[CHERIoT] Remove legacy handling of R_RISCV_CHERIOT_COMPARTMENT_LO_I without paired reloc.

This further simplifies control flow around CHERIoT relocation handling, and allows us to
collapse the CGPREL_LO_I and CGPREL_LO_S RelExpr's together.

Author: resistor

lld/ELF/Arch/RISCV.cpp

@@ -401,11 +401,10 @@ RelExpr RISCV::getRelExpr(const RelType type, const Symbol &s,
   case R_RISCV_CHERIOT_COMPARTMENT_HI:
     return isPCCRelative(ctx, loc, &s) ? R_PC : RE_CHERIOT_COMPARTMENT_CGPREL_HI;
   case R_RISCV_CHERIOT_COMPARTMENT_LO_I:
-    return RE_CHERIOT_COMPARTMENT_CGPREL_LO_I;
+  case R_RISCV_CHERIOT_COMPARTMENT_LO_S:
+    return RE_CHERIOT_COMPARTMENT_CGPREL_LO;
   case INTERNAL_R_RISCV_CHERIOT_COMPARTMENT_PCCREL_LO_I:
     return RE_RISCV_PC_INDIRECT;
-  case R_RISCV_CHERIOT_COMPARTMENT_LO_S:
-    return RE_CHERIOT_COMPARTMENT_CGPREL_LO_S;
   case R_RISCV_CHERIOT_COMPARTMENT_SIZE:
     return RE_CHERIOT_COMPARTMENT_SIZE;
   default:

lld/ELF/InputSection.cpp

@@ -1046,26 +1046,11 @@ uint64_t InputSectionBase::getRelocTargetVA(Ctx &ctx, const Relocation &r,
   case RE_MIPS_CHERI_CAPTAB_TPREL:
     assert(a == 0 && "capability table index relocs should not have addends");
     return ctx.in.mipsCheriCapTable->getTlsOffset(*r.sym);
-  // LO_I is used for both PCC and CGP-relative addresses.  For backwards
-  // compatibility, the symbol may be a CGP-relative symbol.  In newer code, it
-  // will always be the symbol containing the accompanying HI relocation.
-  case RE_CHERIOT_COMPARTMENT_CGPREL_LO_I: {
-    if (isPCCRelative(ctx, nullptr, r.sym)) {
-      if (const Relocation *hiRel = getRISCVPCRelHi20(ctx, this, r)) {
-        if (isPCCRelative(ctx, nullptr, hiRel->sym))
-          fatal("RE_CHERIOT_COMPARTMENT_CGPREL_LO_I relocation used for "
-                "PCC-relative access!");
-        return getBiasedCGPOffsetLo12(ctx, *hiRel->sym);
-      }
-      fatal("RE_CHERIOT_COMPARTMENT_CGPREL_LO_I relocation points to " +
-            r.sym->getName() +
-            " without an associated R_RISCV_PCREL_HI20 relocation");
-    }
-    return getBiasedCGPOffsetLo12(ctx, *r.sym);
-  }
   // Reached only for CGP-relative relocations.  PCC-relative addresses are
   // calculated with the R_PC and R_PC_INDIRECT cases.
-  case RE_CHERIOT_COMPARTMENT_CGPREL_LO_S:
+  case RE_CHERIOT_COMPARTMENT_CGPREL_LO:
+    if (isPCCRelative(ctx, nullptr, r.sym))
+      fatal("Malformed RE_CHERIOT_COMPARTMENT_CGPREL_LO_I relocation!");
     return getBiasedCGPOffsetLo12(ctx, *r.sym);
   case RE_CHERIOT_COMPARTMENT_CGPREL_HI:
     return (getBiasedCGPOffset(ctx, *r.sym) -

lld/ELF/Relocations.cpp

@@ -1073,8 +1073,7 @@ bool RelocationScanner::isStaticLinkTimeConstant(RelExpr e, RelType type,
           RE_MIPS_CHERI_CAPTAB_INDEX_CALL,
           RE_MIPS_CHERI_CAPTAB_INDEX_CALL_SMALL_IMMEDIATE,
           RE_MIPS_CHERI_CAPTAB_REL, RE_CHERIOT_COMPARTMENT_CGPREL_HI,
-          RE_CHERIOT_COMPARTMENT_CGPREL_LO_I, RE_CHERIOT_COMPARTMENT_CGPREL_LO_S,
-          RE_CHERIOT_COMPARTMENT_SIZE>(e))
+          RE_CHERIOT_COMPARTMENT_CGPREL_LO, RE_CHERIOT_COMPARTMENT_SIZE>(e))
     return true;
 
   // Cheri capability relocations are never static link time constants since

lld/ELF/Relocations.h

@@ -134,8 +134,7 @@ enum RelExpr {
   RE_MIPS_CHERI_CAPTAB_TLSLD,
   RE_MIPS_CHERI_CAPTAB_TPREL,
   RE_CHERIOT_COMPARTMENT_CGPREL_HI,
-  RE_CHERIOT_COMPARTMENT_CGPREL_LO_S,
-  RE_CHERIOT_COMPARTMENT_CGPREL_LO_I,
+  RE_CHERIOT_COMPARTMENT_CGPREL_LO,
   RE_CHERIOT_COMPARTMENT_SIZE,
   // Same as R_PC but with page-aligned semantics.
   RE_LOONGARCH_PAGE_PC,