<html> <head> <base href="https://bugs.freedesktop.org/" /> </head> <body> <div> <a class="bz_bug_link bz_status_NEW " title="NEW - [llvmpipe] piglit gl-1.0-dlist-beginend failure with llvm-3.6.0svn" href="https://bugs.freedesktop.org/show_bug.cgi?id=85467#c1">Comment # 1</a> on <a class="bz_bug_link bz_status_NEW " title="NEW - [llvmpipe] piglit gl-1.0-dlist-beginend failure with llvm-3.6.0svn" href="https://bugs.freedesktop.org/show_bug.cgi?id=85467">bug 85467</a> from <a class="email" href="mailto:vlee@freedesktop.org" title="Vinson Lee <vlee@freedesktop.org>"> Vinson Lee</a> <pre>This is introduced with llvm-3.6.0svn r220138. 9b2d091a9c2509a766a233a64453462faa2bdffc is the first bad commit commit 9b2d091a9c2509a766a233a64453462faa2bdffc Author: Chandler Carruth <<a href="mailto:chandlerc@gmail.com">chandlerc@gmail.com</a>> Date: Sat Oct 18 06:36:22 2014 +0000 [InstCombine] Do an about-face on how LLVM canonicalizes (cast (load ...)) and (load (cast ...)): canonicalize toward the former. Historically, we've tried to load using the type of the *pointer*, and tried to match that type as closely as possible removing as many pointer casts as we could and trading them for bitcasts of the loaded value. This is deeply and fundamentally wrong. Repeat after me: memory does not have a type! This was a hard lesson for me to learn working on SROA. There is only one thing that should actually drive the type used for a pointer, and that is the type which we need to use to load from that pointer. Matching up pointer types to the loaded value types is very useful because it minimizes the physical size of the IR required for no-op casts. Similarly, the only thing that should drive the type used for a loaded value is *how that value is used*! Again, this minimizes casts. And in fact, the *only* thing motivating types in any part of LLVM's IR are the types used by the operations in the IR. We should match them as closely as possible. I've ended up removing some tests here as they were testing bugs or behavior that is no longer present. Mostly though, this is just cleanup to let the tests continue to function as intended. The only fallout I've found so far from this change was SROA and I have fixed it to not be impeded by the different type of load. If you find more places where this change causes optimizations not to fire, those too are likely bugs where we are assuming that the type of pointers is "significant" for optimization purposes. git-svn-id: <a href="https://llvm.org/svn/llvm-project/llvm/trunk@220138">https://llvm.org/svn/llvm-project/llvm/trunk@220138</a> 91177308-0d34-0410-b5e6-96231b3b80d8 :040000 040000 982ecfc2706221c9731e5e8f54346370d2fe6283 667a68ea436b53840beda4b034cceee0e87dc6eb M lib :040000 040000 a6f61cd09e99c468c8fdb8dd6bda10060b4f751f cad7ad5d09cf0f43b3f47e36050c833b2debc9fc M test bisect run success</pre> </div> <hr> You are receiving this mail because: <ul> <li>You are the assignee for the bug.</li> </ul> </body> </html>