[AArch64] Use FirsRelocationKind+i fixup kinds to force relocations

For RELA targets, fixup kinds that force relocations (GOT, TLS, ALIGN,
RELAX, etc) can bypass `applyFixup` and be encoded as
`FirstRelocationKind+i`, as seen in LoongArch.

Author: MaskRay

llvm/include/llvm/MC/MCFixup.h

@@ -89,6 +89,10 @@ class MCFixup {
     FI.Loc = Loc;
     return FI;
   }
+  static MCFixup create(uint32_t Offset, const MCExpr *Value, unsigned Kind,
+                        SMLoc Loc = SMLoc()) {
+    return create(Offset, Value, MCFixupKind(Kind), Loc);
+  }
 
   MCFixupKind getKind() const { return Kind; }
 

llvm/lib/Target/AArch64/MCTargetDesc/AArch64AsmBackend.cpp

@@ -67,9 +67,9 @@ class AArch64AsmBackend : public MCAsmBackend {
         {"fixup_aarch64_pcrel_branch26", 0, 26, PCRelFlagVal},
         {"fixup_aarch64_pcrel_call26", 0, 26, PCRelFlagVal}};
 
-    // Fixup kinds from .reloc directive are like R_AARCH64_NONE. They do not
-    // require any extra processing.
-    if (Kind >= FirstLiteralRelocationKind)
+    // Fixup kinds from raw relocation types and .reloc directives force
+    // relocations and do not need these fields.
+    if (Kind >= FirstRelocationKind)
       return MCAsmBackend::getFixupKindInfo(FK_NONE);
 
     if (Kind < FirstTargetFixupKind)
@@ -442,7 +442,7 @@ void AArch64AsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
   if (!Value)
     return; // Doesn't change encoding.
   unsigned Kind = Fixup.getKind();
-  if (Kind >= FirstLiteralRelocationKind)
+  if (Kind >= FirstRelocationKind)
     return;
   unsigned NumBytes = getFixupKindNumBytes(Kind);
   MCFixupKindInfo Info = getFixupKindInfo(Fixup.getKind());

llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFObjectWriter.cpp

@@ -127,6 +127,11 @@ unsigned AArch64ELFObjectWriter::getRelocType(MCContext &Ctx,
     break;
   }
 
+  // Extract the relocation type from the fixup kind, after applying STT_TLS as
+  // needed.
+  if (Kind >= FirstRelocationKind)
+    return Kind - FirstRelocationKind;
+
   if (IsPCRel) {
     switch (Kind) {
     case FK_Data_1:

llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCCodeEmitter.cpp

@@ -749,9 +749,8 @@ void AArch64MCCodeEmitter::encodeInstruction(const MCInst &MI,
     auto Reloc = STI.getTargetTriple().getEnvironment() == Triple::GNUILP32
                      ? ELF::R_AARCH64_P32_TLSDESC_CALL
                      : ELF::R_AARCH64_TLSDESC_CALL;
-    Fixups.push_back(
-        MCFixup::create(0, MI.getOperand(0).getExpr(),
-                        MCFixupKind(FirstLiteralRelocationKind + Reloc)));
+    Fixups.push_back(MCFixup::create(0, MI.getOperand(0).getExpr(),
+                                     FirstRelocationKind + Reloc));
     return;
   }