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Update: VS2019 Update 2 is likely to do this; who do I need to prod such that I get to use these unconditionally in our <atomic> ?
<span id="🙂" title=":slight_smile:">🙂</span></div>
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<span title=":slight_smile:">Billy3</span></div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Billy O'Neal (VC LIBS)<br>
<b>Sent:</b> Tuesday, March 19, 2019 02:01 PM<br>
<b>To:</b> JF Bastien<br>
<b>Cc:</b> cfe-dev<br>
<b>Subject:</b> Re: [cfe-dev] FYI, Intel folks might be looking to add the __iso_volatile_Xxx family for MSVC STL <atomic> soon</font>
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<span style="color:rgb(0,0,0); font-family:Calibri,Arial,Helvetica,sans-serif; font-size:12pt">></span><span style="color:rgb(33,33,33); font-size:15px">MSVC’s volatiles on x86 were traditionally seq_cst when they could.</span><br>
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Normal loads are already seq_cst on x86 with no extra work. We still intend to use _InterlockedCompareExchange64 (on x86) or _InterlockedExchange64 (on amd64) to implement store. To be clear, this is in response to a specific customer bug where they want to
put an atomic<8 bytes> into read only memory, and want load() to not break their program with STATUS_ACCESS_VIOLATION. ( <a href="https://developercommunity.visualstudio.com/content/problem/274938/vs2017-1567158p2-stdatomicload-causes-write-access.html">https://developercommunity.visualstudio.com/content/problem/274938/vs2017-1567158p2-stdatomicload-causes-write-access.html</a>
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><span style="color:rgb(33,33,33); font-size:15px; background-color:rgb(255,255,255); display:inline!important">I think you should add type-generic versions as well.</span></div>
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I don't think C1XX or EDG have the ability to do that form of intrinsics right now, so to implement volatile_load/volatile_store we're going to need library tech that calls the __iso_volatile family.</div>
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><span style="color:rgb(33,33,33); font-size:15px; background-color:rgb(255,255,255); display:inline!important">who doesn’t love C++ library features that require compiler support? Right Billy?</span></div>
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<span style="font-family:Calibri,Arial,Helvetica,sans-serif; background-color:rgb(255,255,255); display:inline!important">I don't hate things that require compiler support. I hate things that require compiler support of the form nobody has demonstrated to be
reasonably implementable. Things that can be implemented in terms of traditional builtins or intrinsics (like volatile_load / volatile_store) are fine.</span><br>
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Billy3</div>
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<div id="x_divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> jfbastien@apple.com <jfbastien@apple.com> on behalf of JF Bastien <jfbastien@apple.com><br>
<b>Sent:</b> Tuesday, March 19, 2019 01:52 PM<br>
<b>To:</b> Billy O'Neal (VC LIBS)<br>
<b>Cc:</b> cfe-dev<br>
<b>Subject:</b> Re: [cfe-dev] FYI, Intel folks might be looking to add the __iso_volatile_Xxx family for MSVC STL <atomic> soon</font>
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<div class="">These? <a href="https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdocs.microsoft.com%2Fen-us%2Fcpp%2Fintrinsics%2Farm-intrinsics%3Fview%3Dvs-2017%23IsoVolatileLoadStore&data=02%7C01%7Cbion%40microsoft.com%7C9e4e63a643884977521e08d6acacc3e2%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636886255355080579&sdata=zfDNjIZrzKkc3RvHQSGdUadTzJytsmU5vmBbwyk%2FJW0%3D&reserved=0" originalsrc="https://docs.microsoft.com/en-us/cpp/intrinsics/arm-intrinsics?view=vs-2017#IsoVolatileLoadStore" shash="ZhaLVkNZwZOpIqT4j7SS/VDCBoBLjbcdxs2ZTGfYTpzJmls4KQZ+c6LIkec7AKs+wtYCqbRo8nl9DlvLma1doMrSqVWGsMzXB1lnhbu+DAYE2rEzGhuN3YZbWMUUGosuSXqfrUJGqIF4MSOuQmf76PElSaYhpQcnKfEDi5l/Miw=" class="">https://docs.microsoft.com/en-us/cpp/intrinsics/arm-intrinsics?view=vs-2017#IsoVolatileLoadStore</a></div>
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<div class=""><font face="Courier" class="">__int16 __iso_volatile_load16(const volatile __int16 * Location)</font></div>
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<div class=""><font face="Courier" class="">__int32 __iso_volatile_load32(const volatile __int32 * Location)</font></div>
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<div class=""><font face="Courier" class="">__int64 __iso_volatile_load64(const volatile __int64 * Location)</font></div>
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<div class=""><font face="Courier" class="">__int8 __iso_volatile_load8(const volatile __int8 * Location)</font></div>
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<div class=""><font face="Courier" class="">void __iso_volatile_store16(volatile __int16 * Location, __int16 Value)</font></div>
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<div class=""><font face="Courier" class="">void __iso_volatile_store32(volatile __int32 * Location, __int32 Value)</font></div>
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<div class=""><font face="Courier" class="">void __iso_volatile_store64(volatile __int64 * Location, __int64 Value)</font></div>
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<div class=""><font face="Courier" class="">void __iso_volatile_store8(volatile __int8 * Location, __int8 Value)</font></div>
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<div class="">Seems fine, given how MSVC’s volatiles on x86 were traditionally seq_cst when they could. I think the above match the LLVM IR semantics precisely.</div>
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<div class="">I think you should add type-generic versions as well. Then you’ve got a nice builtin for <a href="https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwg21.link%2FP1382&data=02%7C01%7Cbion%40microsoft.com%7C9e4e63a643884977521e08d6acacc3e2%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636886255355080579&sdata=H8iAKCg12tAuAqfupoU0MMPFYGrMxDc%2F3QxkPkbdRDE%3D&reserved=0" originalsrc="http://wg21.link/P1382" shash="h4NFTdR6B59jFZ89nMq27orCtUZ5SzS6KgzVPmGFWDyJZX6aRwkSAjk3L1Maisqstlv+K403TV01fHi98K7TWhYOi7Lelq/fjFVbMPpWgNI6PS1NaH6+21ZPzajM9oCfpsLqd5hO9dfo37FXgVLW83RmxqQ0SKDnJaDzOiLvwPQ=" class="">volatile_load<T>
/ volatile_store<T></a>, and who doesn’t love C++ library features that require compiler support? Right Billy? 😁</div>
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<div class="">On Mar 19, 2019, at 1:32 PM, Billy O'Neal (VC LIBS) via cfe-dev <<a href="mailto:cfe-dev@lists.llvm.org" class="">cfe-dev@lists.llvm.org</a>> wrote:</div>
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I think Clang has those already implemented for ARM (since our <atomic> compiles there) but we are looking to use them instead of cmpxchg8b to implement load of atomic<8 bytes> on x86 soon.</div>
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Billy3</div>
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<a href="mailto:cfe-dev@lists.llvm.org" class="" style="font-family:Helvetica; font-size:12px; font-style:normal; font-variant-caps:normal; font-weight:normal; letter-spacing:normal; orphans:auto; text-align:start; text-indent:0px; text-transform:none; white-space:normal; widows:auto; word-spacing:0px">cfe-dev@lists.llvm.org</a><br class="" style="font-family:Helvetica; font-size:12px; font-style:normal; font-variant-caps:normal; font-weight:normal; letter-spacing:normal; text-align:start; text-indent:0px; text-transform:none; white-space:normal; word-spacing:0px; text-decoration:none">
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