[PowerPC] Emit gnu_attribute according to float-abi metadata

[qiucf]

Summary

According to GNU as documentation, PowerPC supports two kinds of .gnu_attribute tag to represent the vector and float ABI type in the object file. (https://sourceware.org/binutils/docs-2.35/as/GNU-Object-Attributes.html) Some linkers like GNU ld respects the attribute and will prevent objects with conflicting ABIs being linked.

This patch emits gnu_attribute value in assembly printer according to the float-abi metadata defined in D116016.

[jsji]

LGTM with some nits.

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

181

Should we name it emitGNUAttributes? or even emitGNUAttributes_ABI_FP

1400

Can we avoid the magic number here? 4 should be Tag_GNU_Power_ABI_FP.

and define:

Val_GNU_Power_ABI_No_Float 0b00
Val_GNU_Power_ABI_HardFloat_DP 0b01
Val_GNU_Power_ABI_SoftFloat_DP 0b02
Val_GNU_Power_ABI_HardFloat_SP 0b03

Val_GNU_Power_ABI_LDBL_IBM128 0b0100
Val_GNU_Power_ABI_LDBL_64 0b1000
Val_GNU_Power_ABI_LDBL_IEEE128 0b1100

then 5 should be
Val_GNU_Power_ABI_HardFloat_DP | Val_GNU_Power_ABI_LDBL_IBM128

9 should be:
Val_GNU_Power_ABI_HardFloat_DP | Val_GNU_Power_ABI_LDBL_64

13 should be:
Val_GNU_Power_ABI_HardFloat_DP | Val_GNU_Power_ABI_LDBL_IEEE128

llvm/test/CodeGen/PowerPC/gnu-attribute.ll

5

How about softfp?

[qiucf]

llvm/test/CodeGen/PowerPC/gnu-attribute.ll

5

Emitting attributes for softfp is not supported yet. Currently soft/hard fp info is stored in function attrs instead of module flags. We'll need to pass extra info from clang. Make it a TODO here.

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

return detail::combineHashValue(
         DenseMapInfo<int>::getHashValue(PairVal.second));
   }
   static bool isEqual(const TOCKey &A, const TOCKey &B) { return A == B; }
 };
 } // end namespace llvm
 
 namespace {
 
+enum {
+  // GNU attribute tags for PowerPC ABI
+  Tag_GNU_Power_ABI_FP = 4,
+  Tag_GNU_Power_ABI_Vector = 8,
+  Tag_GNU_Power_ABI_Struct_Return = 12,
+
+  // GNU attribute values for PowerPC float ABI, as combination of two parts
+  Val_GNU_Power_ABI_NoFloat = 0b00,
+  Val_GNU_Power_ABI_HardFloat_DP = 0b01,
+  Val_GNU_Power_ABI_SoftFloat_DP = 0b10,
+  Val_GNU_Power_ABI_HardFloat_SP = 0b11,
+
+  Val_GNU_Power_ABI_LDBL_IBM128 = 0b0100,
+  Val_GNU_Power_ABI_LDBL_64 = 0b1000,
+  Val_GNU_Power_ABI_LDBL_IEEE128 = 0b1100,
+};
+
 class PPCAsmPrinter : public AsmPrinter {
 protected:
   // For TLS on AIX, we need to be able to identify TOC entries of specific
   // VariantKind so we can add the right relocations when we generate the
   // entries. So each entry is represented by a pair of MCSymbol and
   // VariantKind. For example, we need to be able to identify the following
   // entry as a TLSGD entry so we can add the @m relocation:
   //   .tc .i[TC],i[TL]@m
public:
 
   void emitEndOfAsmFile(Module &M) override;
 
   void LowerSTACKMAP(StackMaps &SM, const MachineInstr &MI);
   void LowerPATCHPOINT(StackMaps &SM, const MachineInstr &MI);
   void EmitTlsCall(const MachineInstr *MI, MCSymbolRefExpr::VariantKind VK);
   bool runOnMachineFunction(MachineFunction &MF) override {
     Subtarget = &MF.getSubtarget<PPCSubtarget>();
     bool Changed = AsmPrinter::runOnMachineFunction(MF);
     emitXRayTable();
     return Changed;
   }
 };
 
 /// PPCLinuxAsmPrinter - PowerPC assembly printer, customized for Linux
 class PPCLinuxAsmPrinter : public PPCAsmPrinter {
 public:
   explicit PPCLinuxAsmPrinter(TargetMachine &TM,
                               std::unique_ptr<MCStreamer> Streamer)
       : PPCAsmPrinter(TM, std::move(Streamer)) {}
 
   StringRef getPassName() const override {
     return "Linux PPC Assembly Printer";
   }
 
