MC: Simplify fragment reuse determination

First, avoid checking MCSubtargetInfo by reducing unnecessary overhead
introduced in https://reviews.llvm.org/D44928 . That change passed STI
to both FT_Data and FT_Relaxable fragments, but STI is only necessary
for FT_Relaxable.

The use of STI in FT_Data was added for:

* Bundle alignment mode, which has been removed (#148781).
* ARM, which inappropriately uses STI in `ARMAsmBackend::applyFixup` due
  to tech debt, unlike other targets. All tests passed even without the
  `copySTI` change.

To ensure safety, `copySTI` now starts a new fragment to prevent mixed
STI values.

Second, avoid checking LinkerRelaxable by eagerly starting a new
fragment when a FT_Data/FT_Align fragment is marked linker-relaxable.
There is currently an extra empty FT_Data if an alignment immediately
follows a linker-relaxable fragment, which will be improved in the
future when FT_Align information is moved to the variable-tail.

Pull Request: https://github.com/llvm/llvm-project/pull/149471

1 files changed, 13 insertions, 0 deletions

diff --git a/llvm/lib/MC/MCStreamer.cpp b/llvm/lib/MC/MCStreamer.cpp
index d814ab88..c3ecf8f 100644
--- a/llvm/lib/MC/MCStreamer.cpp
+++ b/llvm/lib/MC/MCStreamer.cpp
@@ -1404,6 +1404,19 @@ MCSymbol *MCStreamer::endSection(MCSection *Section) {
   return Sym;
 }
 
+void MCStreamer::insert(MCFragment *F) {
+  auto *Sec = CurFrag->getParent();
+  F->setParent(Sec);
+  F->setLayoutOrder(CurFrag->getLayoutOrder() + 1);
+  CurFrag->Next = F;
+  CurFrag = F;
+  Sec->curFragList()->Tail = F;
+}
+
+void MCStreamer::newFragment() {
+  insert(getContext().allocFragment<MCFragment>());
+}
+
 static VersionTuple
 targetVersionOrMinimumSupportedOSVersion(const Triple &Target,
                                          VersionTuple TargetVersion) {