[AIX][XCOFF] rename metadata

llvm/docs/LangRef.rst

@@ -8441,6 +8441,29 @@ The ``nofree`` metadata indicates the memory pointed by the pointer will not be
 freed after the attached instruction.
 
 
+'``rename.key``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^
+The rename key may be attached to a global variable definition that has an
+explicit section attribute. It is used as a flag so the associated node
+must be empty. It only takes effect when function sections is enabled, and
+only on XCOFF targets. The metadata will casue the global to be emitted to a
+control section (CSECT) with a name that is an amalgamation of both the section
+attribute and the global variables identifier. After the control section is
+defined it will be renamed to match the name of the section attribute. This
+allows the linker to aggressively garbage collect the symbol if unreferenced,
+while directing the linker to merge any control sections with the same name
+that remain after garbage collecting into the same CSECT in the output binary.
+Commonly used where there is a feature that uses a runtime to walk over a
+section using the linker-defined encapsulation symbols
+``__start_<section_name>`` and ``__stop_<section_name>``.
+
+Example:
+
+.. code-block:: llvm
+
+    @a = global i32 1, section "abc", !rename.key !0
+    !0 = !{}
+
 Module Flags Metadata
 =====================
 

llvm/include/llvm/IR/FixedMetadataKinds.def

@@ -55,3 +55,4 @@ LLVM_FIXED_MD_KIND(MD_mmra, "mmra", 40)
 LLVM_FIXED_MD_KIND(MD_noalias_addrspace, "noalias.addrspace", 41)
 LLVM_FIXED_MD_KIND(MD_callee_type, "callee_type", 42)
 LLVM_FIXED_MD_KIND(MD_nofree, "nofree", 43)
+LLVM_FIXED_MD_KIND(MD_rename_key, "rename.key", 44)

llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp

@@ -2431,16 +2431,24 @@ MCSection *TargetLoweringObjectFileXCOFF::getExplicitSectionGlobal(
   if (!GO->hasSection())
     report_fatal_error("#pragma clang section is not yet supported");
 
-  StringRef SectionName = GO->getSection();
+  std::string SectionName(GO->getSection());
 
-  // Handle the XCOFF::TD case first, then deal with the rest.
-  if (const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GO))
+  // Have to check for either attributes or metadata that can affect the
+  // section type or section name.
+  if (const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GO)) {
     if (GVar->hasAttribute("toc-data"))
       return getContext().getXCOFFSection(
           SectionName, Kind,
           XCOFF::CsectProperties(/*MappingClass*/ XCOFF::XMC_TD, XCOFF::XTY_SD),
           /* MultiSymbolsAllowed*/ true);
 
+    if (TM.getFunctionSections() &&
+        GVar->hasMetadata(LLVMContext::MD_rename_key)) {
+      SectionName += ".";
+      SectionName += GO->getName();
+    }
+  }
+
   XCOFF::StorageMappingClass MappingClass;
   if (Kind.isText())
     MappingClass = XCOFF::XMC_PR;

llvm/lib/IR/Verifier.cpp

@@ -766,6 +766,15 @@ void Verifier::visitGlobalValue(const GlobalValue &GV) {
                               DL.getIntPtrType(GO->getType()),
                               RangeLikeMetadataKind::AbsoluteSymbol);
     }
+
+    if (GO->hasMetadata(LLVMContext::MD_rename_key)) {
+      SmallVector<MDNode *, 1> MDs;
+      GO->getMetadata(LLVMContext::MD_rename_key, MDs);
+      Check(MDs.size() == 1,
+            "global value cannot have more then 1 rename metadata", GO);
+      Check(MDs[0]->getNumOperands() == 0,
+            "rename metadata must have no operands", GO);
+    }
   }
 
   Check(!GV.hasAppendingLinkage() || isa<GlobalVariable>(GV),

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

@@ -2970,58 +2970,80 @@ void PPCAIXAsmPrinter::emitGCOVRefs() {
 }
 
 void PPCAIXAsmPrinter::emitEndOfAsmFile(Module &M) {
-  // If there are no functions and there are no toc-data definitions in this
-  // module, we will never need to reference the TOC base.
-  if (M.empty() && TOCDataGlobalVars.empty())
-    return;
 
   emitPGORefs(M);
   emitGCOVRefs();
 
