<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">I agree with Reid and do not think we should change the ABI for Darwin.<div class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Dec 22, 2014, at 10:37 PM, Kuperstein, Michael M <<a href="mailto:michael.m.kuperstein@intel.com" class="">michael.m.kuperstein@intel.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="WordSection1" style="page: WordSection1; font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: 16.866666793823242px;" class=""><span style="color: rgb(31, 73, 125);" class="">Ping?<o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: 16.866666793823242px;" class=""><span style="color: rgb(31, 73, 125);" class=""> </span></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: 16.866666793823242px;" class=""><span style="color: rgb(31, 73, 125);" class="">Given that nobody objected so far, I’m considering changing it for all platforms, but I’d really like to get some feedback before I make an ABI-breaking change. ;-)<o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: 16.866666793823242px;" class=""><a name="_MailEndCompose" class=""><span style="color: rgb(31, 73, 125);" class=""> </span></a></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: 16.866666793823242px;" class=""><span style="color: rgb(31, 73, 125);" class="">Michael<o:p class=""></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: 16.866666793823242px;" class=""><span style="color: rgb(31, 73, 125);" class=""> </span></div><div class=""><div style="border-style: solid none none; border-top-color: rgb(181, 196, 223); border-top-width: 1pt; padding: 3pt 0cm 0cm;" class=""><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: normal;" class=""><b class=""><span style="font-size: 10pt; font-family: Tahoma, sans-serif;" class="">From:</span></b><span style="font-size: 10pt; font-family: Tahoma, sans-serif;" class=""><span class="Apple-converted-space"> </span><a href="mailto:llvmdev-bounces@cs.uiuc.edu" class="">llvmdev-bounces@cs.uiuc.edu</a> [<a href="mailto:llvmdev-bounces@cs.uiuc.edu" class="">mailto:llvmdev-bounces@cs.uiuc.edu</a>]<span class="Apple-converted-space"> </span><b class="">On Behalf Of<span class="Apple-converted-space"> </span></b>Kuperstein, Michael M<br class=""><b class="">Sent:</b><span class="Apple-converted-space"> </span>Monday, December 15, 2014 16:43<br class=""><b class="">To:</b><span class="Apple-converted-space"> </span><a href="mailto:LLVMdev@cs.uiuc.edu" class="">LLVMdev@cs.uiuc.edu</a><br class=""><b class="">Subject:</b><span class="Apple-converted-space"> </span>[LLVMdev] ABI incompatability when passing vector parameters on 32-bit x86<o:p class=""></o:p></span></div></div></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: 16.866666793823242px;" class=""><o:p class=""> </o:p></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: 16.866666793823242px;" class="">Hi all,<o:p class=""></o:p></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: 16.866666793823242px;" class=""><o:p class=""> </o:p></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: 16.866666793823242px;" class="">Recently, Reid Kleckner found an ABI incompatibility between clang and GCC in the way vector parameters are passed on 32-bit x86.<o:p class=""></o:p></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: 16.866666793823242px;" class="">(This is documented in PR21510.)<o:p class=""></o:p></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: 16.866666793823242px;" class=""><br class="">Specifically, GCC uses XMM0-XMM2 to pass the first 3 __m128 parameters, and the rest are passed on the stack. Clang passes an additional parameter by register, using XMM0-XMM3. The same applies to __m256 with YMM0-2 vs. YMM0-3. In theory, it would apply to __m512 as well, but currently clang doesn’t support passing __m512 in x86 mode at all. ICC has the same behavior as GCC, and it seems that MSVC in 32-bit mode only *allows* up to 3 vector parameters per function (when not using __vectorcall), and these 3 are passed in XMM0-XMM2, which is closer to the GCC behavior.<span class="Apple-converted-space"> </span><o:p class=""></o:p></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: 16.866666793823242px;" class=""><o:p class=""> </o:p></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: 16.866666793823242px;" class="">Unfortunately, it seems like there is no ABI specification to support either behavior as “correct”: while the x32 (“ILP32”) ABI explicitly specifies XMM0-XMM2, the latest version of the i386 psABI is too old to contain any useful information.<o:p class=""></o:p></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: 16.866666793823242px;" class="">Still, XMM0-XMM2 looks like the common choice, and I think the current clang behavior should be considered a bug.<o:p class=""></o:p></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: 16.866666793823242px;" class=""><o:p class=""> </o:p></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: 16.866666793823242px;" class="">The problem is that, regardless of whether it’s a bug or not, this behavior has been in place for many years, and changing it would mean breaking ABI compatibility with older clang versions.<o:p class=""></o:p></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: 16.866666793823242px;" class="">On the other hand, not changing it would mean continued ABI incompatibility with GCC.<o:p class=""></o:p></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: 16.866666793823242px;" class="">(This only applies to _m128 and _m256. Making the _m512 behavior GCC-compatible should be painless).<o:p class=""></o:p></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: 16.866666793823242px;" class=""><o:p class=""> </o:p></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: 16.866666793823242px;" class="">Reid (and I hope I’m not misrepresenting him here) suggested leaving the behavior as-is on platforms where clang is the system compiler (Darwin and BSD) and changing it elsewhere. However, I’m afraid interpreting the calling convention differently (compatible / incompatible with GCC) on different platforms may be confusing to end-uses.<o:p class=""></o:p></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: 16.866666793823242px;" class=""><o:p class=""> </o:p></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: 16.866666793823242px;" class="">Any thoughts on this, especially from OS/libraries people, will be very appreciated.<o:p class=""></o:p></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: 16.866666793823242px;" class=""><o:p class=""> </o:p></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: 16.866666793823242px;" class="">Thanks,<o:p class=""></o:p></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 11pt; font-family: Calibri, sans-serif; line-height: 16.866666793823242px;" class=""> Michael<span style="color: rgb(31, 73, 125);" class=""><o:p class=""></o:p></span></div></div><p style="margin-right: 0cm; margin-left: 0cm; font-size: 12pt; font-family: 'Times New Roman', serif; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">---------------------------------------------------------------------<br class="">Intel Israel (74) Limited</p><p style="margin-right: 0cm; margin-left: 0cm; font-size: 12pt; font-family: 'Times New Roman', serif; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">This e-mail and any attachments may contain confidential material for<br class="">the sole use of the intended recipient(s). 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