Merging r198744:

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r198744 | iain | 2014-01-08 05:22:54 -0500 (Wed, 08 Jan 2014) | 8 lines

[patch] Adjust behavior of FDE cross-section relocs for targets that don't support abs-differences.

Modern versions of OSX/Darwin's ld (ld64 > 97.17) have an optimisation present that allows the back end to omit relocations (and replace them with an absolute difference) for FDE some text section refs.

This patch allows a backend to opt-in to this behaviour by setting "DwarfFDESymbolsUseAbsDiff".  At present, this is only enabled for modern x86 OSX ports.

test changes by David Fang.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_34@205768 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 16 insertions, 6 deletions

diff --git a/lib/MC/MCAsmInfo.cpp b/lib/MC/MCAsmInfo.cpp
index 5882e696b7..d38f182fad 100644
--- a/lib/MC/MCAsmInfo.cpp
+++ b/lib/MC/MCAsmInfo.cpp
@@ -85,6 +85,7 @@ MCAsmInfo::MCAsmInfo() {
   SupportsDebugInformation = false;
   ExceptionsType = ExceptionHandling::None;
   DwarfUsesRelocationsAcrossSections = true;
+  DwarfFDESymbolsUseAbsDiff = false;
   DwarfRegNumForCFI = false;
   HasMicrosoftFastStdCallMangling = false;
   NeedsDwarfSectionOffsetDirective = false;
diff --git a/lib/MC/MCDwarf.cpp b/lib/MC/MCDwarf.cpp
index 1e5c2e34c4..9fd13ab3af 100644
--- a/lib/MC/MCDwarf.cpp
+++ b/lib/MC/MCDwarf.cpp
@@ -836,8 +836,9 @@ static unsigned getSizeForEncoding(MCStreamer &streamer,
   }
 }
 
-static void EmitSymbol(MCStreamer &streamer, const MCSymbol &symbol,
-                       unsigned symbolEncoding, const char *comment = 0) {
+static void EmitFDESymbol(MCStreamer &streamer, const MCSymbol &symbol,
+                       unsigned symbolEncoding, bool isEH,
+                       const char *comment = 0) {
   MCContext &context = streamer.getContext();
   const MCAsmInfo *asmInfo = context.getAsmInfo();
   const MCExpr *v = asmInfo->getExprForFDESymbol(&symbol,
@@ -845,7 +846,10 @@ static void EmitSymbol(MCStreamer &streamer, const MCSymbol &symbol,
                                                  streamer);
   unsigned size = getSizeForEncoding(streamer, symbolEncoding);
   if (streamer.isVerboseAsm() && comment) streamer.AddComment(comment);
-  streamer.EmitAbsValue(v, size);
+  if (asmInfo->doDwarfFDESymbolsUseAbsDiff() && isEH)
+    streamer.EmitAbsValue(v, size);
+  else
+    streamer.EmitValue(v, size);
 }
 
 static void EmitPersonality(MCStreamer &streamer, const MCSymbol &symbol,
@@ -1344,7 +1348,7 @@ MCSymbol *FrameEmitterImpl::EmitFDE(MCStreamer &streamer,
   unsigned PCEncoding = IsEH ? MOFI->getFDEEncoding(UsingCFI)
                              : (unsigned)dwarf::DW_EH_PE_absptr;
   unsigned PCSize = getSizeForEncoding(streamer, PCEncoding);
-  EmitSymbol(streamer, *frame.Begin, PCEncoding, "FDE initial location");
+  EmitFDESymbol(streamer, *frame.Begin, PCEncoding, IsEH, "FDE initial location");
 
   // PC Range
   const MCExpr *Range = MakeStartMinusEndExpr(streamer, *frame.Begin,
@@ -1364,8 +1368,8 @@ MCSymbol *FrameEmitterImpl::EmitFDE(MCStreamer &streamer,
 
     // Augmentation Data
     if (frame.Lsda)
-      EmitSymbol(streamer, *frame.Lsda, frame.LsdaEncoding,
-                 "Language Specific Data Area");
+      EmitFDESymbol(streamer, *frame.Lsda, frame.LsdaEncoding, true,
+                    "Language Specific Data Area");
   }
 
   // Call Frame Instructions
diff --git a/lib/Target/X86/MCTargetDesc/X86MCAsmInfo.cpp b/lib/Target/X86/MCTargetDesc/X86MCAsmInfo.cpp
index 3861e1ce29..6a173fd309 100644
--- a/lib/Target/X86/MCTargetDesc/X86MCAsmInfo.cpp
+++ b/lib/Target/X86/MCTargetDesc/X86MCAsmInfo.cpp
@@ -65,6 +65,11 @@ X86MCAsmInfoDarwin::X86MCAsmInfoDarwin(const Triple &T) {
 
   // Exceptions handling
   ExceptionsType = ExceptionHandling::DwarfCFI;
+
+  // FIXME: this should not depend on the target OS version, but on the ld64
+  // version in use.  From at least >= ld64-97.17 (Xcode 3.2.6) the abs-ified
+  // FDE relocs may be used.
+  DwarfFDESymbolsUseAbsDiff = T.isMacOSX() && !T.isMacOSXVersionLT(10, 6);
 }
 
 X86_64MCAsmInfoDarwin::X86_64MCAsmInfoDarwin(const Triple &Triple)