-  // Switch to section to emit TOC base.
-  OutStreamer->switchSection(getObjFileLowering().getTOCBaseSection());
+  // If there are no functions and there are no toc-data definitions in this
+  // module, we will never need to reference the TOC base.
+  if (!M.empty() || !TOCDataGlobalVars.empty()) {
+    // Switch to section to emit TOC base.
+    OutStreamer->switchSection(getObjFileLowering().getTOCBaseSection());
 
-  PPCTargetStreamer *TS =
-      static_cast<PPCTargetStreamer *>(OutStreamer->getTargetStreamer());
+    PPCTargetStreamer *TS =
+        static_cast<PPCTargetStreamer *>(OutStreamer->getTargetStreamer());
+
+    for (auto &I : TOC) {
+      MCSectionXCOFF *TCEntry;
+      // Setup the csect for the current TC entry. If the variant kind is
+      // VK_AIX_TLSGDM the entry represents the region handle, we create a
+      // new symbol to prefix the name with a dot.
+      // If TLS model opt is turned on, create a new symbol to prefix the name
+      // with a dot.
+      if (I.first.second == PPC::S_AIX_TLSGDM ||
+          (Subtarget->hasAIXShLibTLSModelOpt() &&
+           I.first.second == PPC::S_AIX_TLSLD)) {
+        SmallString<128> Name;
+        StringRef Prefix = ".";
+        Name += Prefix;
+        Name += static_cast<const MCSymbolXCOFF *>(I.first.first)
+                    ->getSymbolTableName();
+        MCSymbol *S = OutContext.getOrCreateSymbol(Name);
+        TCEntry = static_cast<MCSectionXCOFF *>(
+            getObjFileLowering().getSectionForTOCEntry(S, TM));
+      } else {
+        TCEntry = static_cast<MCSectionXCOFF *>(
+            getObjFileLowering().getSectionForTOCEntry(I.first.first, TM));
+      }
+      OutStreamer->switchSection(TCEntry);
 
-  for (auto &I : TOC) {
-    MCSectionXCOFF *TCEntry;
-    // Setup the csect for the current TC entry. If the variant kind is
-    // VK_AIX_TLSGDM the entry represents the region handle, we create a
-    // new symbol to prefix the name with a dot.
-    // If TLS model opt is turned on, create a new symbol to prefix the name
-    // with a dot.
-    if (I.first.second == PPC::S_AIX_TLSGDM ||
-        (Subtarget->hasAIXShLibTLSModelOpt() &&
-         I.first.second == PPC::S_AIX_TLSLD)) {
-      SmallString<128> Name;
-      StringRef Prefix = ".";
-      Name += Prefix;
-      Name += static_cast<const MCSymbolXCOFF *>(I.first.first)
-                  ->getSymbolTableName();
-      MCSymbol *S = OutContext.getOrCreateSymbol(Name);
-      TCEntry = static_cast<MCSectionXCOFF *>(
-          getObjFileLowering().getSectionForTOCEntry(S, TM));
-    } else {
-      TCEntry = static_cast<MCSectionXCOFF *>(
-          getObjFileLowering().getSectionForTOCEntry(I.first.first, TM));
+      OutStreamer->emitLabel(I.second);
+      TS->emitTCEntry(*I.first.first, I.first.second);
     }
-    OutStreamer->switchSection(TCEntry);
 
-    OutStreamer->emitLabel(I.second);
-    TS->emitTCEntry(*I.first.first, I.first.second);
+    // Traverse the list of global variables twice, emitting all of the
+    // non-common global variables before the common ones, as emitting a
+    // .comm directive changes the scope from .toc to the common symbol.
+    for (const auto *GV : TOCDataGlobalVars) {
+      if (!GV->hasCommonLinkage())
+        emitGlobalVariableHelper(GV);
+    }
+    for (const auto *GV : TOCDataGlobalVars) {
+      if (GV->hasCommonLinkage())
+        emitGlobalVariableHelper(GV);
+    }
   }
 
