kc3-lang/libjpeg-turbo

2016-07-13T12:15:02

Fix AArch64 ABI conformance issue in SIMD code In the AArch64 ABI, the high (unused) DWORD of a 32-bit argument's register is undefined, so it was incorrect to use 64-bit instructions to transfer a JDIMENSION argument in the 64-bit NEON SIMD functions. The code worked thus far only because the existing compiler optimizers weren't smart enough to do anything else with the register in question, so the upper 32 bits happened to be all zeroes. The latest builds of Clang/LLVM have a smarter optimizer, and under certain circumstances, it will attempt to load-combine adjacent 32-bit integers from one of the libjpeg structures into a single 64-bit integer and pass that 64-bit integer as a 32-bit argument to one of the SIMD functions (which is allowed by the ABI, since the upper 32 bits of the 32-bit argument's register are undefined.) This caused the libjpeg-turbo regression tests to crash. This patch tries to use the Wn registers whenever possible. Otherwise, it uses a zero-extend instruction to avoid using the upper 32 bits of the 64-bit registers, which are not guaranteed to be valid for 32-bit arguments. Based on https://github.com/sebpop/libjpeg-turbo/commit/1fbae13021eb98f6fffdfaf8678fcdb00b0b04d9 Closes #91. Refer also to android-ndk/ndk#110 and https://llvm.org/bugs/show_bug.cgi?id=28393