[XCOFF] Enable available_externally linkage for functions.

Summary: D80642 added support for emitting AvailableExternally Linkage on AIX. However, an assertion of "Trying to get csect representation of this symbol but none was set." occurred when a function is declared as available_externally. This is due to we missing to generate a csect for the function. This patch fixes it.

Reviewed By: hubert.reinterpretcast, shchenz

Differential Revision: https://reviews.llvm.org/D156213

Signed-off-by: Esme Yi <esme.yi@ibm.com>
(cherry picked from commit e83b8a5)

llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp

@@ -2628,12 +2628,12 @@ MCSymbol *TargetLoweringObjectFileXCOFF::getFunctionEntryPointSymbol(
   // function entry point csect instead. And for function delcarations, the
   // undefined symbols gets treated as csect with XTY_ER property.
   if (((TM.getFunctionSections() && !Func->hasSection()) ||
-       Func->isDeclaration()) &&
+       Func->isDeclarationForLinker()) &&
       isa<Function>(Func)) {
     return getContext()
         .getXCOFFSection(
             NameStr, SectionKind::getText(),
-            XCOFF::CsectProperties(XCOFF::XMC_PR, Func->isDeclaration()
+            XCOFF::CsectProperties(XCOFF::XMC_PR, Func->isDeclarationForLinker()
                                                       ? XCOFF::XTY_ER
                                                       : XCOFF::XTY_SD))
         ->getQualNameSymbol();

llvm/test/CodeGen/PowerPC/aix-available-externally-linkage-fun.ll

@@ -0,0 +1,51 @@
+; RUN: llc -verify-machineinstrs -mtriple powerpc-ibm-aix-xcoff -mcpu=pwr4 \
+; RUN:     -mattr=-altivec < %s | FileCheck %s
+
+; RUN: llc -verify-machineinstrs -mtriple powerpc64-ibm-aix-xcoff -mcpu=pwr4 \
+; RUN:     -mattr=-altivec < %s | FileCheck %s
+
+; RUN: llc -verify-machineinstrs -mtriple powerpc-ibm-aix-xcoff -mcpu=pwr4 \
+; RUN:     -mattr=-altivec -filetype=obj -o %t.o < %s
+; RUN: llvm-readobj --symbols %t.o | FileCheck --check-prefix=OBJ %s
+
+; RUN: llc -verify-machineinstrs -mtriple powerpc64-ibm-aix-xcoff -mcpu=pwr4 \
+; RUN:     -mattr=-altivec -filetype=obj -o %t64.o < %s
+; RUN: llvm-readobj --symbols %t64.o | FileCheck --check-prefix=OBJ %s
+
+define available_externally i32 @foo(i32 %a) {
+entry:
+  ret i32 %a
+}
+
+; CHECK: .extern .foo[PR]
+; CHECK: .extern foo[DS]
+
+; OBJ:      Name: .foo
+; OBJ-NEXT: Value (RelocatableAddress): 0x0
+; OBJ-NEXT: Section: N_UNDEF
+; OBJ-NEXT: Type: 0x0
+; OBJ-NEXT: StorageClass: C_EXT (0x2)
+; OBJ-NEXT: NumberOfAuxEntries: 1
+; OBJ-NEXT: CSECT Auxiliary Entry {
+; OBJ-NEXT:   Index: 2
+; OBJ-NEXT:   SectionLen: 0
+; OBJ-NEXT:   ParameterHashIndex: 0x0
+; OBJ-NEXT:   TypeChkSectNum: 0x0
+; OBJ-NEXT:   SymbolAlignmentLog2: 0
+; OBJ-NEXT:   SymbolType: XTY_ER (0x0)
+; OBJ-NEXT:   StorageMappingClass: XMC_PR (0x0)
+
+; OBJ:      Name: foo
+; OBJ-NEXT: Value (RelocatableAddress): 0x0
+; OBJ-NEXT: Section: N_UNDEF
+; OBJ-NEXT: Type: 0x0
+; OBJ-NEXT: StorageClass: C_EXT (0x2)
+; OBJ-NEXT: NumberOfAuxEntries: 1
+; OBJ-NEXT: CSECT Auxiliary Entry {
+; OBJ-NEXT:   Index: 4
+; OBJ-NEXT:   SectionLen: 0
+; OBJ-NEXT:   ParameterHashIndex: 0x0
+; OBJ-NEXT:   TypeChkSectNum: 0x0
+; OBJ-NEXT:   SymbolAlignmentLog2: 0
+; OBJ-NEXT:   SymbolType: XTY_ER (0x0)
+; OBJ-NEXT:   StorageMappingClass: XMC_DS (0xA)