[JITLink] Improve extractBits function

[StephenFan]

Summary

Address the advice proposed at patch D105429 . Use [Low, Low+size) to represent bits.

[StephenFan]

Change size_t to unsigned

[lhames]

LGTM.

llvm/lib/ExecutionEngine/JITLink/ELF_riscv.cpp

for (auto It = Bound.first; It != Bound.second; ++It) {
     if (It->getKind() == R_RISCV_PCREL_HI20)
       return *It;
   }
 
   return make_error<JITLinkError>(
       "No HI20 PCREL relocation type be found for LO12 PCREL relocation type");
 }
 
-static uint32_t extractBits(uint64_t Num, unsigned High, unsigned Low) {
-  return (Num & ((1ULL << (High + 1)) - 1)) >> Low;
+static uint32_t extractBits(uint32_t Num, unsigned Low, unsigned Size) {
+  return (Num & (((1ULL << (Size + 1)) - 1) << Low)) >> Low;
 }
 
 class ELFJITLinker_riscv : public JITLinker<ELFJITLinker_riscv> {
   friend class JITLinker<ELFJITLinker_riscv>;
 
 public:
   ELFJITLinker_riscv(std::unique_ptr<JITLinkContext> Ctx,
                      std::unique_ptr<LinkGraph> G, PassConfiguration PassConfig)
case R_RISCV_PCREL_LO12_I: {
           (RawInstr & 0xFFFFF) | (static_cast<uint32_t>(Lo & 0xFFF) << 20);
       break;
     }
     case R_RISCV_PCREL_LO12_S: {
       auto RelHI20 = getRISCVPCRelHi20(E);
       int64_t Value = RelHI20->getTarget().getAddress() +
                       RelHI20->getAddend() - E.getTarget().getAddress();
       int64_t Lo = Value & 0xFFF;
-      uint32_t Imm31_25 = extractBits(Lo, 11, 5) << 25;
-      uint32_t Imm11_7 = extractBits(Lo, 4, 0) << 7;
+      uint32_t Imm31_25 = extractBits(Lo, 5, 7) << 25;
+      uint32_t Imm11_7 = extractBits(Lo, 0, 5) << 7;
       uint32_t RawInstr = *(little32_t *)FixupPtr;
 
       *(little32_t *)FixupPtr = (RawInstr & 0x1FFF07F) | Imm31_25 | Imm11_7;
       break;
     }
     }
     return Error::success();
   }