+  void emitGNUAttributes(Module &M);
+
   void emitStartOfAsmFile(Module &M) override;
   void emitEndOfAsmFile(Module &) override;
 
   void emitFunctionEntryLabel() override;
 
   void emitFunctionBodyStart() override;
   void emitFunctionBodyEnd() override;
   void emitInstruction(const MachineInstr *MI) override;
case PPC::LWA: {
     break;
   }
   case PPC::PseudoEIEIO: {
     EmitToStreamer(
         *OutStreamer,
         MCInstBuilder(PPC::ORI).addReg(PPC::X2).addReg(PPC::X2).addImm(0));
     EmitToStreamer(
         *OutStreamer,
         MCInstBuilder(PPC::ORI).addReg(PPC::X2).addReg(PPC::X2).addImm(0));
     EmitToStreamer(*OutStreamer, MCInstBuilder(PPC::EnforceIEIO));
     return;
   }
   }
 
   LowerPPCMachineInstrToMCInst(MI, TmpInst, *this);
   EmitToStreamer(*OutStreamer, TmpInst);
 }
 
+void PPCLinuxAsmPrinter::emitGNUAttributes(Module &M) {
+  // Emit float ABI into GNU attribute
+  Metadata *MD = M.getModuleFlag("float-abi");
+  MDString *FloatABI = dyn_cast_or_null<MDString>(MD);
+  if (!FloatABI)
+    return;
+  StringRef flt = FloatABI->getString();
+  // TODO: Support emitting soft-fp and hard double/single attributes.
+  if (flt == "doubledouble")
+    OutStreamer->emitGNUAttribute(Tag_GNU_Power_ABI_FP,
+                                  Val_GNU_Power_ABI_HardFloat_DP |
+                                      Val_GNU_Power_ABI_LDBL_IBM128);
+  else if (flt == "ieeequad")
+    OutStreamer->emitGNUAttribute(Tag_GNU_Power_ABI_FP,
+                                  Val_GNU_Power_ABI_HardFloat_DP |
+                                      Val_GNU_Power_ABI_LDBL_IEEE128);
+  else if (flt == "ieeedouble")
+    OutStreamer->emitGNUAttribute(Tag_GNU_Power_ABI_FP,
+                                  Val_GNU_Power_ABI_HardFloat_DP |
+                                      Val_GNU_Power_ABI_LDBL_64);
+}
+
 void PPCLinuxAsmPrinter::emitInstruction(const MachineInstr *MI) {
   if (!Subtarget->isPPC64())
     return PPCAsmPrinter::emitInstruction(MI);
 
   switch (MI->getOpcode()) {
   default:
     return PPCAsmPrinter::emitInstruction(MI);
   case TargetOpcode::PATCHABLE_FUNCTION_ENTER: {

 void PPCLinuxAsmPrinter::emitEndOfAsmFile(Module &M) {
   const DataLayout &DL = getDataLayout();
 
   bool isPPC64 = DL.getPointerSizeInBits() == 64;
 
   PPCTargetStreamer *TS =
       static_cast<PPCTargetStreamer *>(OutStreamer->getTargetStreamer());
 
+  emitGNUAttributes(M);
+
   if (!TOC.empty()) {
     const char *Name = isPPC64 ? ".toc" : ".got2";
     MCSectionELF *Section = OutContext.getELFSection(
         Name, ELF::SHT_PROGBITS, ELF::SHF_WRITE | ELF::SHF_ALLOC);
     OutStreamer->SwitchSection(Section);
     if (!isPPC64)
       OutStreamer->emitValueToAlignment(4);
 

llvm/test/CodeGen/PowerPC/gnu-attribute.ll

+; RUN: sed -e 's/FLTABI/ieeequad/' %s | llc -mtriple=powerpc64le | FileCheck %s --check-prefix=IEEE
+; RUN: sed -e 's/FLTABI/doubledouble/' %s | llc -mtriple=powerpc64le | FileCheck %s --check-prefix=IBM
+; RUN: sed -e 's/FLTABI/ieeedouble/' %s | llc -mtriple=powerpc64le | FileCheck %s --check-prefix=DBL
+; RUN: sed -e 's/FLTABI//' %s | llc -mtriple=powerpc64le | FileCheck %s --check-prefix=NONE
+
+; IEEE: .gnu_attribute 4, 13
+; IBM: .gnu_attribute 4, 5
+; DBL: .gnu_attribute 4, 9
+; NONE-NOT: .gnu_attribute 4,
+
+!llvm.module.flags = !{!0, !1, !2}
+
+!0 = !{i32 1, !"wchar_size", i32 4}
+!1 = !{i32 7, !"uwtable", i32 1}
+!2 = !{i32 1, !"float-abi", !"FLTABI"}