[mips] Support -membedded-data and fix a related bug

[sdardis]

Summary

-membedded-data changes the location of constant data from the .sdata to
the .rodata section. Previously it was (incorrectly) always located in the
.rodata section.

[atanasyan]

LGTM with minor nits.

lib/Target/Mips/MipsTargetObjectFile.cpp

158

Do we really need this comment? Its meaning is not obvious.

[sdardis]

lib/Target/Mips/MipsTargetObjectFile.cpp

158

Hm, left over code from development. I'll remove before committing.

[sdardis]

Address review comment.

[atanasyan]

Feel free to commit the patch.

lib/Target/Mips/MipsTargetObjectFile.cpp

LocalSData("mlocal-sdata", cl::Hidden,
            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));
 
+static cl::opt<bool>
+EmbeddedData("membedded-data", cl::Hidden,
+             cl::desc("MIPS: Try to allocate variables in the following"
+                      " sections if possible: .rodata, .sdata, .data ."),
+             cl::init(false));
+
 void MipsTargetObjectFile::Initialize(MCContext &Ctx, const TargetMachine &TM){
   TargetLoweringObjectFileELF::Initialize(Ctx, TM);
   InitializeELF(TM.Options.UseInitArray);
 
   SmallDataSection = getContext().getELFSection(
       ".sdata", ELF::SHT_PROGBITS,
       ELF::SHF_WRITE | ELF::SHF_ALLOC | ELF::SHF_MIPS_GPREL);
 
bool MipsTargetObjectFile::IsGlobalInSmallSection(
   return IsGlobalInSmallSection(GO, TM, getKindForGlobal(GO, TM));
 }
 
 /// Return true if this global address should be placed into small data/bss
 /// section.
 bool MipsTargetObjectFile::
 IsGlobalInSmallSection(const GlobalObject *GO, const TargetMachine &TM,
                        SectionKind Kind) const {
-  return (IsGlobalInSmallSectionImpl(GO, TM) &&
-          (Kind.isData() || Kind.isBSS() || Kind.isCommon()));
+  return IsGlobalInSmallSectionImpl(GO, TM) &&
+         (Kind.isData() || Kind.isBSS() || Kind.isCommon() ||
+          Kind.isReadOnly());
 }
 
 /// 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 GlobalObject *GO,
                            const TargetMachine &TM) const {
IsGlobalInSmallSectionImpl(const GlobalObject *GO,
   if (!LocalSData && GVA->hasLocalLinkage())
     return false;
 
   // Enforce -mextern-sdata.
   if (!ExternSData && ((GVA->hasExternalLinkage() && GVA->isDeclaration()) ||
                        GVA->hasCommonLinkage()))
     return false;
 
+  // Enforce -membedded-data.
+  if (EmbeddedData && GVA->isConstant())
+    return false;
+
   Type *Ty = GVA->getValueType();
   return IsInSmallSection(
       GVA->getParent()->getDataLayout().getTypeAllocSize(Ty));
 }
 
 MCSection *MipsTargetObjectFile::SelectSectionForGlobal(
     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
   // TODO: Could also support "weak" symbols as well with ".gnu.linkonce.s.*"
   // sections?
 
   // Handle Small Section classification here.
   if (Kind.isBSS() && IsGlobalInSmallSection(GO, TM, Kind))
     return SmallBSSSection;
   if (Kind.isData() && IsGlobalInSmallSection(GO, TM, Kind))
     return SmallDataSection;
+  if (Kind.isReadOnly() && IsGlobalInSmallSection(GO, TM, Kind))
+    return SmallDataSection;
 
   // Otherwise, we work the same as ELF.
   return TargetLoweringObjectFileELF::SelectSectionForGlobal(GO, Kind, TM);
 }
 
 /// Return true if this constant should be placed into small data section.
 bool MipsTargetObjectFile::IsConstantInSmallSection(
     const DataLayout &DL, const Constant *CN, const TargetMachine &TM) const {
   return (static_cast<const MipsTargetMachine &>(TM)
               .getSubtargetImpl()
               ->useSmallSection() &&
           LocalSData && IsInSmallSection(DL.getTypeAllocSize(CN->getType())));
 }
 
 /// Return true if this constant should be placed into small data section.
 MCSection *MipsTargetObjectFile::getSectionForConstant(const DataLayout &DL,
                                                        SectionKind Kind,
                                                        const Constant *C,
                                                        unsigned &Align) const {
   if (IsConstantInSmallSection(DL, C, *TM))
     return SmallDataSection;
 
   // Otherwise, we work the same as ELF.
   return TargetLoweringObjectFileELF::getSectionForConstant(DL, Kind, C, Align);
 }
 
 const MCExpr *
 MipsTargetObjectFile::getDebugThreadLocalSymbol(const MCSymbol *Sym) const {
   const MCExpr *Expr =
       MCSymbolRefExpr::create(Sym, MCSymbolRefExpr::VK_None, getContext());
   return MCBinaryExpr::createAdd(
       Expr, MCConstantExpr::create(0x8000, getContext()), getContext());
 }

test/CodeGen/Mips/2008-07-15-SmallSection.ll

-; RUN: llc < %s -march=mips -mcpu=mips32 -mips-ssection-threshold=8 -relocation-model=static -mattr=+noabicalls -mgpopt | FileCheck %s
+; RUN: llc < %s -march=mips -mcpu=mips32 -mips-ssection-threshold=8 \
+; RUN:     -relocation-model=static -mattr=+noabicalls -mgpopt \
+; RUN:   | FileCheck %s --check-prefixes=BASIC,COMMON
+; RUN: llc < %s -march=mips -mcpu=mips32 -mips-ssection-threshold=8 \
+; RUN:     -relocation-model=static -mattr=+noabicalls -mgpopt -membedded-data \
+; RUN:   | FileCheck %s --check-prefixes=EMBDATA,COMMON
+
+; Test the layout of objects when compiling for static, noabicalls environment.
 
 %struct.anon = type { i32, i32 }
 
+; BASIC: .type  s0,@object
+; BASIC-NEXT: .section .sdata,"aw",@progbits
+
+; EMDATA: .type  s0,@object
+; EMDATA-NEXT: .section .rodata,"a",@progbits
+
 @s0 = constant [8 x i8] c"AAAAAAA\00", align 4
 
-; CHECK: .type  foo,@object
-; CHECK-NEXT: .section .sdata,"aw",@progbits
+; BASIC: .type  foo,@object
+; BASIC-NOT:  .section
+
+; EMBDATA: .type  foo,@object
+; EMBDATA-NEXT:  .section .sdata,"aw",@progbits
 @foo = global %struct.anon { i32 2, i32 3 }
 
-; CHECK:  .type bar,@object
-; CHECK-NEXT:  .section  .sbss,"aw",@nobits
-@bar = global %struct.anon zeroinitializer 
+; COMMON:  .type bar,@object
+; COMMON-NEXT:  .section  .sbss,"aw",@nobits
+@bar = global %struct.anon zeroinitializer
 
 define i8* @A0() nounwind {
 entry:
   ret i8* getelementptr ([8 x i8], [8 x i8]* @s0, i32 0, i32 0)
 }
 
 define i32 @A1() nounwind {
 entry:
   load i32, i32* getelementptr (%struct.anon, %struct.anon* @foo, i32 0, i32 0), align 8 
   load i32, i32* getelementptr (%struct.anon, %struct.anon* @foo, i32 0, i32 1), align 4 
   add i32 %1, %0
   ret i32 %2
 }