From e3cd13f0e2d4e2ef30f8a57c0a82d328102eeb26 Mon Sep 17 00:00:00 2001
From: Bill Wendling <isanbard@gmail.com>
Date: Thu, 23 Jun 2011 01:06:23 +0000
Subject: [PATCH] Some skeleton code to emit the compact unwind. If the
 information is unable to be emitted in a compact way, we then default to
 emitting a CIE and FDE.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@133676 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/MC/MCDwarf.cpp | 64 +++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 63 insertions(+), 1 deletion(-)

diff --git a/lib/MC/MCDwarf.cpp b/lib/MC/MCDwarf.cpp
index 97e7dbdf868..937dad41026 100644
--- a/lib/MC/MCDwarf.cpp
+++ b/lib/MC/MCDwarf.cpp
@@ -507,6 +507,12 @@ namespace {
       SectionStart(sectionStart) {
     }
 
+    /// EmitCompactUnwind - Emit the unwind information in a compact way. If
+    /// we're successful, return 'true'. Otherwise, return 'false' and it will
+    /// emit the normal CIE and FDE.
+    bool EmitCompactUnwind(MCStreamer &streamer,
+                           const MCDwarfFrameInfo &frame);
+
     const MCSymbol &EmitCIE(MCStreamer &streamer,
                             const MCSymbol *personality,
                             unsigned personalityEncoding,
@@ -620,6 +626,55 @@ void FrameEmitterImpl::EmitCFIInstructions(MCStreamer &streamer,
   }
 }
 
+/// EmitCompactUnwind - Emit the unwind information in a compact way. If we're
+/// successful, return 'true'. Otherwise, return 'false' and it will emit the
+/// normal CIE and FDE.
+bool FrameEmitterImpl::EmitCompactUnwind(MCStreamer &Streamer,
+                                         const MCDwarfFrameInfo &Frame) {
+#if 1
+  return false;
+#else
+  MCContext &Context = Streamer.getContext();
+  const TargetAsmInfo &TAI = Context.getTargetAsmInfo();
+  Streamer.SwitchSection(TAI.getCompactUnwindSection());
+
+  unsigned FDEEncoding = TAI.getFDEEncoding(UsingCFI);
+  unsigned Size = getSizeForEncoding(Streamer, FDEEncoding);
+
+  // range-start range-length  compact-unwind-enc personality-func   lsda
+  //  _foo       LfooEnd-_foo  0x00000023          0                 0
+  //  _bar       LbarEnd-_bar  0x00000025         __gxx_personality  except_tab1
+  //
+  //   .section __LD,__compact_unwind,regular,debug
+  //
+  //   # compact unwind for _foo
+  //   .quad _foo
+  //   .set L1,LfooEnd-_foo
+  //   .long L1
+  //   .long 0x01010001
+  //   .quad 0
+  //   .quad 0
+  //
+  //   # compact unwind for _bar
+  //   .quad _bar
+  //   .set L2,LbarEnd-_bar
+  //   .long L2
+  //   .long 0x01020011
+  //   .quad __gxx_personality
+  //   .quad except_tab1
+
+  // Range Start
+  EmitSymbol(Streamer, *Frame.Begin, FDEEncoding);
+
+  // Range Length
+  const MCExpr *Range = MakeStartMinusEndExpr(Streamer, *Frame.Begin,
+                                              *Frame.End, 0);
+  Streamer.EmitAbsValue(Range, Size);
+
+  return true;
+#endif
+}
+
 const MCSymbol &FrameEmitterImpl::EmitCIE(MCStreamer &streamer,
                                           const MCSymbol *personality,
                                           unsigned personalityEncoding,
@@ -846,7 +901,8 @@ void MCDwarfFrameEmitter::Emit(MCStreamer &streamer,
   MCContext &context = streamer.getContext();
   const TargetAsmInfo &asmInfo = context.getTargetAsmInfo();
   const MCSection &section = isEH ?
-    *asmInfo.getEHFrameSection() : *asmInfo.getDwarfFrameSection();
+    *asmInfo.getEHFrameSection() :
+    *asmInfo.getDwarfFrameSection();
   streamer.SwitchSection(&section);
   MCSymbol *SectionStart = context.CreateTempSymbol();
   streamer.EmitLabel(SectionStart);
@@ -861,11 +917,17 @@ void MCDwarfFrameEmitter::Emit(MCStreamer &streamer,
     CIEKey key(frame.Personality, frame.PersonalityEncoding,
                frame.LsdaEncoding);
     const MCSymbol *&cieStart = isEH ? CIEStarts[key] : DummyDebugKey;
+    if (isEH && asmInfo.getSupportsCompactUnwindInfo() &&
+        Emitter.EmitCompactUnwind(streamer, frame))
+      continue;
+
     if (!cieStart)
       cieStart = &Emitter.EmitCIE(streamer, frame.Personality,
                                   frame.PersonalityEncoding, frame.Lsda,
                                   frame.LsdaEncoding);
+
     fdeEnd = Emitter.EmitFDE(streamer, *cieStart, frame);
+
     if (i != n - 1)
       streamer.EmitLabel(fdeEnd);
   }