[mips] Add the following MIPS options that control gp-relative addressing of

small data items: -mgpopt, -mlocal-sdata, -mextern-sdata. Implement gp-relative
addressing for constants.

Differential Revision: http://reviews.llvm.org/D4903

llvm-svn: 221450

1 files changed, 57 insertions, 13 deletions

diff --git a/llvm/lib/Target/Mips/MipsTargetObjectFile.cpp b/llvm/lib/Target/Mips/MipsTargetObjectFile.cpp
index 82c9fe9..b56c39b 100644
--- a/llvm/lib/Target/Mips/MipsTargetObjectFile.cpp
+++ b/llvm/lib/Target/Mips/MipsTargetObjectFile.cpp
@@ -24,6 +24,17 @@ SSThreshold("mips-ssection-threshold", cl::Hidden,
             cl::desc("Small data and bss section threshold size (default=8)"),
             cl::init(8));
 
+static cl::opt<bool>
+LocalSData("mlocal-sdata", cl::Hidden,
+           cl::desc("MIPS: Use gp_rel for object-local data."),
+           cl::init(true));
+
+static cl::opt<bool>
+ExternSData("mextern-sdata", cl::Hidden,
+            cl::desc("MIPS: Use gp_rel for data that is not defined by the "
+                     "current object."),
+            cl::init(true));
+
 void MipsTargetObjectFile::Initialize(MCContext &Ctx, const TargetMachine &TM){
   TargetLoweringObjectFileELF::Initialize(Ctx, TM);
   InitializeELF(TM.Options.UseInitArray);
@@ -37,29 +48,46 @@ void MipsTargetObjectFile::Initialize(MCContext &Ctx, const TargetMachine &TM){
     getContext().getELFSection(".sbss", ELF::SHT_NOBITS,
                                ELF::SHF_WRITE |ELF::SHF_ALLOC,
                                SectionKind::getBSS());
+  this->TM = &TM;
 }
 
 // A address must be loaded from a small section if its size is less than the
 // small section size threshold. Data in this section must be addressed using
 // gp_rel operator.
 static bool IsInSmallSection(uint64_t Size) {
+  // gcc has traditionally not treated zero-sized objects as small data, so this
+  // is effectively part of the ABI.
   return Size > 0 && Size <= SSThreshold;
 }
 
-bool MipsTargetObjectFile::IsGlobalInSmallSection(const GlobalValue *GV,
-                                                const TargetMachine &TM) const {
+/// Return true if this global address should be placed into small data/bss
+/// section.
+bool MipsTargetObjectFile::
+IsGlobalInSmallSection(const GlobalValue *GV, const TargetMachine &TM) const {
+  // We first check the case where global is a declaration, because finding
+  // section kind using getKindForGlobal() is only allowed for global
+  // definitions.
   if (GV->isDeclaration() || GV->hasAvailableExternallyLinkage())
-    return false;
+    return IsGlobalInSmallSectionImpl(GV, TM);
 
   return IsGlobalInSmallSection(GV, TM, getKindForGlobal(GV, TM));
 }
 
-/// IsGlobalInSmallSection - Return true if this global address should be
-/// placed into small data/bss section.
+/// Return true if this global address should be placed into small data/bss
+/// section.
 bool MipsTargetObjectFile::
 IsGlobalInSmallSection(const GlobalValue *GV, const TargetMachine &TM,
                        SectionKind Kind) const {
+  return (IsGlobalInSmallSectionImpl(GV, TM) &&
+          (Kind.isDataRel() || Kind.isBSS() || Kind.isCommon()));
+}
 
+/// Return true if this global address should be placed into small data/bss
+/// section. This method does all the work, except for checking the section
+/// kind.
+bool MipsTargetObjectFile::
+IsGlobalInSmallSectionImpl(const GlobalValue *GV,
+                           const TargetMachine &TM) const {
   const MipsSubtarget &Subtarget = TM.getSubtarget<MipsSubtarget>();
 
   // Return if small section is not available.
@@ -71,13 +99,13 @@ IsGlobalInSmallSection(const GlobalValue *GV, const TargetMachine &TM,
   if (!GVA)
     return false;
 
-  // We can only do this for datarel or BSS objects for now.
-  if (!Kind.isBSS() && !Kind.isDataRel())
+  // Enforce -mlocal-sdata.
+  if (!LocalSData && GV->hasLocalLinkage())
     return false;
 
-  // If this is a internal constant string, there is a special
-  // section for it, but not in small data/bss.
-  if (Kind.isMergeable1ByteCString())
+  // Enforce -mextern-sdata.
+  if (!ExternSData && ((GV->hasExternalLinkage() && GV->isDeclaration()) ||
+                       GV->hasCommonLinkage()))
     return false;
 
   Type *Ty = GV->getType()->getElementType();
@@ -85,8 +113,6 @@ IsGlobalInSmallSection(const GlobalValue *GV, const TargetMachine &TM,
       TM.getSubtargetImpl()->getDataLayout()->getTypeAllocSize(Ty));
 }
 
-
-
 const MCSection *MipsTargetObjectFile::
 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
                        Mangler &Mang, const TargetMachine &TM) const {
@@ -96,9 +122,27 @@ SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
   // Handle Small Section classification here.
   if (Kind.isBSS() && IsGlobalInSmallSection(GV, TM, Kind))
     return SmallBSSSection;
-  if (Kind.isDataNoRel() && IsGlobalInSmallSection(GV, TM, Kind))
+  if (Kind.isDataRel() && IsGlobalInSmallSection(GV, TM, Kind))
     return SmallDataSection;
 
   // Otherwise, we work the same as ELF.
   return TargetLoweringObjectFileELF::SelectSectionForGlobal(GV, Kind, Mang,TM);
 }
+
+/// Return true if this constant should be placed into small data section.
+bool MipsTargetObjectFile::
+IsConstantInSmallSection(const Constant *CN, const TargetMachine &TM) const {
+  return (TM.getSubtarget<MipsSubtarget>().useSmallSection() &&
+          LocalSData &&
+          IsInSmallSection(TM.getSubtargetImpl()->getDataLayout()
+                           ->getTypeAllocSize(CN->getType())));
+}
+
+const MCSection *MipsTargetObjectFile::
+getSectionForConstant(SectionKind Kind, const Constant *C) const {
+  if (IsConstantInSmallSection(C, *TM))
+    return SmallDataSection;
+
+  // Otherwise, we work the same as ELF.
+  return TargetLoweringObjectFileELF::getSectionForConstant(Kind, C);
+}