<html><head><meta http-equiv="Content-Type" content="text/html charset=iso-8859-1"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div><br></div>We currently do not analyze the source code to check the usage of the low bits.<div><br><div>In the backend, the alignment is already clamped to the correct value, so the backend optimizations will not treat those low bits as zero.</div><div><br></div><div>-Manman</div><div><br></div><div><div><div>On Feb 4, 2013, at 6:08 PM, Eric Christopher <<a href="mailto:echristo@gmail.com">echristo@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div dir="ltr">Also I could be missing it but I couldn't spot the code that checks for the usage of the bits in not aligning/warning/erroring? Quick pointer?<div><br></div><div style="">Thanks!</div><div><br></div><div style="">
-eric</div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Mon, Feb 4, 2013 at 5:41 PM, Eric Christopher <span dir="ltr"><<a href="mailto:echristo@gmail.com" target="_blank">echristo@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><br><div class="gmail_extra"><br><br><div class="gmail_quote"><div class="im">On Mon, Feb 4, 2013 at 5:35 PM, Manman Ren <span dir="ltr"><<a href="mailto:mren@apple.com" target="_blank">mren@apple.com</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><br></div>Yes, there are related discussions in r169197 and "[PATCH] Stack Alignment: clamp the alignment of stack objects in MachineFrameInfo".<div>
<br></div><div>But people can use a 32-byte alignment attribute on a machine which only supports 16-byte stack alignment.</div><div>If the source code further assumes the low bits are zeros, they will get wrong result.</div>
<div>But if not, a hard error is too much and it will make existing code which can compile with earlier version failed to build with this patch.</div></div></blockquote><div><br></div></div><div>And to use the other side of the argument that won last time :)</div>
<div><br></div><div>But this means that if people aren't looking at the warning or hard erroring on warnings then we're going to emit bad code instead of making it an error.</div><span class="HOEnZb"><font color="#888888"><div>
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-eric</div></font></span></div><br></div></div>
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