MCAsmStreamer: Omit initial ".text"

llvm-mc --assemble prints an initial `.text` from `initSections`.
This is weird for quick assembly tasks that do not specify `.text`.

Omit the .text by moving section directive printing from `changeSection`
to `switchSection`. switchSectionNoPrint now correctly calls the
`changeSection` hook (needed by MachO).

The initial directives of clang -S are now reordered. On ELF targets, we
get `.file "a.c"; .text` instead of `.text; .file "a.c"`.
If there is no function, `.text` will be omitted.

1 files changed, 5 insertions, 2 deletions

diff --git a/llvm/lib/MC/MCStreamer.cpp b/llvm/lib/MC/MCStreamer.cpp
index 5703cfd0..ccf65df 100644
--- a/llvm/lib/MC/MCStreamer.cpp
+++ b/llvm/lib/MC/MCStreamer.cpp
@@ -414,7 +414,7 @@ void MCStreamer::emitEHSymAttributes(const MCSymbol *Symbol,
 }
 
 void MCStreamer::initSections(bool NoExecStack, const MCSubtargetInfo &STI) {
-  switchSection(getContext().getObjectFileInfo()->getTextSection());
+  switchSectionNoPrint(getContext().getObjectFileInfo()->getTextSection());
 }
 
 void MCStreamer::emitLabel(MCSymbol *Symbol, SMLoc Loc) {
@@ -1332,7 +1332,10 @@ bool MCStreamer::switchSection(MCSection *Section, const MCExpr *SubsecExpr) {
 void MCStreamer::switchSectionNoPrint(MCSection *Section) {
   SectionStack.back().second = SectionStack.back().first;
   SectionStack.back().first = MCSectionSubPair(Section, 0);
-  CurFrag = &Section->getDummyFragment();
+  changeSection(Section, 0);
+  MCSymbol *Sym = Section->getBeginSymbol();
+  if (Sym && !Sym->isInSection())
+    emitLabel(Sym);
 }
 
 MCSymbol *MCStreamer::endSection(MCSection *Section) {