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

[syzaara]

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.

[llvmbot]

@llvm/pr-subscribers-mc

Author: Zaara Syeda (syzaara)

Changes

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.

---

Full diff: https://github.com/llvm/llvm-project/pull/79530.diff

5 Files Affected:

• (modified) llvm/lib/MC/MCSectionXCOFF.cpp (+8-1)
• (modified) llvm/lib/MC/XCOFFObjectWriter.cpp (+8-2)
• (modified) llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp (+19-4)
• (modified) llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp (+2-5)
• (modified) llvm/test/CodeGen/PowerPC/basic-toc-data-local-linkage.ll (+6-4)

diff --git a/llvm/lib/MC/MCSectionXCOFF.cpp b/llvm/lib/MC/MCSectionXCOFF.cpp
index 02b1b972f339bf0..95d32e3580e3f55 100644
--- a/llvm/lib/MC/MCSectionXCOFF.cpp
+++ b/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);
 }
diff --git a/llvm/lib/MC/XCOFFObjectWriter.cpp b/llvm/lib/MC/XCOFFObjectWriter.cpp
index 343e2fc877bc3b1..11f8a72edeadafc 100644
--- a/llvm/lib/MC/XCOFFObjectWriter.cpp
+++ b/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;
diff --git a/llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp b/llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp
index 4f15ba497d84c45..1f4476d3907cdd3 100644
--- a/llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp
+++ b/llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp
@@ -2572,12 +2572,18 @@ 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;
   }
 
@@ -2738,8 +2744,17 @@ 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) {
diff --git a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp b/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
index b57d185bb638b8c..b86c9abeecf35f8 100644
--- a/llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp
+++ b/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;
 }
 
diff --git a/llvm/test/CodeGen/PowerPC/basic-toc-data-local-linkage.ll b/llvm/test/CodeGen/PowerPC/basic-toc-data-local-linkage.ll
index 0e131672b421e4b..4352852533ffb31 100644
--- a/llvm/test/CodeGen/PowerPC/basic-toc-data-local-linkage.ll
+++ b/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

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[diggerlin]

nit , use the check-prefix=CHECK as the same style as --check-prefix=OBJ32 in the following.

[diggerlin]

the most assemble are same. we do not need duplicate here. please fix all the following duplication.
the only different is
lwz 5, L..C1(2) # @a3 vs ld 5, L..C1(2) # @a3
lwz 4, L..C1(2) # @a3 vs ld 4, L..C1(2) # @a3

you can try

llc -mtriple powerpc-ibm-aix-xcoff -verify-machineinstrs < %s | FileCheck %s -DINSTR=lwz --check-prefix=CHECK

and

llc -mtriple powerpc64-ibm-aix-xcoff -verify-machineinstrs < %s | FileCheck %s -DINSTR=ld --check-prefix=CHECK

; CHECK: # %bb.0: # %entry
; CHECK-NEXT: la 4, a2TD
; CHECK-NEXT: la 5, a1TD
; CHECK-NEXT: stw 3, 0(4)
; CHECK-NEXT: [[INSTR]] 4, L..C0(2) # @a4
; CHECK-NEXT: stw 3, 0(5)
; CHECK-NEXT: [[INSTR]] 5, L..C1(2) # @A3
; CHECK-NEXT: stw 3, 0(4)
; CHECK-NEXT: stw 3, 0(5)
; CHECK-NEXT: blr

[diggerlin]

ditto

[diggerlin]

LGTM