<html><head><meta http-equiv="Content-Type" content="text/html charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><div></div><br><div><div>On Dec 21, 2012, at 4:04 PM, Quentin Colombet <<a href="mailto:qcolombet@apple.com">qcolombet@apple.com</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">Hi Nick,<br><br>On Dec 21, 2012, at 3:59 PM, Dmitri Gribenko <<a href="mailto:gribozavr@gmail.com">gribozavr@gmail.com</a>> wrote:<br><br><blockquote type="cite">On Sat, Dec 22, 2012 at 1:53 AM, Nick Lewycky <<a href="mailto:nicholas@mxc.ca">nicholas@mxc.ca</a>> wrote:<br><blockquote type="cite">On 12/21/2012 03:43 PM, Quentin Colombet wrote:<br><blockquote type="cite"><br>Hi,<br><br>Here is a patch to help llvm turning a code like this:<br>if (foo)<br>free(foo)<br><br>into that:<br>free(foo)<br><br>It is legal and safe, since free is already checking its argument<br>against NULL internally (I may find the reference in the Standard if<br>needed :)).<br></blockquote><br>It's legal and safe, but is it desirable? Calling a function is expensive<br>even if the function doesn't do anything.<br></blockquote></blockquote><br>Yes, you're right, it may not be desirable but I'm tempt to think like Dmitri.<br><br>Do you think that this optimization should be controlled by a flag?<br>At least, for code size (Oz and maybe Os), it may always be desirable.<br><br>I did not consider changing free(foo) into if(foo) free(foo)<br><br><blockquote type="cite"><br>That's true, but there's another viewpoint: programmers usually write<br>'if(!foo) free(foo);' not because they are manually inlining the fast<br>path of free(), but because they think that free(NULL) is UB.<br><br>Dmitri<br><br>-- <br>main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if<br>(j){printf("%d\n",i);}}} /*Dmitri Gribenko <<a href="mailto:gribozavr@gmail.com">gribozavr@gmail.com</a>>*/<br></blockquote><br>_______________________________________________<br>llvm-commits mailing list<br><a href="mailto:llvm-commits@cs.uiuc.edu">llvm-commits@cs.uiuc.edu</a><br>http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits<br></blockquote></div><br></div></body></html>