<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br><div><div>On Aug 25, 2008, at 3:24 PM, Nick Kledzik wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br><div><div>On Aug 22, 2008, at 4:40 PM, Devang Patel wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0; "><div><font class="Apple-style-span" face="Courier">The LLVM passes are responsible to take appropriate actions based on Function </font></div><div><font class="Apple-style-span" face="Courier">Notes associated with function definition. For example, </font></div><div><font class="Apple-style-span" face="Courier"><br></font></div><div><font class="Apple-style-span" face="Courier">define void @fn1() notes("opt-size=1") { ... }</font></div><div><font class="Apple-style-span" face="Courier"><br></font></div><div><font class="Apple-style-span" face="Courier">The function fn1() is being optimized for size without losing significant </font></div><div><font class="Apple-style-span" face="Courier">performance. The inliner will update inlining threshold for fn1() such that the </font></div><div><font class="Apple-style-span" face="Courier">functions called by fn1() are checked for size threshold for fn1() while being </font></div><div><font class="Apple-style-span" face="Courier">inlined inside fn1(). If the function fn1() is itself inlined somewhere, for </font></div><div><font class="Apple-style-span" face="Courier">example bar(), then the inlining threshold for bar() will be the deciding factor. </font></div><div><font class="Apple-style-span" face="Courier"><br></font></div><div><font class="Apple-style-span" face="Courier">define void @fn2() notes("opt-size=2") { ... }</font></div><div><font class="Apple-style-span" face="Courier"><br></font></div><div><font class="Apple-style-span" face="Courier">The function fn2() is aggressively optimized for size. The code generator may </font></div><div><font class="Apple-style-span" face="Courier">sacrifice performance while selecting instructions. The inliner will aggressively </font></div><div><font class="Apple-style-span" face="Courier">reduce inlining threshold.</font></div><div><font class="Apple-style-span" face="Courier"><br></font></div><div><font class="Apple-style-span" face="Courier">define void @fn3() notes("noinline") { ... }</font></div><div><font class="Apple-style-span" face="Courier">define void @fn4() notes("always_inline") { ... }</font></div><div><font class="Apple-style-span" face="Courier">define void @fn5() notes("noinline,always_inline") { ... }</font></div></span></blockquote><blockquote type="cite"><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0; "><div><font class="Apple-style-span" face="Courier"><br></font></div><div><font class="Apple-style-span" face="Courier">Here the inliner is instructed to not inline function fn3() anywhere and inline </font></div><div><font class="Apple-style-span" face="Courier">function fn4() everywhere. The function fn5() is malformed and it should be </font></div><div><font class="Apple-style-span" face="Courier">rejected by the verifier.</font></div></span></blockquote></div><br><div><div>Since you opened the door with values for opt-size, couldn't we do the same for inlining. That is:</div><div><div><font class="Apple-style-span" face="Courier"><br></font></div><div><font class="Apple-style-span" face="Courier"> define void @fn3() notes("inline=never") { ... }</font></div><div><font class="Apple-style-span" face="Courier"> define void @fn4() notes("inline=always") { ... }</font></div><div><font class="Apple-style-span" face="Courier"><br></font></div></div><div>Then the general rule is that there can be only one "foo=" in the set of notes. </div></div></div></blockquote><div><br></div><div>yes! I did not think about this. This is a good idea.</div><br><blockquote type="cite"><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><div> I know this won't make the __attribute__ keywords, but it would make the function notes cleaner.</div><div><br></div><div>Also, could there be a name for 1 and 2 on opt-size? What happens when we find a need for a third kind of opt-size...</div><div><br></div><div><br></div><div>These seem like great default parameters for code-gen, but looking forward, if we also allowed some optimization flags to be specified at LTO time, how would they interact? </div></div></div></blockquote><br></div><div>The flags specified on the linker command line during LTO are not encoded into llvm IR. However, IMO, these linker command line flags should override notes encoded in llvm IR. We may have to handle special cases, but we should document linker's decision choices properly.</div><div><br></div><div>-</div><div>Devang</div><div><br></div><br></body></html>