[Coverity] Non-local variable isn't restored

[AlexeySachkov]

The issue was discovered by Coverity scan that we do at intel/llvm repo, you can view the scan and request access here: https://scan.coverity.com/projects/intel-llvm?tab=overview

CID 546125:

SPIRV-LLVM-Translator/lib/SPIRV/SPIRVReader.cpp

Lines 5696 to 5705 in 35827fe

	if (!BM->getFnVarSpvOut().empty()) {
	auto SaveOpt = SPIRVUseTextFormat;
	auto OFSSpv = std::ofstream(BM->getFnVarSpvOut(), std::ios::binary);
	SPIRVUseTextFormat = false;
	OFSSpv << *BM;
	if (BM->getError(ErrMsg) != SPIRVEC_Success) {
	return false;
	}
	SPIRVUseTextFormat = SaveOpt;
	}

SPIRVUseTextFormat value is not restored to its original value in case of errors.

Whilst I don't know if there is a practical use case for this, this is technically a problem, because readSpirv is part of the public translator API:

SPIRV-LLVM-Translator/include/LLVMSPIRVLib.h

Lines 160 to 163 in 35827fe

	/// \brief Load SPIR-V from istream and translate to LLVM module.
	/// \returns true if succeeds.
	bool readSpirv(LLVMContext &C, const SPIRV::TranslatorOpts &Opts,
	std::istream &IS, Module *&M, std::string &ErrMsg);

As such, there could exist an application which calls it multiple times where some invocations may produce unexpected results