Enable assembly output of local commons for AIX

Summary:
This patch enable assembly output of local commons for AIX using .lcomm
directives. Adds a EmitXCOFFLocalCommonSymbol to MCStreamer so we can emit the
AIX version of .lcomm assembly directives which include a csect name. Handle the
case of BSS locals in PPCAIXAsmPrinter by using EmitXCOFFLocalCommonSymbol. Adds
a test for generating .lcomm on AIX Targets.

Reviewers: cebowleratibm, hubert.reinterpretcast, Xiangling_L, jasonliu, sfertile

Reviewed By: sfertile

Subscribers: wuzish, nemanjai, hiraditya, kbarton, MaskRay, jsji, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D64825

llvm-svn: 368306

include/llvm/MC/MCStreamer.h

@@ -537,6 +537,15 @@ public:
   /// \param Symbol - Symbol the image relative relocation should point to.
   virtual void EmitCOFFImgRel32(MCSymbol const *Symbol, int64_t Offset);
 
+  /// Emits an lcomm directive with XCOFF csect information.
+  ///
+  /// \param Symbol - The symbol we are emiting.
+  /// \param Size - The size of the block of storage.
+  /// \param ByteAlignment - The alignment of the symbol in bytes. Must be a power
+  /// of 2.
+  virtual void EmitXCOFFLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
+                             unsigned ByteAlignment);
+
   /// Emit an ELF .size directive.
   ///
   /// This corresponds to an assembler statement such as:

include/llvm/MC/MCXCOFFStreamer.h

@@ -26,6 +26,8 @@ public:
                     uint64_t Size = 0, unsigned ByteAlignment = 0,
                     SMLoc Loc = SMLoc()) override;
   void EmitInstToData(const MCInst &Inst, const MCSubtargetInfo &) override;
+  void EmitXCOFFLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
+                                  unsigned ByteAlign) override;
 };
 
 } // end namespace llvm

lib/CodeGen/TargetLoweringObjectFileImpl.cpp

@@ -1836,11 +1836,12 @@ MCSection *TargetLoweringObjectFileXCOFF::SelectSectionForGlobal(
 
   // Common symbols go into a csect with matching name which will get mapped
   // into the .bss section.
-  if (Kind.isCommon()) {
+  if (Kind.isBSSLocal() || Kind.isCommon()) {
     SmallString<128> Name;
     getNameWithPrefix(Name, GO, TM);
-    return getContext().getXCOFFSection(Name, XCOFF::XMC_RW, XCOFF::XTY_CM,
-                                        Kind, /* BeginSymbolName */ nullptr);
+    return getContext().getXCOFFSection(
+        Name, Kind.isBSSLocal() ? XCOFF::XMC_BS : XCOFF::XMC_RW, XCOFF::XTY_CM,
+        Kind, /* BeginSymbolName */ nullptr);
   }
 
   if (Kind.isText())

lib/MC/MCAsmInfoXCOFF.cpp

@@ -16,4 +16,5 @@ MCAsmInfoXCOFF::MCAsmInfoXCOFF() {
   IsLittleEndian = false;
   HasDotTypeDotSizeDirective = false;
   COMMDirectiveAlignmentIsInBytes = false;
+  LCOMMDirectiveAlignmentType = LCOMM::Log2Alignment;
 }

lib/MC/MCAsmStreamer.cpp

@@ -162,6 +162,8 @@ public:
   void EmitCOFFSectionIndex(MCSymbol const *Symbol) override;
   void EmitCOFFSecRel32(MCSymbol const *Symbol, uint64_t Offset) override;
   void EmitCOFFImgRel32(MCSymbol const *Symbol, int64_t Offset) override;
+  void EmitXCOFFLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
+                                  unsigned ByteAlign) override;
   void emitELFSize(MCSymbol *Symbol, const MCExpr *Value) override;
   void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                         unsigned ByteAlignment) override;
@@ -757,6 +759,24 @@ void MCAsmStreamer::EmitCOFFImgRel32(MCSymbol const *Symbol, int64_t Offset) {
   EmitEOL();
 }
 
