CodeGen: avoid emitting unnecessary CFI

[compnerd]

Summary

Remove unnecessary clutter in assembly output. When using SjLj EH, the CFI is
not actually used for anything. Do not emit the CFI needlessly. The minor test
adjustments are interesting. The prologue test was just overzealous matcching.
The interesting case is the LSDA change. It was originally added to ensure that
various compilations did not mangle the name (it explicitly checked the name!).
However, subsequent cleanups made it more reliant on the CFI to find the name.
Parse the generated code flow to generically find the label still.

[t.p.northover]

I think this is reasonable. As far as I can tell the __eh_frame sections really are unused.

[compnerd]

SVN r275614

lib/CodeGen/AsmPrinter/DwarfCFIException.cpp

 /// endModule - Emit all exception information that should come after the
 /// content.
 void DwarfCFIException::endModule() {
-  if (moveTypeModule == AsmPrinter::CFI_M_Debug)
-    Asm->OutStreamer->EmitCFISections(false, true);
-
   // SjLj uses this pass and it doesn't need this info.
   if (!Asm->MAI->usesCFIForEH())
     return;
 
+  if (moveTypeModule == AsmPrinter::CFI_M_Debug)
+    Asm->OutStreamer->EmitCFISections(false, true);
+
   const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
 
   unsigned PerEncoding = TLOF.getPersonalityEncoding();

   shouldEmitLSDA = shouldEmitPersonality &&
     LSDAEncoding != dwarf::DW_EH_PE_omit;
 
-  shouldEmitCFI = shouldEmitPersonality || shouldEmitMoves;
+  shouldEmitCFI = MF->getMMI().getContext().getAsmInfo()->usesCFIForEH() &&
+                  (shouldEmitPersonality || shouldEmitMoves);
   beginFragment(&*MF->begin(), getExceptionSym);
 }
 

test/CodeGen/ARM/2009-08-31-LSDA-Name.ll

 ; RUN: llc < %s -mtriple=arm-apple-darwin9 -march=arm | FileCheck %s
 
-; CHECK: .cfi_lsda 16, [[LABEL:.*]]
-; CHECK: .long  [[LABEL]]-
-; CHECK: [[LABEL]]:
+; CHECK: ldr r0, [[CPI_PERSONALITY:[A-Za-z0-9_]+]]
+; CHECK: ldr r0, [[CPI_LSDA:[A-Za-z0-9_]+]]
+; CHECK: [[CPI_LSDA]]:
+; CHECK: .long  [[LSDA_LABEL:[A-Za-z0-9_]+]]-
+; CHECK: [[LSDA_LABEL]]:
 ; CHECK: .byte   255                     @ @LPStart Encoding = omit
 
 %struct.A = type { i32* }

test/DebugInfo/ARM/prologue_end.ll

 
 define void @prologue_end_test() nounwind uwtable !dbg !4 {
   ; CHECK: prologue_end_test:
-  ; CHECK: .cfi_startproc
   ; CHECK: push {r7, lr}
   ; CHECK: {{mov r7, sp|add r7, sp}}
   ; CHECK: sub sp