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da48edfc49
Because ofbf01ed2fbc, the simd field in huff_entropy_encoder (and, by extension, the simd field in savable_state) is only initialized if WITH_SIMD is defined. Due to an oversight, the simd field in savable_state was queried in flush_bits() regardless of whether WITH_SIMD was defined. In most cases, both branches of the query have identical code, and the optimizer removes the branch. However, because the legacy Neon GAS Huffman encoder uses the older bit buffer logic from libjpeg-turbo 2.0.x and prior (refer to087c29e07f), the branches do not have identical code when building for AArch64 with NEON_INTRINSICS undefined (which will be the case if WITH_SIMD is undefined.) Thus, if libjpeg-turbo was built for AArch64 with the SIMD extensions disabled at build time, it was possible for the Neon GAS branch in flush_bits() to be taken, which would have set put_bits to a value that is incorrect for the C Huffman encoder. Referring to #728, a user reported that this issue sometimes caused libjpeg-turbo to generate bogus JPEG images if it was built for AArch64 without SIMD extensions and subsequently used through the Qt framework. (It should be noted, however, that disabling the SIMD extensions in AArch64 builds of libjpeg-turbo is inadvisable for performance reasons.) I was unable to reproduce the issue on Linux/AArch64 using libjpeg-turbo alone, despite testing various versions of GCC and Clang and various optimization levels. However, the issue is reproducible using MSan with -O0, so this commit also modifies the GitHub Actions workflow so that compiler optimization is disabled in the linux-msan job. That should prevent the issue or similar issues from re-emerging. Fixes #728