<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Dec 10, 2015, at 8:09 AM, Daniel Berlin via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" class="">llvm-dev@lists.llvm.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class=""><div class="gmail_extra"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr" class=""><div class="gmail_extra"><div class="gmail_quote"><span class=""><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div dir="ltr" class=""><div class="gmail_extra"><div class="gmail_quote"><div class=""><br class=""></div></div></div></div></blockquote></span><div class="">Opps, you are right in my example basicaaa could do it potentially. Correct example is slightly different:</div><span class=""><div class="">int foo(struct S *ps, int i) {<br class=""></div></span><div class=""><span class=""><div class=""> ps->a[i] = 1;</div><div class=""> ps->b = 2;</div></span><div class=""> return ps->a[i];</div><div class="">}</div></div><div class="">Here basicaa cannot make sure that 'ps->a[i]' doesn't change after 'ps->b = 2' because if 'i == 10' all 3 memory accesses will read/write the same memory. And type information about S::a is required to disambiguate. With current TBAA 'ps->a[i]' is about random 'int' read.</div></div></div></div></blockquote><div class=""><br class=""></div><div class="">Yes, and without more info, in LLVM that read can legally touch ps->b.</div></div></div></div></div></blockquote>I thought the inbounds on the GEPs would have told us that the a[] accesses and b access are both in bounds of their respective fields of the struct.</div><div><br class=""></div><div>Or does inbounds only tell us that the GEPs are in bounds of ‘ps’ itself?</div><div><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div class="gmail_extra"><div class="gmail_quote"><div class="">So that makes sense.</div><div class=""> <br class=""></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr" class=""><div class="gmail_extra"><div class="gmail_quote"><span class=""><div class=""> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div dir="ltr" class=""><div class="gmail_extra"><div class="gmail_quote"><span class=""><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div dir="ltr" class=""><div class="">Missing information here is the range inside struct S that could be accessed. </div></div></blockquote><div class=""><br class=""></div></span><div class="">What do you mean by "could be accessed". Do you mean "valid to access in C"?</div></div></div></div></blockquote><div class=""><br class=""></div></span><div class="">By access I meant read/write memory i.e. that size of S::a inside the struct or at least information that only S::a is accessed in this place i.e. not S::b.</div></div></div></div></blockquote><div class=""><br class=""></div><div class="">Okay.</div><div class=""><br class=""></div><div class="">So what you want sounds reasonable to me ;-)</div><div class=""><br class=""></div></div></div></div>
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