On Apr 5, 2010, Jeff Law <l...@redhat.com> wrote: > We accomplish this by emitting a load from memory into a new pseudo > before the first use of P in a region and a store from the new pseudo > back to memory after the last assignment to P within the region, then > we rename all references from P to P'. It's marginally more complex, > but I think for this discussion the other complexities can be ignored. > After all regions have been processed, P is gone from the insn stream. > Obviously P can be found in memory, P1, P2, ... Pn depending on > precisely where we are in the code when the value is P is requested.
I can think of 3 points that you might have to be concerned about: 1. Don't pay attention to debug insns when computing the live ranges. You don't want to take debug insns into account when making decisions about transformations to executable code. 2. When renaming references from P to P' in a region, do take debug insns in the region into account, renaming references in debug insns as you would in any other insn. 3. If any debug insns ended up outside any of the regions determined without taking debug insns into account, you may have to patch things up so that they don't remain as dangling pointers to P. From your description above, it appears to me that replacing such remaining references to P in debug insns with the memory slot assigned to it would be the right thing to do. This should be all, and it's very much in line with “The Zen of VTA”: disregard debug insns when deciding what to do, transform debug insns just as you would regular insns, and patch up any debug insns left out of the decisions you made. -- Alexandre Oliva, freedom fighter http://FSFLA.org/~lxoliva/ You must be the change you wish to see in the world. -- Gandhi Be Free! -- http://FSFLA.org/ FSF Latin America board member Free Software Evangelist Red Hat Brazil Compiler Engineer