+// We need an XCOFF specific version of this directive as the AIX syntax
+// requires a QualName argument identifying the csect name and storage mapping
+// class to appear before the alignment if we are specifying it.
+void MCAsmStreamer::EmitXCOFFLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
+                                               unsigned ByteAlignment) {
+  assert(MAI->getLCOMMDirectiveAlignmentType() == LCOMM::Log2Alignment &&
+         "We only support writing log base-2 alignment format with XCOFF");
+  assert(isPowerOf2_32(ByteAlignment) && "alignment must be a power of 2");
+
+  OS << "\t.lcomm\t";
+  Symbol->print(OS, MAI);
+  OS << ',' << Size;
+  OS << ',' << Symbol->getName();
+  OS << ',' << Log2_32(ByteAlignment);
+
+  EmitEOL();
+}
+
 void MCAsmStreamer::emitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
   assert(MAI->hasDotTypeDotSizeDirective());
   OS << "\t.size\t";

lib/MC/MCSectionXCOFF.cpp

@@ -28,9 +28,11 @@ void MCSectionXCOFF::PrintSwitchToSection(const MCAsmInfo &MAI, const Triple &T,
     return;
   }
 
-  if (getKind().isCommon()) {
-    if (getMappingClass() != XCOFF::XMC_RW)
-      llvm_unreachable("Unsupported storage-mapping class for common csect");
+  if (getKind().isBSSLocal() || getKind().isCommon()) {
+    if (getMappingClass() != XCOFF::XMC_RW &&
+        getMappingClass() != XCOFF::XMC_BS)
+      llvm_unreachable("Generated a storage-mapping class for a common/bss "
+                       "csect we don't understand how to switch to.");
     if (getCSectType() != XCOFF::XTY_CM)
       llvm_unreachable("wrong csect type for .bss csect");
     // Don't have to print a directive for switching to section for commons.

lib/MC/MCStreamer.cpp

@@ -1055,6 +1055,10 @@ void MCStreamer::EmitCOFFSymbolStorageClass(int StorageClass) {
 void MCStreamer::EmitCOFFSymbolType(int Type) {
   llvm_unreachable("this directive only supported on COFF targets");
 }
+void MCStreamer::EmitXCOFFLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
+                                            unsigned ByteAlign) {
+  llvm_unreachable("this directive only supported on XCOFF targets");
+}
 void MCStreamer::emitELFSize(MCSymbol *Symbol, const MCExpr *Value) {}
 void MCStreamer::emitELFSymverDirective(StringRef AliasName,
                                         const MCSymbol *Aliasee) {}

lib/MC/MCXCOFFStreamer.cpp

@@ -57,3 +57,8 @@ MCStreamer *llvm::createXCOFFStreamer(MCContext &Context,
     S->getAssembler().setRelaxAll(true);
   return S;
 }
+
+void MCXCOFFStreamer::EmitXCOFFLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
+                                            unsigned ByteAlign) {
+  llvm_unreachable("Not implemented yet.");
+}

lib/Target/PowerPC/PPCAsmPrinter.cpp

@@ -1659,7 +1659,7 @@ void PPCAIXAsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
     report_fatal_error("COMDAT not yet supported by AIX.");
 
   SectionKind GVKind = getObjFileLowering().getKindForGlobal(GV, TM);
-  if (!GVKind.isCommon())
+  if (!GVKind.isCommon() && !GVKind.isBSSLocal())
     report_fatal_error("Only common variables are supported on AIX for now.");
 
   // Create the containing csect and switch to it.
@@ -1673,7 +1673,11 @@ void PPCAIXAsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
   unsigned Align =
       GV->getAlignment() ? GV->getAlignment() : DL.getPreferredAlignment(GV);
   uint64_t Size = DL.getTypeAllocSize(GV->getType()->getElementType());
-  OutStreamer->EmitCommonSymbol(XSym, Size, Align);
+
+  if (GVKind.isBSSLocal())
+    OutStreamer->EmitXCOFFLocalCommonSymbol(XSym, Size, Align);
+  else
+    OutStreamer->EmitCommonSymbol(XSym, Size, Align);
 }
 
 /// createPPCAsmPrinterPass - Returns a pass that prints the PPC assembly code

test/CodeGen/PowerPC/aix-xcoff-lcomm.ll

@@ -0,0 +1,10 @@
+; RUN: llc -mtriple powerpc-ibm-aix-xcoff < %s | FileCheck %s
+; RUN: llc -mtriple powerpc64-ibm-aix-xcoff < %s | FileCheck %s
+
+@a = internal global i32 0, align 4
+@b = internal global i64 0, align 8
+@c = internal global i16 0, align 2
+
+; CHECK:      .lcomm a,4,a,2
+; CHECK-NEXT: .lcomm b,8,b,3
+; CHECK-NEXT: .lcomm c,2,c,1