CodeGen: Stick constant pool entries in COMDAT sections for WinCOFF

COFF lacks a feature that other object file formats support: mergeable
sections.

To work around this, MSVC sticks constant pool entries in special COMDAT
sections so that each constant is in it's own section.  This permits
unused constants to be dropped and it also allows duplicate constants in
different translation units to get merged together.

This fixes PR20262.

Differential Revision: http://reviews.llvm.org/D4482

llvm-svn: 213006

11 files changed, 127 insertions, 16 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index 4c3e6aa4732..424e759caa8 100644
--- a/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -1064,7 +1064,11 @@ void AsmPrinter::EmitConstantPool() {
 
     SectionKind Kind = CPE.getSectionKind(TM.getDataLayout());
 
-    const MCSection *S = getObjFileLowering().getSectionForConstant(Kind);
+    const Constant *C = nullptr;
+    if (!CPE.isMachineConstantPoolEntry())
+      C = CPE.Val.ConstVal;
+
+    const MCSection *S = getObjFileLowering().getSectionForConstant(Kind, C);
 
     // The number of sections are small, just do a linear search from the
     // last section to the first.
@@ -1087,13 +1091,22 @@ void AsmPrinter::EmitConstantPool() {
   }
 
   // Now print stuff into the calculated sections.
+  const MCSection *CurSection = nullptr;
+  unsigned Offset = 0;
   for (unsigned i = 0, e = CPSections.size(); i != e; ++i) {
-    OutStreamer.SwitchSection(CPSections[i].S);
-    EmitAlignment(Log2_32(CPSections[i].Alignment));
-
-    unsigned Offset = 0;
     for (unsigned j = 0, ee = CPSections[i].CPEs.size(); j != ee; ++j) {
       unsigned CPI = CPSections[i].CPEs[j];
+      MCSymbol *Sym = GetCPISymbol(CPI);
+      if (!Sym->isUndefined())
+        continue;
+
+      if (CurSection != CPSections[i].S) {
+        OutStreamer.SwitchSection(CPSections[i].S);
+        EmitAlignment(Log2_32(CPSections[i].Alignment));
+        CurSection = CPSections[i].S;
+        Offset = 0;
+      }
+
       MachineConstantPoolEntry CPE = CP[CPI];
 
       // Emit inter-object padding for alignment.
@@ -1103,8 +1116,8 @@ void AsmPrinter::EmitConstantPool() {
 
       Type *Ty = CPE.getType();
       Offset = NewOffset + TM.getDataLayout()->getTypeAllocSize(Ty);
-      OutStreamer.EmitLabel(GetCPISymbol(CPI));
 
+      OutStreamer.EmitLabel(Sym);
       if (CPE.isMachineConstantPoolEntry())
         EmitMachineConstantPoolValue(CPE.Val.MachineCPVal);
       else
@@ -1142,7 +1155,8 @@ void AsmPrinter::EmitJumpTableInfo() {
   } else {
     // Otherwise, drop it in the readonly section.
     const MCSection *ReadOnlySection =
-      getObjFileLowering().getSectionForConstant(SectionKind::getReadOnly());
+        getObjFileLowering().getSectionForConstant(SectionKind::getReadOnly(),
+                                                   /*C=*/nullptr);
     OutStreamer.SwitchSection(ReadOnlySection);
     JTInDiffSection = true;
   }
diff --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index 03f4a51e8b6..f59efa35031 100644
--- a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -338,8 +338,9 @@ SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
 /// getSectionForConstant - Given a mergeable constant with the
 /// specified size and relocation information, return a section that it
 /// should be placed in.
-const MCSection *TargetLoweringObjectFileELF::
-getSectionForConstant(SectionKind Kind) const {
+const MCSection *
+TargetLoweringObjectFileELF::getSectionForConstant(SectionKind Kind,
+                                                   const Constant *C) const {
   if (Kind.isMergeableConst4() && MergeableConst4Section)
     return MergeableConst4Section;
   if (Kind.isMergeableConst8() && MergeableConst8Section)
@@ -654,7 +655,8 @@ SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
 }
 