-  // Traverse the list of global variables twice, emitting all of the
-  // non-common global variables before the common ones, as emitting a
-  // .comm directive changes the scope from .toc to the common symbol.
-  for (const auto *GV : TOCDataGlobalVars) {
-    if (!GV->hasCommonLinkage())
-      emitGlobalVariableHelper(GV);
-  }
-  for (const auto *GV : TOCDataGlobalVars) {
-    if (GV->hasCommonLinkage())
-      emitGlobalVariableHelper(GV);
+  // Renames only take effect when function sections is enabled.
+  if (!TM.getFunctionSections())
+    return;
+
+  for (const GlobalVariable &GV : M.globals()) {
+    if (GV.hasMetadata(LLVMContext::MD_rename_key)) {
+      // Get orginal csect.
+      SectionKind GVKind = getObjFileLowering().getKindForGlobal(&GV, TM);
+      auto *CSect = static_cast<MCSectionXCOFF *>(
+          getObjFileLowering().SectionForGlobal(&GV, GVKind, TM));
+
+      // Get the section to rename to.
+      if (!GV.hasSection())
+        reportFatalInternalError(
+            "rename.key metadata used without a section attribute");
+
+      StringRef SectionName = GV.getSection();
+      OutStreamer->emitXCOFFRenameDirective(CSect->getQualNameSymbol(),
+                                            SectionName);
+    }
   }
 }
 

llvm/test/CodeGen/PowerPC/aix-rename.ll

@@ -0,0 +1,38 @@
+; RUN: llc --function-sections -verify-machineinstrs -mtriple powerpc-ibm-aix-xcoff < %s | FileCheck %s
+; RUN: llc -verify-machineinstrs -mtriple powerpc-ibm-aix-xcoff < %s | FileCheck --check-prefix=NOFUNCSECT %s
+
+@a = global i32 1, section "abcd", !rename.key !0
+@b = global i32 2, section "abcd", !rename.key !0
+@c = global i32 3, section "abcd", !rename.key !0
+@d = global i32 4, section "abcd", !rename.key !0
+
+!0 = !{}
+
+;CHECK:     .csect abcd.a[RW]
+;CHECK:     .globl  a
+
+;CHECK:     .csect abcd.b[RW]
+;CHECK:     .globl  b
+
+;CHECK:     .csect abcd.c[RW]
+;CHECK:     .globl  c
+
+;CHECK:     .csect abcd.d[RW]
+;CHECK:     .globl  d
+
+;CHECK:     .rename abcd.a[RW],"abcd"
+;CHECK:     .rename abcd.b[RW],"abcd"
+;CHECK:     .rename abcd.c[RW],"abcd"
+;CHECK:     .rename abcd.d[RW],"abcd"
+
+;NOFUNCSECT:     .csect abcd[RW],2
+;NOFUNCSECT-NOT: .csect
+;NOFUNCSECT:     .globl  a
+;NOFUNCSECT-NOT: .csect
+;NOFUNCSECT:     .globl  b
+;NOFUNCSECT-NOT: .csect
+;NOFUNCSECT:     .globl  c
+;NOFUNCSECT-NOT: .csect
+;NOFUNCSECT:     .globl  d
+
+;NOFUNCSECT-NOT: .rename

llvm/test/Verifier/PowerPC/lit.local.cfg

@@ -0,0 +1,2 @@
+if not "PowerPC" in config.root.targets:
+    config.unsupported = True

llvm/test/Verifier/PowerPC/multiple_rename.ll

@@ -0,0 +1,8 @@
+; RUN: not llvm-as %s -o /dev/null 2>&1 | FileCheck %s
+
+@a = global i32 1, section "abc", !rename.key !0, !rename.key !1
+
+!0 = !{}
+!1 = !{}
+
+; CHECK: global value cannot have more then 1 rename metadata

llvm/test/Verifier/PowerPC/rename_operands.ll

@@ -0,0 +1,6 @@
+; RUN: not llvm-as %s -o /dev/null 2>&1 | FileCheck %s
+
+@a = global i32 1, section "abc", !rename.key !0
+
+!0 = !{!"Hello World!"}
+; CHECK:  rename metadata must have no operands