Move X86-specific MCSymbolRefExpr::VariantKind to X86MCExpr::Specifier

Move target-specific members outside of MCSymbolRefExpr::VariantKind
(a legacy interface I am eliminating). Most changes are mechanic,
except:

* ELFObjectWriter::shouldRelocateWithSymbol
* The legacy generic code uses `ELFObjectWriter::fixSymbolsInTLSFixups`
  to set `STT_TLS` (and use an unnecessary expression walk). The better
  way is to do this in `getRelocType`, which I have done for
  AArch64, PowerPC, and RISC-V.

In the future, we should encode expressions with a relocation specifier
as X86MCExpr and use MCValue::RefKind to hold the specifier of the
relocatable expression.
https://maskray.me/blog/2025-03-16-relocation-generation-in-assemblers

While here, rename "Modifier' to "Specifier":

> "Relocation modifier", though concise, suggests adjustments happen during the linker's relocation step rather than the assembler's expression evaluation. I landed on "relocation specifier" as the winner. It's clear, aligns with Arm and IBM’s usage, and fits the assembler's role seamlessly.

Pull Request: llvm#132149

Author: MaskRay

llvm/include/llvm/MC/MCExpr.h

@@ -199,14 +199,10 @@ class MCSymbolRefExpr : public MCExpr {
     VK_GOT,
     VK_GOTENT,
     VK_GOTOFF,
-    VK_GOTREL,
-    VK_PCREL,
     VK_GOTPCREL,
-    VK_GOTPCREL_NORELAX,
     VK_GOTTPOFF,
     VK_INDNTPOFF,
     VK_NTPOFF,
-    VK_GOTNTPOFF,
     VK_PLT,
     VK_TLSGD,
     VK_TLSLD,
@@ -223,7 +219,6 @@ class MCSymbolRefExpr : public MCExpr {
     VK_GOTPAGE,
     VK_GOTPAGEOFF,
     VK_SECREL,
-    VK_SIZE,    // symbol@SIZE
     VK_WEAKREF, // The link between the symbols in .weakref foo, bar
     VK_FUNCDESC,
     VK_GOTFUNCDESC,
@@ -232,9 +227,6 @@ class MCSymbolRefExpr : public MCExpr {
     VK_TLSLDM_FDPIC,
     VK_GOTTPOFF_FDPIC,
 
-    VK_X86_ABS8,
-    VK_X86_PLTOFF,
-
     VK_ARM_NONE,
     VK_ARM_GOT_PREL,
     VK_ARM_TARGET1,
@@ -261,8 +253,7 @@ class MCSymbolRefExpr : public MCExpr {
     VK_AMDGPU_ABS32_LO,      // symbol@abs32@lo
     VK_AMDGPU_ABS32_HI,      // symbol@abs32@hi
 
-    VK_TPREL,
-    VK_DTPREL
+    FirstTargetSpecifier,
   };
 
 private:

llvm/lib/MC/ELFObjectWriter.cpp

@@ -1269,7 +1269,6 @@ bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
   case MCSymbolRefExpr::VK_GOT:
   case MCSymbolRefExpr::VK_PLT:
   case MCSymbolRefExpr::VK_GOTPCREL:
-  case MCSymbolRefExpr::VK_GOTPCREL_NORELAX:
     return true;
   }
 
@@ -1526,16 +1525,13 @@ void ELFObjectWriter::fixSymbolsInTLSFixups(MCAssembler &Asm,
     case MCSymbolRefExpr::VK_GOTTPOFF:
     case MCSymbolRefExpr::VK_INDNTPOFF:
     case MCSymbolRefExpr::VK_NTPOFF:
-    case MCSymbolRefExpr::VK_GOTNTPOFF:
     case MCSymbolRefExpr::VK_TLSCALL:
     case MCSymbolRefExpr::VK_TLSDESC:
     case MCSymbolRefExpr::VK_TLSGD:
     case MCSymbolRefExpr::VK_TLSLD:
     case MCSymbolRefExpr::VK_TLSLDM:
     case MCSymbolRefExpr::VK_TPOFF:
-    case MCSymbolRefExpr::VK_TPREL:
     case MCSymbolRefExpr::VK_DTPOFF:
-    case MCSymbolRefExpr::VK_DTPREL:
       break;
     }
     Asm.registerSymbol(symRef.getSymbol());

llvm/lib/Target/X86/AsmParser/X86AsmParser.cpp

@@ -2116,7 +2116,7 @@ bool X86AsmParser::ParseIntelExpression(IntelExprStateMachine &SM, SMLoc &End) {
         if (IDVal == "f" || IDVal == "b") {
           MCSymbol *Sym =
               getContext().getDirectionalLocalSymbol(IntVal, IDVal == "b");
-          MCSymbolRefExpr::VariantKind Variant = MCSymbolRefExpr::VK_None;
+          auto Variant = X86MCExpr::VK_None;
           const MCExpr *Val =
               MCSymbolRefExpr::create(Sym, Variant, getContext());
           if (IDVal == "b" && Sym->isUndefined())
@@ -2263,7 +2263,7 @@ bool X86AsmParser::ParseIntelInlineAsmIdentifier(
     return false;
   // Create the symbol reference.
   MCSymbol *Sym = getContext().getOrCreateSymbol(Identifier);
-  MCSymbolRefExpr::VariantKind Variant = MCSymbolRefExpr::VK_None;
+  auto Variant = X86MCExpr::VK_None;
   Val = MCSymbolRefExpr::create(Sym, Variant, getParser().getContext());
   return false;
 }

llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp

@@ -9,6 +9,7 @@
 #include "MCTargetDesc/X86BaseInfo.h"
 #include "MCTargetDesc/X86EncodingOptimization.h"
 #include "MCTargetDesc/X86FixupKinds.h"
+#include "MCTargetDesc/X86MCExpr.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/BinaryFormat/ELF.h"
 #include "llvm/BinaryFormat/MachO.h"
@@ -360,7 +361,7 @@ static bool hasVariantSymbol(const MCInst &MI) {
       continue;
     const MCExpr &Expr = *Operand.getExpr();
     if (Expr.getKind() == MCExpr::SymbolRef &&
-        cast<MCSymbolRefExpr>(Expr).getKind() != MCSymbolRefExpr::VK_None)
+        getSpecifier(cast<MCSymbolRefExpr>(&Expr)) != X86MCExpr::VK_None)
       return true;
   }
   return false;
@@ -746,7 +747,7 @@ bool X86AsmBackend::fixupNeedsRelaxationAdvanced(const MCAssembler &Asm,
     MCValue Target;
     if (Fixup.getValue()->evaluateAsRelocatable(Target, &Asm) &&
         Target.getSymA() &&
-        Target.getSymA()->getKind() == MCSymbolRefExpr::VK_X86_ABS8)
+        getSpecifier(Target.getSymA()) == X86MCExpr::VK_ABS8)
       return false;
   }
   return true;