[llvm] [RISCV] Support .option {no}exact (PR #122483)

[Sam Elliott via llvm-commits]

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@@ -344,6 +344,10 @@ std::pair<bool, bool> RISCVAsmBackend::relaxLEB128(const MCAssembler &Asm,
 // Given a compressed control flow instruction this function returns
 // the expanded instruction.
 unsigned RISCVAsmBackend::getRelaxedOpcode(unsigned Op) const {
+  // Disable relaxation if FeatureExactAssembly
+  if (STI.hasFeature(RISCV::FeatureExactAssembly))
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lenary wrote:

Yeah, this is indeed a different STI to `mayNeedRelaxation`.

I wasn't sure about changing `relaxInstruction`, because of the `llvm_unreachable` which suggested to me it would never be called if `mayNeedRelaxation` returned false, and I also wasn't sure what would happen if we never updated `Inst`. I can certainly try that approach, I agree the current check is not actually very good.

https://github.com/llvm/llvm-project/pull/122483