On Tue, Aug 30, 2016 at 12:40 AM, Matt Turner <matts...@gmail.com> wrote: > On Mon, Aug 29, 2016 at 9:06 PM, Timothy Arceri > <timothy.arc...@collabora.com> wrote: >> Can't the phi have more than one source from before the loop? e.g >> >> int i = 0; >> if (somthing) >> i = 1; >> else >> i = 2; >> >> for ( ; i < 5; i++) >> do_stuff(i); > > In fact, no. :) > > NIR's control flow avoids so-called "critical edges" by ensuring that > all if/else must be preceded by a single basic block and followed by a > single basic block. It simplifies a lot of situations. This invariant > and a few more are documented at the top of nir_control_flow.c. > > In your example, there will be a basic block between the end of the > if/else construct and the beginning of the loop which will contain a > phi node for i. > > phi nodes only have as many sources as its containing basic block has > incoming edges. There are only two ways (that I can think of) that a > block may have more than two incoming edges in NIR: multiple break or > continue statements in a loop.
Matt is exactly right here... FWIW, I wrote up more details on NIR control flow at https://people.freedesktop.org/~cwabbott0/nir-docs/control_flow.html#the-nir-control-flow-model (although I need to rebase my series and update the control flow modification part... hmm). _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev
