From: Bill Wendling <isanbard@gmail.com>
Date: Fri, 18 Sep 2009 21:14:36 +0000 (+0000)
Subject: It's inefficient to have place the exception tables (which contain the LSDA)
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=296ab7e5445f0402d0aae3814c38f964d6f547fb;p=oota-llvm.git

It's inefficient to have place the exception tables (which contain the LSDA)
into the __DATA section. At launch time, dyld has to update most of the section
to fix up the type info pointers. It's better to place it into the __TEXT
section and use pc-rel indirect pointer encodings. Similar to the personality
routine.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@82274 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/CodeGen/AsmPrinter/DwarfException.cpp b/lib/CodeGen/AsmPrinter/DwarfException.cpp
index 626523b820f..f3897ff489f 100644
--- a/lib/CodeGen/AsmPrinter/DwarfException.cpp
+++ b/lib/CodeGen/AsmPrinter/DwarfException.cpp
@@ -893,14 +893,49 @@ void DwarfException::EmitExceptionTable() {
   // of the catch clauses as they appear in the source code, and must be kept in
   // the same order. As a result, changing the order of the catch clause would
   // change the semantics of the program.
+  const TargetLoweringObjectFile &TLOF = Asm->getObjFileLowering();
+  unsigned Index = 1;
+
   for (std::vector<GlobalVariable *>::const_reverse_iterator
-         I = TypeInfos.rbegin(), E = TypeInfos.rend(); I != E; ++I) {
-    const GlobalVariable *GV = *I;
-    PrintRelDirective();
+         I = TypeInfos.rbegin(), E = TypeInfos.rend(); I != E; ++I, ++Index) {
+    const GlobalVariable *TI = *I;
+
+    if (TI) {
+      if (TTypeFormat == dwarf::DW_EH_PE_absptr) {
+        // Print out the unadorned name of the type info.
+        PrintRelDirective();
+        O << Asm->Mang->getMangledName(TI);
+      } else {
+        bool IsTypeInfoIndirect = false, IsTypeInfoPCRel = false;
+        const MCExpr *TypeInfoRef =
+          TLOF.getSymbolForDwarfGlobalReference(TI, Asm->Mang, Asm->MMI,
+                                                IsTypeInfoIndirect,
+                                                IsTypeInfoPCRel);
+
+        if (!IsTypeInfoPCRel) {
+          // If the reference to the type info symbol is not already
+          // pc-relative, then we need to subtract our current address from it.
+          // Do this by emitting a label and subtracting it from the expression
+          // we already have.  This is equivalent to emitting "foo - .", but we
+          // have to emit the label for "." directly.
+          SmallString<64> Name;
+          raw_svector_ostream(Name) << MAI->getPrivateGlobalPrefix()
+            << "typeinforef_addr" << Asm->getFunctionNumber() << "_" << Index;
+          MCSymbol *DotSym = Asm->OutContext.GetOrCreateSymbol(Name.str());
+          Asm->OutStreamer.EmitLabel(DotSym);
+
+          TypeInfoRef =
+            MCBinaryExpr::CreateSub(TypeInfoRef,
+                                    MCSymbolRefExpr::Create(DotSym,
+                                                            Asm->OutContext),
+                                    Asm->OutContext);
+        }
 
-    if (GV) {
-      O << Asm->Mang->getMangledName(GV);
+        O << MAI->getData32bitsDirective();
+        TypeInfoRef->print(O, MAI);
+      }
     } else {
+      PrintRelDirective();
       O << "0x0";
     }
 
diff --git a/lib/Target/TargetLoweringObjectFile.cpp b/lib/Target/TargetLoweringObjectFile.cpp
index c1aab9921fb..b49164aa177 100644
--- a/lib/Target/TargetLoweringObjectFile.cpp
+++ b/lib/Target/TargetLoweringObjectFile.cpp
@@ -782,8 +782,8 @@ void TargetLoweringObjectFileMachO::Initialize(MCContext &Ctx,
   }
 
   // Exception Handling.
-  LSDASection = getMachOSection("__DATA", "__gcc_except_tab", 0,
-                                SectionKind::getDataRel());
+  LSDASection = getMachOSection("__TEXT", "__gcc_except_tab", 0,
+                                SectionKind::getReadOnly());
   EHFrameSection =
     getMachOSection("__TEXT", "__eh_frame",
                     MCSectionMachO::S_COALESCED |