On 03/02/2018 04:07 PM, Jakub Jelinek wrote: > On Fri, Mar 02, 2018 at 03:18:05PM -0700, Jeff Law wrote: >> On 02/28/2018 03:43 AM, Richard Biener wrote: >> [ More snipping ] >> >>> >>>> It's actually pretty easy to fix the CFG. We just need to recognize >>>> that a "returns twice" function returns not to the call, but to the >>>> point immediately after the call. So if we have a call to a returns >>>> twice function that ends a block with a single successor, when we wire >>>> up the abnormal dispatcher, we target the single successor rather than >>>> the block containing the returns-twice call. >>> >>> Hmm, I think you need to check whether the successor has a single >>> predecessor, not whether we have a single successor (we always have >>> that unless setjmp also throws). If you fix that you keep the CFG >>> "incorrect" if there are multiple predecessors so I think in addition >>> to properly creating the edges you have to work on the BB building >>> part to ensure that there's a single-predecessor block after >>> returns-twice function calls. Note that currently we force returns-twice >>> to be the first (and only) stmt of a block -- your fix would relax this, >>> returns-twice no longer needs to start a new BB. >> So I found the code which makes the setjmp start a new block. But I >> haven't found the code which makes setjmp end a block. I'm going to >> have to throw things into the debugger to find the latter. >> >> >> We ought to remove the code that makes the setjmp start a new block. >> That's just unnecessary. setjmp certainly needs to end the block though. > > At least in gimple, having setjmp start the block is intentional; > we have abnormal edges from all the (possible) spots which might have > longjmp to abnormal dispatcher artificial bb and from that block abnormal > edges to all the sigjmp starts, which is how we emulate the fact that > longjmp might return in a setjmp location. Edges are created by > handle_abnormal_edges. But the longjmp should not return to the setjmp call, it should return to the point immediately after the setjmp call. That's the core of the issue with 61118.
jeff
