<div dir="ltr"><div>i have a similar function in my code which uses four intermediates but compiles in reasonable time <br><br><span style="font-family:monospace,monospace"> {<br> // frustum<br> let f_width:Float = self.half_h * self.twice_size,<br> f_height:Float = self.half_k * self.twice_size,<br> dx:Float = -self.shift_x / self.half_h,<br> dy:Float = -self.shift_y / self.half_k<br><br> let clip_ratio:Float = 1000<br><br> self.projection_matrix =<br> [self.z/f_width , 0 , 0 , 0,<br> 0 , self.z/f_height, 0 , 0,<br> dx , dy , (1 + clip_ratio) / (1 - clip_ratio),-1,<br> 0 , 0 , self.z*2*clip_ratio / (1 - clip_ratio), 0]<br> }<br><br></span></div><span style="font-family:monospace,monospace">The intermediates are also things you’re going to want to store if anything for code clarity since the array literal starts looking messy when you shove long expressions into it. It also cuts down a little on the number of redundant operations you have to do (from 21 in your example to 16), especially divisions which you have six of in the original.<br></span></div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Jun 28, 2017 at 1:51 PM, Elia Cereda via swift-users <span dir="ltr"><<a href="mailto:swift-users@swift.org" target="_blank">swift-users@swift.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word"><div>Hi,</div><div><br></div><div>I currently writing a demo app to teach myself the fundamentals of Metal and a big part of that is obviously working with matrices. What I’m seeing is that the code build them has some serious compilation time problems.</div><div><br></div><div>The worst case is this function, which according to -debug-time-function-bodies takes over 9500ms of time to compile.</div><div><br></div><div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102)">static func frustum(l: Float, r: Float, t: Float, b: Float, n: Float, f: Float) -> float4x4 {</div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102)"> return float4x4(rows: [</div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102)"> [ 2 * n / (r - l), 0, (r + l) / (r - l), 0 ],</div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102)"> [ 0, 2 * n / (t - b), (t + b) / (t - b), 0 ],</div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102)"> [ 0, 0, -(f + n) / (f - n), -2 * f * n / (f - n) ],</div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102)"> [ 0, 0, -1, 1 ],</div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102)"> ])</div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102)">}</div></div><div><br></div><div>I’ve tried making some naive changes to the code and gotten it down to a much more reasonable 4ms, but the result is not something I would write if given a choice.</div><div><br></div><div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102)">static func frustum(l: Float, r: Float, t: Float, b: Float, n: Float, f: Float) -> float4x4 {</div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102)"> let twoN = 2 * n</div><p style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102);min-height:13px"> <br class="m_8653826296516026669webkit-block-placeholder"></p><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102)"> let rPlusL = r + l</div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102)"> let rMinusL = r - l</div><p style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102);min-height:13px"> <br class="m_8653826296516026669webkit-block-placeholder"></p><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102)"> let tPlusB = t + b</div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102)"> let tMinusB = t - b</div><p style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102);min-height:13px"> <br class="m_8653826296516026669webkit-block-placeholder"></p><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102)"> let fPlusN = f + n</div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102)"> let fMinusN = f - n</div><p style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102);min-height:13px"> <br class="m_8653826296516026669webkit-block-placeholder"></p><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102)"> return float4x4(rows: [</div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102)"> [ twoN / rMinusL, 0, rPlusL / rMinusL, 0 ],</div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102)"> [ 0, twoN / tMinusB, tPlusB / tMinusB, 0 ],</div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102)"> [ 0, 0, -fPlusN / fMinusN, -twoN * f / fMinusN ],</div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102)"> [ 0, 0, -1, 1 ],</div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102)"> ])</div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102)">}</div></div><div style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(102,102,102)"><br></div><div style="margin:0px;line-height:normal">I’m taking this to swift-users since I’m aware this is a known pain point with the compiler. Is this specific instance something that would be worth filing a bug for?</div><div style="margin:0px;line-height:normal"><br></div><div style="margin:0px;line-height:normal">Since I do not understand enough of the compiler to understand specifically what is causing problems with the first piece of code, I would also be extremely grateful if something from the core team (or anyone for that matter) could share some wisdom regarding what to do here.</div><div style="margin:0px;line-height:normal"><br></div><div style="margin:0px;line-height:normal">Specifically, is there something that could be done to the first code to reduce the amount of overloads that the compiler needs to consider? In my naive view of the world, a sum or a multiplication between two Floats can only ever produce another Float, is there some way to pass this knowledge to the compiler?</div><div><br></div>Regards,<br><div>
<div style="color:rgb(0,0,0);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">Elia Cereda</div>
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