[RISCV] Remove R_RISCV_RVC_LUI Relocation (llvm#118714)

This was removed from the ABI in riscv-non-isa/riscv-elf-psabi-doc#398.
It is not emitted by LLVM, and seems to have been an internal
implementation detail in binutils.

This is a follow-up to 26ec5da which removed previous binutils
internal relocations when they were removed from the ABI.

The LLD implementation was not tested when it was added in
https://reviews.llvm.org/D39322

Author: lenary

lld/ELF/Arch/RISCV.cpp

@@ -267,7 +267,6 @@ RelExpr RISCV::getRelExpr(const RelType type, const Symbol &s,
   case R_RISCV_HI20:
   case R_RISCV_LO12_I:
   case R_RISCV_LO12_S:
-  case R_RISCV_RVC_LUI:
     return R_ABS;
   case R_RISCV_ADD8:
   case R_RISCV_ADD16:
@@ -373,19 +372,6 @@ void RISCV::relocate(uint8_t *loc, const Relocation &rel, uint64_t val) const {
     return;
   }
 
-  case R_RISCV_RVC_LUI: {
-    int64_t imm = SignExtend64(val + 0x800, bits) >> 12;
-    checkInt(ctx, loc, imm, 6, rel);
-    if (imm == 0) { // `c.lui rd, 0` is illegal, convert to `c.li rd, 0`
-      write16le(loc, (read16le(loc) & 0x0F83) | 0x4000);
-    } else {
-      uint16_t imm17 = extractBits(val + 0x800, 17, 17) << 12;
-      uint16_t imm16_12 = extractBits(val + 0x800, 16, 12) << 2;
-      write16le(loc, (read16le(loc) & 0xEF83) | imm17 | imm16_12);
-    }
-    return;
-  }
-
   case R_RISCV_JAL: {
     checkInt(ctx, loc, val, 21, rel);
     checkAlignment(ctx, loc, val, 2, rel);

lld/docs/ReleaseNotes.rst

@@ -39,6 +39,10 @@ ELF Improvements
 Breaking changes
 ----------------
 
+* Removed support for the (deprecated) `R_RISCV_RVC_LUI` relocation. This
+  was a binutils-internal relocation used during relaxation, and was not
+  emitted by compilers/assemblers.
+
 COFF Improvements
 -----------------
 * ``/includeglob`` has been implemented to match the behavior of ``--undefined-glob`` available for ELF.

llvm/include/llvm/BinaryFormat/ELFRelocs/RISCV.def

@@ -45,7 +45,6 @@ ELF_RELOC(R_RISCV_GOT32_PCREL,       41)
 ELF_RELOC(R_RISCV_ALIGN,             43)
 ELF_RELOC(R_RISCV_RVC_BRANCH,        44)
 ELF_RELOC(R_RISCV_RVC_JUMP,          45)
-ELF_RELOC(R_RISCV_RVC_LUI,           46)
 ELF_RELOC(R_RISCV_RELAX,             51)
 ELF_RELOC(R_RISCV_SUB6,              52)
 ELF_RELOC(R_RISCV_SET6,              53)