MCFixup: Remove FK_PCRel_

The generic FK_Data_ fixup kinds handle both absolute and PC-relative
fixups. ELFObjectWriter sets IsPCRel to true for `.long foo-.`, so the
backend has to handle PC-relative FK_Data_.

However, the existence of FK_PCRel_ encouraged backends to implement it
as a separate fixup type, leading to redundant and error-prone code.

Removing FK_PCRel_ simplifies the overall fixup mechanism.

Author: MaskRay

llvm/include/llvm/MC/MCFixup.h

@@ -34,10 +34,6 @@ enum MCFixupKind : uint16_t {
   FK_Data_4,      ///< A four-byte fixup.
   FK_Data_8,      ///< A eight-byte fixup.
   FK_Data_leb128, ///< A leb128 fixup.
-  FK_PCRel_1,     ///< A one-byte pc relative fixup.
-  FK_PCRel_2,     ///< A two-byte pc relative fixup.
-  FK_PCRel_4,     ///< A four-byte pc relative fixup.
-  FK_PCRel_8,     ///< A eight-byte pc relative fixup.
   FK_SecRel_1,    ///< A one-byte section relative fixup.
   FK_SecRel_2,    ///< A two-byte section relative fixup.
   FK_SecRel_4,    ///< A four-byte section relative fixup.

llvm/lib/MC/MCAsmBackend.cpp

@@ -95,10 +95,6 @@ MCFixupKindInfo MCAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
       {"FK_Data_4", 0, 32, 0},
       {"FK_Data_8", 0, 64, 0},
       {"FK_Data_leb128", 0, 0, 0},
-      {"FK_PCRel_1", 0, 8, 0},
-      {"FK_PCRel_2", 0, 16, 0},
-      {"FK_PCRel_4", 0, 32, 0},
-      {"FK_PCRel_8", 0, 64, 0},
       {"FK_SecRel_1", 0, 8, 0},
       {"FK_SecRel_2", 0, 16, 0},
       {"FK_SecRel_4", 0, 32, 0},

llvm/lib/Target/Hexagon/MCTargetDesc/HexagonAsmBackend.cpp

@@ -317,7 +317,6 @@ class HexagonAsmBackend : public MCAsmBackend {
       case FK_Data_1:
       case FK_Data_2:
       case FK_Data_4:
-      case FK_PCRel_4:
       case fixup_Hexagon_32:
         // Leave these relocations alone as they are used for EH.
         return false;
@@ -335,8 +334,7 @@ class HexagonAsmBackend : public MCAsmBackend {
         return 1;
       case FK_Data_2:
         return 2;
-      case FK_Data_4:         // this later gets mapped to R_HEX_32
-      case FK_PCRel_4:        // this later gets mapped to R_HEX_32_PCREL
+      case FK_Data_4: // this later gets mapped to R_HEX_32 or R_HEX_32_PCREL
       case fixup_Hexagon_32:
       case fixup_Hexagon_B32_PCREL_X:
       case fixup_Hexagon_B22_PCREL: