[MC] Suppress .Lcfi labels when emitting textual assembly

Summary:
This suppresses the generation of .Lcfi labels in our textual assembler.
It was annoying that this generated cascading .Lcfi labels:
  llc foo.ll -o - | llvm-mc | llvm-mc

After three trips through MCAsmStreamer, we'd have three labels in the
output when none are necessary. We should only bother creating the
labels and frame data when making a real object file.

This supercedes D38605, which moved the entire .seh_ implementation into
MCObjectStreamer.

This has the advantage that we do more checking when emitting textual
assembly, as a minor efficiency cost. Outputting textual assembly is not
performance critical, so this shouldn't matter.

Reviewers: majnemer, MatzeB

Subscribers: qcolombet, nemanjai, javed.absar, eraman, hiraditya, JDevlieghere, llvm-commits

Differential Revision: https://reviews.llvm.org/D38638

llvm-svn: 315259

2 files changed, 12 insertions, 4 deletions

diff --git a/llvm/lib/MC/MCObjectStreamer.cpp b/llvm/lib/MC/MCObjectStreamer.cpp
index 0beaf6b095a..65e5b839cae 100644
--- a/llvm/lib/MC/MCObjectStreamer.cpp
+++ b/llvm/lib/MC/MCObjectStreamer.cpp
@@ -146,6 +146,12 @@ void MCObjectStreamer::EmitValueImpl(const MCExpr *Value, unsigned Size,
   DF->getContents().resize(DF->getContents().size() + Size, 0);
 }
 
+MCSymbol *MCObjectStreamer::EmitCFILabel() {
+  MCSymbol *Label = getContext().createTempSymbol("cfi", true);
+  EmitLabel(Label);
+  return Label;
+}
+
 void MCObjectStreamer::EmitCFIStartProcImpl(MCDwarfFrameInfo &Frame) {
   // We need to create a local symbol to avoid relocations.
   Frame.Begin = getContext().createTempSymbol();
diff --git a/llvm/lib/MC/MCStreamer.cpp b/llvm/lib/MC/MCStreamer.cpp
index 7521a752fe5..866bad9515e 100644
--- a/llvm/lib/MC/MCStreamer.cpp
+++ b/llvm/lib/MC/MCStreamer.cpp
@@ -355,13 +355,13 @@ void MCStreamer::EmitCFIEndProc() {
 void MCStreamer::EmitCFIEndProcImpl(MCDwarfFrameInfo &Frame) {
   // Put a dummy non-null value in Frame.End to mark that this frame has been
   // closed.
-  Frame.End = (MCSymbol *) 1;
+  Frame.End = (MCSymbol *)1;
 }
 
 MCSymbol *MCStreamer::EmitCFILabel() {
-  MCSymbol *Label = getContext().createTempSymbol("cfi", true);
-  EmitLabel(Label);
-  return Label;
+  // Return a dummy non-null value so that label fields appear filled in when
+  // generating textual assembly.
+  return (MCSymbol *)1;
 }
 
 MCSymbol *MCStreamer::EmitCFICommon() {
@@ -735,6 +735,8 @@ void MCStreamer::EmitWindowsUnwindTables() {
 void MCStreamer::Finish() {
   if (!DwarfFrameInfos.empty() && !DwarfFrameInfos.back().End)
     report_fatal_error("Unfinished frame!");
+  if (!WinFrameInfos.empty() && !WinFrameInfos.back()->End)
+    report_fatal_error("Unfinished frame!");
 
   MCTargetStreamer *TS = getTargetStreamer();
   if (TS)