[AIX] [XCOFF] Add support for common and local common symbols in the TOC

This patch adds support for common and local symbols in the TOC for AIX.
Note that we need to update isVirtualSection so as a common symbol in TOC will
have the symbol type XTY_CM and will be initialized when placed in the TOC so
sections with this type are no longer virtual.

Author: Zaara Syeda

llvm/lib/MC/MCSectionXCOFF.cpp

@@ -82,6 +82,11 @@ void MCSectionXCOFF::printSwitchToSection(const MCAsmInfo &MAI, const Triple &T,
   }
 
   if (isCsect() && getMappingClass() == XCOFF::XMC_TD) {
+    // Common csect type (uninitialized storage) does not have to print csect
+    // directive for section switching unless it is local.
+    if (getKind().isCommon() && !getKind().isBSSLocal())
+      return;
+
     assert((getKind().isBSSExtern() || getKind().isBSSLocal()) &&
            "Unexepected section kind for toc-data");
     printCsectDirective(OS);
@@ -135,5 +140,7 @@ bool MCSectionXCOFF::isVirtualSection() const {
     return false;
   assert(isCsect() &&
          "Handling for isVirtualSection not implemented for this section!");
-  return XCOFF::XTY_CM == CsectProp->Type;
+  // XTY_CM sections are virtual except for toc-data symbols.
+  return (XCOFF::XTY_CM == CsectProp->Type) &&
+         (getMappingClass() != XCOFF::XMC_TD);
 }

llvm/lib/MC/XCOFFObjectWriter.cpp

@@ -533,9 +533,15 @@ CsectGroup &XCOFFObjectWriter::getCsectGroup(const MCSectionXCOFF *MCSec) {
     return TOCCsects;
   case XCOFF::XMC_TC:
   case XCOFF::XMC_TE:
-  case XCOFF::XMC_TD:
     assert(XCOFF::XTY_SD == MCSec->getCSectType() &&
-           "Only an initialized csect can contain TC entry.");
+           "A TOC symbol must be an initialized csect.");
+    assert(!TOCCsects.empty() &&
+           "We should at least have a TOC-base in this CsectGroup.");
+    return TOCCsects;
+  case XCOFF::XMC_TD:
+    assert((XCOFF::XTY_SD == MCSec->getCSectType() ||
+            XCOFF::XTY_CM == MCSec->getCSectType()) &&
+           "Symbol type incompatible with toc-data.");
     assert(!TOCCsects.empty() &&
            "We should at least have a TOC-base in this CsectGroup.");
     return TOCCsects;

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

@@ -2571,12 +2571,18 @@ void PPCAIXAsmPrinter::emitGlobalVariableHelper(const GlobalVariable *GV) {
     GVSym->setStorageClass(
         TargetLoweringObjectFileXCOFF::getStorageClassForGlobal(GV));
 
-    if (GVKind.isBSSLocal() || GVKind.isThreadBSSLocal())
+    if (GVKind.isBSSLocal() && Csect->getMappingClass() == XCOFF::XMC_TD) {
+      OutStreamer->emitZeros(Size);
+    } else if (GVKind.isBSSLocal() || GVKind.isThreadBSSLocal()) {
+      assert(Csect->getMappingClass() != XCOFF::XMC_TD &&
+             "BSS local toc-data already handled and TLS variables "
+             "incompatible with XMC_TD");
       OutStreamer->emitXCOFFLocalCommonSymbol(
           OutContext.getOrCreateSymbol(GVSym->getSymbolTableName()), Size,
           GVSym, Alignment);
-    else
+    } else {
       OutStreamer->emitCommonSymbol(GVSym, Size, Alignment);
+    }
     return;
   }
 
@@ -2737,8 +2743,17 @@ void PPCAIXAsmPrinter::emitEndOfAsmFile(Module &M) {
     TS->emitTCEntry(*I.first.first, I.first.second);
   }
 
-  for (const auto *GV : TOCDataGlobalVars)
-    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);
+  }
 }
 
 bool PPCAIXAsmPrinter::doInitialization(Module &M) {

llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp

@@ -551,13 +551,10 @@ static bool hasTocDataAttr(SDValue Val, unsigned PointerSize) {
          "A GlobalVariable with size larger than a TOC entry is not currently "
          "supported by the toc data transformation.");
 
-  if (GV->hasLocalLinkage() || GV->hasPrivateLinkage())
-    report_fatal_error("A GlobalVariable with private or local linkage is not "
+  if (GV->hasPrivateLinkage())
+    report_fatal_error("A GlobalVariable with private linkage is not "
                        "currently supported by the toc data transformation.");
 
-  assert(!GV->hasCommonLinkage() &&
-         "Tentative definitions cannot have the mapping class XMC_TD.");
-
   return true;
 }
 

llvm/test/CodeGen/PowerPC/basic-toc-data-local-linkage.ll

@@ -1,6 +1,6 @@
-; RUN: not --crash llc  -mtriple powerpc-ibm-aix-xcoff  -verify-machineinstrs \
+; RUN: llc  -mtriple powerpc-ibm-aix-xcoff  -verify-machineinstrs \
 ; RUN:     < %s 2>&1 | FileCheck %s
-; RUN: not --crash llc  -mtriple powerpc64-ibm-aix-xcoff  -verify-machineinstrs \
+; RUN: llc  -mtriple powerpc64-ibm-aix-xcoff  -verify-machineinstrs \
 ; RUN:     < %s 2>&1 | FileCheck %s
 
 @ilocal = internal global i32 0, align 4 #0
@@ -11,6 +11,8 @@ define dso_local i32 @read_i32_local_linkage() {
     ret i32 %0
 }
 
-; CHECK: LLVM ERROR: A GlobalVariable with private or local linkage is not currently supported by the toc data transformation.
-
 attributes #0 = { "toc-data" }
+
+; CHECK:      .toc
+; CHECK-NEXT: .csect ilocal[TD],2
+; CHECK-NEXT: .space  4