[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. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198744 91177308-0d34-0410-b5e6-96231b3b80d8
Bigcheese · Jan 8, 2014 · 9c0a05c · 9c0a05c
1 parent 4712264
commit 9c0a05c
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Showing 5 changed files with 70 additions and 7 deletions.
diff --git a/include/llvm/MC/MCAsmInfo.h b/include/llvm/MC/MCAsmInfo.h
@@ -292,6 +292,10 @@ namespace llvm {
     /// uses relocations for references to other .debug_* sections.
     bool DwarfUsesRelocationsAcrossSections;
 
+    /// DwarfFDESymbolsUseAbsDiff - true if DWARF FDE symbol reference
+    /// relocations should be replaced by an absolute difference.
+    bool DwarfFDESymbolsUseAbsDiff;
+
     /// DwarfRegNumForCFI - True if dwarf register numbers are printed
     /// instead of symbolic register names in .cfi_* directives.
     bool DwarfRegNumForCFI;  // Defaults to false;
@@ -513,6 +517,9 @@ namespace llvm {
     bool doesDwarfUseRelocationsAcrossSections() const {
       return DwarfUsesRelocationsAcrossSections;
     }
+    bool doDwarfFDESymbolsUseAbsDiff() const {
+      return DwarfFDESymbolsUseAbsDiff;
+    }
     bool useDwarfRegNumForCFI() const {
       return DwarfRegNumForCFI;
     }

diff --git a/lib/MC/MCAsmInfo.cpp b/lib/MC/MCAsmInfo.cpp
@@ -84,6 +84,7 @@ MCAsmInfo::MCAsmInfo() {
   SupportsDebugInformation = false;
   ExceptionsType = ExceptionHandling::None;
   DwarfUsesRelocationsAcrossSections = true;
+  DwarfFDESymbolsUseAbsDiff = false;
   DwarfRegNumForCFI = false;
   NeedsDwarfSectionOffsetDirective = false;
   UseParensForSymbolVariant = false;

diff --git a/lib/MC/MCDwarf.cpp b/lib/MC/MCDwarf.cpp
@@ -839,16 +839,20 @@ 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,
                                                  symbolEncoding,
                                                  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,
@@ -1347,7 +1351,7 @@ 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,
@@ -1367,8 +1371,8 @@ 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
@@ -71,6 +71,11 @@ X86MCAsmInfoDarwin::X86MCAsmInfoDarwin(const Triple &T) {
   // rather than OS version
   if (T.isMacOSX() && T.isMacOSXVersionLT(10, 6))
     HasWeakDefCanBeHiddenDirective = false;
+
+  // 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)

diff --git a/test/CodeGen/X86/pr10420.ll b/test/CodeGen/X86/pr10420.ll
@@ -1,4 +1,9 @@
-; RUN: llc < %s -mtriple=x86_64-apple-macosx -disable-cfi | FileCheck %s
+; RUN: llc < %s -mtriple=x86_64-apple-macosx10.7 -disable-cfi | FileCheck --check-prefix=CHECK-64-D11 %s
+; RUN: llc < %s -mtriple=x86_64-apple-macosx10.6 -disable-cfi | FileCheck %s
+; RUN: llc < %s -mtriple=x86_64-apple-macosx10.5 -disable-cfi | FileCheck --check-prefix=CHECK-64-D89 %s
+; RUN: llc < %s -mtriple=i686-apple-macosx10.6 -disable-cfi | FileCheck --check-prefix=CHECK-I686-D10 %s
+; RUN: llc < %s -mtriple=i686-apple-macosx10.5 -disable-cfi | FileCheck --check-prefix=CHECK-I686-D89 %s
+; RUN: llc < %s -mtriple=i686-apple-macosx10.4 -disable-cfi | FileCheck --check-prefix=CHECK-I686-D89 %s
 
 define private void @foo() {
        ret void
@@ -19,3 +24,44 @@ define void @bar() {
 ; CHECK: Ltmp19:
 ; CHECK-NEXT: Ltmp20 = Ltmp2-Ltmp19                   ## FDE initial location
 ; CHECK-NEXT:         .quad   Ltmp20
+
+
+; CHECK-64-D11: Ltmp13:
+; CHECK-64-D11-NEXT: Ltmp14 = L_foo-Ltmp13                   ## FDE initial location
+; CHECK-64-D11-NEXT:         .quad   Ltmp14
+
+; CHECK-64-D11: Ltmp20:
+; CHECK-64-D11-NEXT: Ltmp21 = Ltmp2-Ltmp20                   ## FDE initial location
+; CHECK-64-D11-NEXT:         .quad   Ltmp21
+
+
+; CHECK-64-D89: Ltmp12:
+; CHECK-64-D89-NEXT: .quad	L_foo-Ltmp12                   ## FDE initial location
+; CHECK-64-D89-NEXT: Ltmp13 = (Ltmp0-L_foo)-0                   ## FDE address range
+; CHECK-64-D89-NEXT:         .quad   Ltmp13
+
+; CHECK-64-D89: Ltmp18:
+; CHECK-64-D89-NEXT: .quad	Ltmp2-Ltmp18                   ## FDE initial location
+; CHECK-64-D89-NEXT: Ltmp19 = (Ltmp4-Ltmp2)-0                   ## FDE address range
+; CHECK-64-D89-NEXT:         .quad   Ltmp19
+
+
+; CHECK-I686-D10: Ltmp12:
+; CHECK-I686-D10-NEXT: Ltmp13 = L_foo-Ltmp12                   ## FDE initial location
+; CHECK-I686-D10-NEXT:         .long   Ltmp13
+
+; CHECK-I686-D10: Ltmp19:
+; CHECK-I686-D10-NEXT: Ltmp20 = Ltmp2-Ltmp19                   ## FDE initial location
+; CHECK-I686-D10-NEXT:         .long   Ltmp20
+
+
+; CHECK-I686-D89: Ltmp12:
+; CHECK-I686-D89-NEXT: .long	L_foo-Ltmp12                   ## FDE initial location
+; CHECK-I686-D89-NEXT: Ltmp13 = (Ltmp0-L_foo)-0                   ## FDE address range
+; CHECK-I686-D89-NEXT:         .long   Ltmp13
+
+; CHECK-I686-D89: Ltmp18:
+; CHECK-I686-D89-NEXT: .long	Ltmp2-Ltmp18                   ## FDE initial location
+; CHECK-I686-D89-NEXT: Ltmp19 = (Ltmp4-Ltmp2)-0                   ## FDE address range
+; CHECK-I686-D89-NEXT:         .long   Ltmp19
+