Make HAVE_ATTRIBUTE_TARGET check also check that SSSE3 intrinsics work #1886
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GCC 4.8.5 and earlier accept SSSE3 intrinsics with -mssse3; these
compiler versions also accept __attribute__((target("ssse3"))) but
the attribute fails to enable compilation of the intrinsics.
Refactor the check to HAVE_ATTRIBUTE_TARGET_SSSE3, and check both
the attribute and that the SSSE3 intrinsics used (in simd.c) are
in fact compilable in a function with the attribute. Fixes samtools#1838.
jmarshall
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Feb 10, 2025
Apply PR samtools/htslib#1886. GCC 4.8.5 and earlier accept SSSE3 intrinsics with -mssse3; these compiler versions also accept __attribute__((target("ssse3"))) but the attribute fails to enable compilation of the intrinsics.
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Thanks, I've confirmed that this works with the ancient gcc on Centos 7. I'll also try to keep my centos 7 VM alive to check for any more regressions. |
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We released a new pysam based on HTSlib et al 1.21 last week, and now #1838 has been re-reported as pysam-developers/pysam#1327. So that nobody gets more support requests, it would be good to fix it so that the simd.c code is disabled for these ancient compilers.
Playing with the Compiler Explorer, I confirmed that GCC ≤ 4.8.5 cannot compile simd.c, while GCC ≥ 4.9.0 can. I considered
HTS_GCC_AT_LEAST(4,9)but realised that the existingHAVE_SSSE3appears to be exactly what is needed.However further Compiler Exploration showed that GCC ≤ 4.8.5 can compile these intrinsics with
-mssse3but not with merely__attribute__((target("ssse3"))), which fails to enable the intrinsics. Hence the right approach is to actually use some intrinsics in the configure test as @daviesrob suggested in #1838 (comment). This PR does that.