MC Win64: Put unwind info for COMDAT code into the same COMDAT group

Summary:
This fixes a long standing issue where we would emit many little .text
sections and only one .pdata and .xdata section. Now we generate one
.pdata / .xdata pair per .text section and associate them correctly.

Fixes PR19667.

Reviewers: majnemer

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D5181

llvm-svn: 217176

4 files changed, 62 insertions, 27 deletions

diff --git a/llvm/lib/MC/MCAsmStreamer.cpp b/llvm/lib/MC/MCAsmStreamer.cpp
index fcf39b836fc..f60c7fc5041 100644
--- a/llvm/lib/MC/MCAsmStreamer.cpp
+++ b/llvm/lib/MC/MCAsmStreamer.cpp
@@ -1095,9 +1095,8 @@ void MCAsmStreamer::EmitWinEHHandlerData() {
   // We only do this so the section switch that terminates the handler
   // data block is visible.
   WinEH::FrameInfo *CurFrame = getCurrentWinFrameInfo();
-  StringRef Suffix = WinEH::UnwindEmitter::GetSectionSuffix(CurFrame->Function);
-  if (const MCSection *XData =
-          WinEH::UnwindEmitter::GetXDataSection(Suffix, getContext()))
+  if (const MCSection *XData = WinEH::UnwindEmitter::getXDataSection(
+          CurFrame->Function, getContext()))
     SwitchSectionNoChange(XData);
 
   OS << "\t.seh_handlerdata";
diff --git a/llvm/lib/MC/MCContext.cpp b/llvm/lib/MC/MCContext.cpp
index 7702da3540c..4266759b1f0 100644
--- a/llvm/lib/MC/MCContext.cpp
+++ b/llvm/lib/MC/MCContext.cpp
@@ -317,6 +317,22 @@ const MCSectionCOFF *MCContext::getCOFFSection(StringRef Section) {
   return Iter->second;
 }
 
+const MCSectionCOFF *
+MCContext::getAssociativeCOFFSection(const MCSectionCOFF *Sec,
+                                     const MCSymbol *KeySym) {
+  // Return the normal section if we don't have to be associative.
+  if (!KeySym)
+    return Sec;
+
+  // Make an associative section with the same name and kind as the normal
+  // section.
+  unsigned Characteristics =
+      Sec->getCharacteristics() | COFF::IMAGE_SCN_LNK_COMDAT;
+  return getCOFFSection(Sec->getSectionName(), Characteristics, Sec->getKind(),
+                        KeySym->getName(),
+                        COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE);
+}
+
 //===----------------------------------------------------------------------===//
 // Dwarf Management
 //===----------------------------------------------------------------------===//
diff --git a/llvm/lib/MC/MCWin64EH.cpp b/llvm/lib/MC/MCWin64EH.cpp
index 7394ba848bc..dfadb3cc42b 100644
--- a/llvm/lib/MC/MCWin64EH.cpp
+++ b/llvm/lib/MC/MCWin64EH.cpp
@@ -225,7 +225,7 @@ void UnwindEmitter::Emit(MCStreamer &Streamer) const {
   // Emit the unwind info structs first.
   for (const auto &CFI : Streamer.getWinFrameInfos()) {
     const MCSection *XData =
-        GetXDataSection(GetSectionSuffix(CFI->Function), Context);
+        getXDataSection(CFI->Function, Context);
     Streamer.SwitchSection(XData);
     EmitUnwindInfo(Streamer, CFI);
   }
@@ -233,7 +233,7 @@ void UnwindEmitter::Emit(MCStreamer &Streamer) const {
   // Now emit RUNTIME_FUNCTION entries.
   for (const auto &CFI : Streamer.getWinFrameInfos()) {
     const MCSection *PData =
-        GetPDataSection(GetSectionSuffix(CFI->Function), Context);
+        getPDataSection(CFI->Function, Context);
     Streamer.SwitchSection(PData);
     EmitRuntimeFunction(Streamer, CFI);
   }
@@ -245,7 +245,7 @@ void UnwindEmitter::EmitUnwindInfo(MCStreamer &Streamer,
   // here and from Emit().
   MCContext &context = Streamer.getContext();
   const MCSection *xdataSect =
-    GetXDataSection(GetSectionSuffix(info->Function), context);
+    getXDataSection(info->Function, context);
   Streamer.SwitchSection(xdataSect);
 