 const MCSection *
-TargetLoweringObjectFileMachO::getSectionForConstant(SectionKind Kind) const {
+TargetLoweringObjectFileMachO::getSectionForConstant(SectionKind Kind,
+                                                     const Constant *C) const {
   // If this constant requires a relocation, we have to put it in the data
   // segment, not in the text segment.
   if (Kind.isDataRel() || Kind.isReadOnlyWithRel())
diff --git a/llvm/lib/MC/MCContext.cpp b/llvm/lib/MC/MCContext.cpp
index 960a0716e93..7702da3540c 100644
--- a/llvm/lib/MC/MCContext.cpp
+++ b/llvm/lib/MC/MCContext.cpp
@@ -291,7 +291,7 @@ const MCSectionCOFF *MCContext::getCOFFSection(StringRef Section,
   if (!IterBool.second)
     return Iter->second;
 
-  const MCSymbol *COMDATSymbol = nullptr;
+  MCSymbol *COMDATSymbol = nullptr;
   if (!COMDATSymName.empty())
     COMDATSymbol = GetOrCreateSymbol(COMDATSymName);
 
diff --git a/llvm/lib/Target/NVPTX/NVPTXTargetObjectFile.h b/llvm/lib/Target/NVPTX/NVPTXTargetObjectFile.h
index 0b438c521a2..ba8086d7888 100644
--- a/llvm/lib/Target/NVPTX/NVPTXTargetObjectFile.h
+++ b/llvm/lib/Target/NVPTX/NVPTXTargetObjectFile.h
@@ -87,7 +87,8 @@ public:
         new NVPTXSection(MCSection::SV_ELF, SectionKind::getMetadata());
   }
 
-  const MCSection *getSectionForConstant(SectionKind Kind) const override {
+  const MCSection *getSectionForConstant(SectionKind Kind,
+                                         const Constant *C) const override {
     return ReadOnlySection;
   }
 
diff --git a/llvm/lib/Target/TargetLoweringObjectFile.cpp b/llvm/lib/Target/TargetLoweringObjectFile.cpp
index 39e045919ab..2569e922641 100644
--- a/llvm/lib/Target/TargetLoweringObjectFile.cpp
+++ b/llvm/lib/Target/TargetLoweringObjectFile.cpp
@@ -297,7 +297,8 @@ TargetLoweringObjectFile::SelectSectionForGlobal(const GlobalValue *GV,
 /// specified size and relocation information, return a section that it
 /// should be placed in.
 const MCSection *
-TargetLoweringObjectFile::getSectionForConstant(SectionKind Kind) const {
+TargetLoweringObjectFile::getSectionForConstant(SectionKind Kind,
+                                                const Constant *C) const {
   if (Kind.isReadOnly() && ReadOnlySection != nullptr)
     return ReadOnlySection;
 
diff --git a/llvm/lib/Target/X86/X86AsmPrinter.cpp b/llvm/lib/Target/X86/X86AsmPrinter.cpp
index 1dca5689ade..57c7a62bd5c 100644
--- a/llvm/lib/Target/X86/X86AsmPrinter.cpp
+++ b/llvm/lib/Target/X86/X86AsmPrinter.cpp
@@ -18,6 +18,7 @@
 #include "X86InstrInfo.h"
 #include "X86MachineFunctionInfo.h"
 #include "llvm/ADT/SmallString.h"
+#include "llvm/CodeGen/MachineConstantPool.h"
 #include "llvm/CodeGen/MachineModuleInfoImpls.h"
 #include "llvm/CodeGen/MachineValueType.h"
 #include "llvm/CodeGen/TargetLoweringObjectFileImpl.h"
@@ -29,6 +30,7 @@
 #include "llvm/MC/MCAsmInfo.h"
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCExpr.h"
+#include "llvm/MC/MCSectionCOFF.h"
 #include "llvm/MC/MCSectionMachO.h"
 #include "llvm/MC/MCStreamer.h"
 #include "llvm/MC/MCSymbol.h"
@@ -549,6 +551,26 @@ emitNonLazySymbolPointer(MCStreamer &OutStreamer, MCSymbol *StubLabel,
         4 /*size*/);
 }
 
