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Hash : 4e028ecd
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Date : 2023-02-02T08:55:37
SIMD/x86: Initialize simd_support before every use As long as a libjpeg instance is only used by one thread at a time, a program is technically within its rights to call jpeg_start_*compress() in one thread and jpeg_(read|write)_*(), with the same libjpeg instance, in a second thread. However, because the various jsimd_can*() functions are called within the body of jpeg_start_*compress() and simd_support is now thread-local (due to f579cc11b33e5bfeb9931e37cc74b4a33c95d2e6), that led to a situation in which simd_support was initialized in the first thread but not the second. The uninitialized value of simd_support is 0xFFFFFFFF, which the second thread interpreted to mean that it could use any instruction set, and when it attempted to use AVX2 instructions on a CPU that didn't support them, an illegal instruction error occurred. This issue was known to affect libvips. This commit modifies the i386 and x86-64 SIMD dispatchers so that the various jsimd_*() functions always call init_simd(), if simd_support is uninitialized, prior to dispatching based on the value of simd_support. Note that the other SIMD dispatchers don't need this, because only the x86 SIMD extensions currently support multiple instruction sets. This patch has been verified to be performance-neutral to within +/- 0.4% with 32-bit and 64-bit code running on a 2.8 GHz Intel Xeon W3530 and a 3.6 GHz Intel Xeon W2123. Fixes #649