   llvm::EmitUnwindInfo(Streamer, info);
diff --git a/llvm/lib/MC/MCWinEH.cpp b/llvm/lib/MC/MCWinEH.cpp
index 8faf70737bf..f0c354feb61 100644
--- a/llvm/lib/MC/MCWinEH.cpp
+++ b/llvm/lib/MC/MCWinEH.cpp
@@ -17,27 +17,7 @@
 
 namespace llvm {
 namespace WinEH {
-const MCSection *UnwindEmitter::GetPDataSection(StringRef Suffix,
-                                                MCContext &Context) {
-  if (Suffix.empty())
-    return Context.getObjectFileInfo()->getPDataSection();
-  return Context.getCOFFSection((".pdata" + Suffix).str(),
-                                COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
-                                COFF::IMAGE_SCN_MEM_READ,
-                                SectionKind::getDataRel());
-}
-
-const MCSection *UnwindEmitter::GetXDataSection(StringRef Suffix,
-                                                MCContext &Context) {
-  if (Suffix.empty())
-    return Context.getObjectFileInfo()->getXDataSection();
-  return Context.getCOFFSection((".xdata" + Suffix).str(),
-                                COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
-                                COFF::IMAGE_SCN_MEM_READ,
-                                SectionKind::getDataRel());
-}
-
-StringRef UnwindEmitter::GetSectionSuffix(const MCSymbol *Function) {
+static StringRef getSectionSuffix(const MCSymbol *Function) {
   if (!Function || !Function->isInSection())
     return "";
 
@@ -59,6 +39,46 @@ StringRef UnwindEmitter::GetSectionSuffix(const MCSymbol *Function) {
 
   return "";
 }
+
+static const MCSection *getUnwindInfoSection(
+    StringRef SecName, const MCSectionCOFF *UnwindSec, const MCSymbol *Function,
+    MCContext &Context) {
+  // If Function is in a COMDAT, get or create an unwind info section in that
+  // COMDAT group.
+  if (Function && Function->isInSection()) {
+    const MCSectionCOFF *FunctionSection =
+        cast<MCSectionCOFF>(&Function->getSection());
+    if (FunctionSection->getCharacteristics() & COFF::IMAGE_SCN_LNK_COMDAT) {
+      return Context.getAssociativeCOFFSection(
+          UnwindSec, FunctionSection->getCOMDATSymbol());
+    }
+  }
+
+  // If Function is in a section other than .text, create a new .pdata section.
+  // Otherwise use the plain .pdata section.
+  StringRef Suffix = getSectionSuffix(Function);
+  if (Suffix.empty())
+    return UnwindSec;
+  return Context.getCOFFSection((SecName + Suffix).str(),
+                                COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
+                                COFF::IMAGE_SCN_MEM_READ,
+                                SectionKind::getDataRel());
+}
+
+const MCSection *UnwindEmitter::getPDataSection(const MCSymbol *Function,
+                                                MCContext &Context) {
+  const MCSectionCOFF *PData =
+      cast<MCSectionCOFF>(Context.getObjectFileInfo()->getPDataSection());
+  return getUnwindInfoSection(".pdata", PData, Function, Context);
+}
+
+const MCSection *UnwindEmitter::getXDataSection(const MCSymbol *Function,
+                                                MCContext &Context) {
+  const MCSectionCOFF *XData =
+      cast<MCSectionCOFF>(Context.getObjectFileInfo()->getXDataSection());
+  return getUnwindInfoSection(".xdata", XData, Function, Context);
+}
+
 }
 }