+MCSymbol *X86AsmPrinter::GetCPISymbol(unsigned CPID) const {
+  if (Subtarget->isTargetKnownWindowsMSVC()) {
+    const MachineConstantPoolEntry &CPE =
+        MF->getConstantPool()->getConstants()[CPID];
+    if (!CPE.isMachineConstantPoolEntry()) {
+      SectionKind Kind = CPE.getSectionKind(TM.getDataLayout());
+      const Constant *C = CPE.Val.ConstVal;
+      const MCSectionCOFF *S = cast<MCSectionCOFF>(
+          getObjFileLowering().getSectionForConstant(Kind, C));
+      if (MCSymbol *Sym = S->getCOMDATSymbol()) {
+        if (Sym->isUndefined())
+          OutStreamer.EmitSymbolAttribute(Sym, MCSA_Global);
+        return Sym;
+      }
+    }
+  }
+
+  return AsmPrinter::GetCPISymbol(CPID);
+}
+
 void X86AsmPrinter::GenerateExportDirective(const MCSymbol *Sym, bool IsData) {
   SmallString<128> Directive;
   raw_svector_ostream OS(Directive);
diff --git a/llvm/lib/Target/X86/X86AsmPrinter.h b/llvm/lib/Target/X86/X86AsmPrinter.h
index e4eef5dbd79..b1bbe8e41cc 100644
--- a/llvm/lib/Target/X86/X86AsmPrinter.h
+++ b/llvm/lib/Target/X86/X86AsmPrinter.h
@@ -50,6 +50,9 @@ class LLVM_LIBRARY_VISIBILITY X86AsmPrinter : public AsmPrinter {
                              unsigned AsmVariant, const char *ExtraCode,
                              raw_ostream &OS) override;
 
+  /// \brief Return the symbol for the specified constant pool entry.
+  MCSymbol *GetCPISymbol(unsigned CPID) const override;
+
   bool runOnMachineFunction(MachineFunction &F) override;
 };
 
diff --git a/llvm/lib/Target/X86/X86TargetObjectFile.cpp b/llvm/lib/Target/X86/X86TargetObjectFile.cpp
index 8157085feae..c7802320b06 100644
--- a/llvm/lib/Target/X86/X86TargetObjectFile.cpp
+++ b/llvm/lib/Target/X86/X86TargetObjectFile.cpp
@@ -8,10 +8,12 @@
 //===----------------------------------------------------------------------===//
 
