:00 2001
From: Tony Tao <tonytao at ca.ibm.com>
Date: Thu, 5 Sep 2024 11:13:00 -0400
Subject: [PATCH] Introduce ability to add target specific AsmStreamer

---
 llvm/include/llvm/MC/TargetRegistry.h | 12 ++++++++++++
 llvm/lib/MC/TargetRegistry.cpp        | 10 ++++++++--
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/llvm/include/llvm/MC/TargetRegistry.h b/llvm/include/llvm/MC/TargetRegistry.h
index 42d510c17bce39..1850139ba81491 100644
--- a/llvm/include/llvm/MC/TargetRegistry.h
+++ b/llvm/include/llvm/MC/TargetRegistry.h
@@ -208,6 +208,10 @@ class Target {
   using AsmTargetStreamerCtorTy =
       MCTargetStreamer *(*)(MCStreamer &S, formatted_raw_ostream &OS,
                             MCInstPrinter *InstPrint);
+  using AsmStreamerCtorTy =
+      MCStreamer *(*)(MCContext &Ctx, std::unique_ptr<formatted_raw_ostream> OS,
+                      MCInstPrinter *IP, std::unique_ptr<MCCodeEmitter> CE,
+                      std::unique_ptr<MCAsmBackend> TAB);
   using ObjectTargetStreamerCtorTy = MCTargetStreamer *(*)(
       MCStreamer &S, const MCSubtargetInfo &STI);
   using MCRelocationInfoCtorTy = MCRelocationInfo *(*)(const Triple &TT,
@@ -316,6 +320,10 @@ class Target {
   /// registered (default = nullptr).
   AsmTargetStreamerCtorTy AsmTargetStreamerCtorFn = nullptr;
 
+  /// Construction function for this target's AsmStreamer, if
+  /// registered (default = nullptr).
+  AsmStreamerCtorTy AsmStreamerCtorFn = nullptr;
+
   /// Construction function for this target's obj TargetStreamer, if
   /// registered (default = nullptr).
   ObjectTargetStreamerCtorTy ObjectTargetStreamerCtorFn = nullptr;
@@ -927,6 +935,10 @@ struct TargetRegistry {
     T.NullTargetStreamerCtorFn = Fn;
   }
 
+  static void RegisterAsmStreamer(Target &T, Target::AsmStreamerCtorTy Fn) {
+    T.AsmStreamerCtorFn = Fn;
+  }
+
   static void RegisterAsmTargetStreamer(Target &T,
                                         Target::AsmTargetStreamerCtorTy Fn) {
     T.AsmTargetStreamerCtorFn = Fn;
diff --git a/llvm/lib/MC/TargetRegistry.cpp b/llvm/lib/MC/TargetRegistry.cpp
index 3be6f1d4634990..0d343a2c4e4d5f 100644
--- a/llvm/lib/MC/TargetRegistry.cpp
+++ b/llvm/lib/MC/TargetRegistry.cpp
@@ -93,8 +93,14 @@ MCStreamer *Target::createAsmStreamer(MCContext &Ctx,
                                       std::unique_ptr<MCCodeEmitter> CE,
                                       std::unique_ptr<MCAsmBackend> TAB) const {
   formatted_raw_ostream &OSRef = *OS;
-  MCStreamer *S = llvm::createAsmStreamer(Ctx, std::move(OS), IP,
-                                          std::move(CE), std::move(TAB));
+  MCStreamer *S;
+  if (AsmStreamerCtorFn)
+    S = AsmStreamerCtorFn(Ctx, std::move(OS), IP, std::move(CE),
+                          std::move(TAB));
+  else
+    S = llvm::createAsmStreamer(Ctx, std::move(OS), IP, std::move(CE),
+                                std::move(TAB));
+
   createAsmTargetStreamer(*S, OSRef, IP);
   return S;
 }