Correct alignment of atomic load and stores #19482
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vchuravy
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yuyichao
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Dec 2, 2016
| # Note for PPC: | ||
| # The OpenPower ABI for Linux Supplement -- 64-Bit ELF V2 ABI Specification | ||
| # defines that the alignments of types is sizeof(T). | ||
| if Sys.ARCH === :x86_64 || Sys.ARCH === :i686 || |
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The alignment here should not be what the ABI require, but what we can guarantee. See jl_gc_alignment for the correct definition.
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@yuyichao I decided to reuse the information from |
yuyichao
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Dec 2, 2016
| @@ -41,6 +41,13 @@ | |||
| extern "C" { | |||
| #endif | |||
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| // Make gc alignment available for threading | |||
| // see threads.jl alignment | |||
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We don't define functions before headers.
yuyichao
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Dec 2, 2016
This makes sure that atomic load and stores have the correct alignment as guaranteed by the gc.
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Squashed the pull-request. I will wait on travis and merge this tomorrow. |
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While updating LLVM from 3.7 to 3.9 on windows, I noticed that for 128bit atomics a libcall was issued,
instead of resolving to the hardware instruction (that we forcefully enable with the subtarget feature on X86
cx16).Disabling the
libatomicsupport injitlayers.cpprevealed the same regression on Linux.After discussion with @yuyichao (thank you again) we realized that the X86 ABI of atomic types requires an alignment of
sizeof(T)instead of the current
WORD_SIZE/8(see the libatomic ABI draft https://gcc.gnu.org/ml/gcc/2016-11/txt6ZlA_JS27i.txt).Load and stores should follow the alignment guarantees of the GC.
@tkelman this fixes the issue in #19472 properly and after merging this we will only need the SSP patch, from that PR.