 #include "X86TargetObjectFile.h"
+#include "llvm/ADT/StringExtras.h"
 #include "llvm/IR/Mangler.h"
 #include "llvm/IR/Operator.h"
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCExpr.h"
+#include "llvm/MC/MCSectionCOFF.h"
 #include "llvm/MC/MCSectionELF.h"
 #include "llvm/Support/Dwarf.h"
 #include "llvm/Target/TargetLowering.h"
@@ -106,3 +108,62 @@ const MCExpr *X86WindowsTargetObjectFile::getExecutableRelativeSymbol(
                                  MCSymbolRefExpr::VK_COFF_IMGREL32,
                                  getContext());
 }
+
+static std::string APIntToHexString(const APInt &AI, unsigned Width) {
+  std::string HexString = utohexstr(AI.getLimitedValue(), /*LowerCase=*/true);
+  unsigned Size = HexString.size();
+  assert(Width >= Size && "hex string is too large!");
+  HexString.insert(HexString.begin(), Width - Size, '0');
+
+  return HexString;
+}
+
+
+static std::string scalarConstantToHexString(const Constant *C) {
+  Type *Ty = C->getType();
+  if (Ty->isFloatTy()) {
+    const auto *CFP = cast<ConstantFP>(C);
+    return APIntToHexString(CFP->getValueAPF().bitcastToAPInt(), /*Width=*/8);
+  } else if (Ty->isDoubleTy()) {
+    const auto *CFP = cast<ConstantFP>(C);
+    return APIntToHexString(CFP->getValueAPF().bitcastToAPInt(), /*Width=*/16);
+  } else if (const auto *ITy = dyn_cast<IntegerType>(Ty)) {
+    const auto *CI = cast<ConstantInt>(C);
+    return APIntToHexString(CI->getValue(), (ITy->getBitWidth() / 8) * 2);
+  }
+  llvm_unreachable("unexpected constant pool element type!");
+}
+
+const MCSection *
+X86WindowsTargetObjectFile::getSectionForConstant(SectionKind Kind,
+                                                  const Constant *C) const {
+  if (Kind.isReadOnly()) {
+    if (C) {
+      Type *Ty = C->getType();
+      SmallString<32> COMDATSymName;
+      if (Ty->isFloatTy() || Ty->isDoubleTy()) {
+        COMDATSymName = "__real@";
+        COMDATSymName += scalarConstantToHexString(C);
+      } else if (const auto *VTy = dyn_cast<VectorType>(Ty)) {
+        uint64_t NumBits = VTy->getBitWidth();
+        if (NumBits == 128 || NumBits == 256) {
+          const auto *CDV = cast<ConstantDataVector>(C);
+          COMDATSymName = NumBits == 128 ? "__xmm@" : "__ymm@";
+          for (int I = CDV->getNumElements() - 1, E = -1; I != E; --I)
+            COMDATSymName +=
+                scalarConstantToHexString(CDV->getElementAsConstant(I));
+        }
+      }
+      if (!COMDATSymName.empty()) {
+        unsigned Characteristics = COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
+                                   COFF::IMAGE_SCN_MEM_READ |
+                                   COFF::IMAGE_SCN_LNK_COMDAT;
+        return getContext().getCOFFSection(".rdata", Characteristics, Kind,
+                                           COMDATSymName,
+                                           COFF::IMAGE_COMDAT_SELECT_ANY);
+      }
+    }
+  }
+
+  return TargetLoweringObjectFile::getSectionForConstant(Kind, C);
+}
diff --git a/llvm/lib/Target/X86/X86TargetObjectFile.h b/llvm/lib/Target/X86/X86TargetObjectFile.h
index a08ed09ffb9..4a10b7ea6b4 100644
--- a/llvm/lib/Target/X86/X86TargetObjectFile.h
+++ b/llvm/lib/Target/X86/X86TargetObjectFile.h
@@ -46,6 +46,11 @@ namespace llvm {
     const MCExpr *
     getExecutableRelativeSymbol(const ConstantExpr *CE, Mangler &Mang,
                                 const TargetMachine &TM) const override;
+
+    /// \brief Given a mergeable constant with the specified size and relocation
+    /// information, return a section that it should be placed in.
+    const MCSection *getSectionForConstant(SectionKind Kind,
+                                           const Constant *C) const override;
   };
 
 } // end namespace llvm
diff --git a/llvm/lib/Target/XCore/XCoreTargetObjectFile.cpp b/llvm/lib/Target/XCore/XCoreTargetObjectFile.cpp
index ab0f7ad47dc..cfd3302481e 100644
--- a/llvm/lib/Target/XCore/XCoreTargetObjectFile.cpp
+++ b/llvm/lib/Target/XCore/XCoreTargetObjectFile.cpp
@@ -165,8 +165,9 @@ SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
   report_fatal_error("Target does not support TLS or Common sections");
 }
 
-const MCSection *XCoreTargetObjectFile::
-getSectionForConstant(SectionKind Kind) const {
+const MCSection *
+XCoreTargetObjectFile::getSectionForConstant(SectionKind Kind,
+                                             const Constant *C) const {
   if (Kind.isMergeableConst4())           return MergeableConst4Section;
   if (Kind.isMergeableConst8())           return MergeableConst8Section;
   if (Kind.isMergeableConst16())          return MergeableConst16Section;
diff --git a/llvm/lib/Target/XCore/XCoreTargetObjectFile.h b/llvm/lib/Target/XCore/XCoreTargetObjectFile.h
index 34d756edc3f..d389e55ae39 100644
--- a/llvm/lib/Target/XCore/XCoreTargetObjectFile.h
+++ b/llvm/lib/Target/XCore/XCoreTargetObjectFile.h
@@ -34,7 +34,8 @@ static const unsigned CodeModelLargeSize = 256;
                              Mangler &Mang,
                              const TargetMachine &TM) const override;
 
-    const MCSection *getSectionForConstant(SectionKind Kind) const override;
+    const MCSection *getSectionForConstant(SectionKind Kind,
+                                           const Constant *C) const override;
   };
 } // end namespace llvm