<html><head><meta http-equiv="Content-Type" content="text/html charset=windows-1252"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">On Sep 11, 2013, at 3:17 PM, Arnold Schwaighofer <<a href="mailto:aschwaighofer@apple.com">aschwaighofer@apple.com</a>> wrote:<br><div><br class="Apple-interchange-newline"><blockquote type="cite"><span style="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; float: none; display: inline !important;">However, this form cannot be matched to the shortest sequence of instructions on a platform where we have pairwise vector fadds (haddps - intel, VPADD - arm, faddp - aarch64) because we don’t have fast-math instruction flags at the selection dag level and therefore cannot reassociate the tree:</span><br style="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;"></blockquote></div><br><div>The general thrust of this work is great. I do want to point out that using HADDPS is a codesize win only for horizontal reductions; the fastest idiom is actually two shuffles + two adds (reciprocal throughput of 2 cycles vs. 4 for HADDPS). So we really do want to have a means to generate both of these, not only the pairwise ops.</div><div><br></div><div>– Steve</div></body></html>