> On Dec 4, 2015, at 9:06 AM, Erik Eckstein <[email protected]> wrote: > > Hi, > > currently some instructions, like alloc_stack and alloc_box (I think they are > the only ones) return 2 values. For this we have the "result number" in > SILValue, e.g. %3#0, %3#1 > > We could represent the same by using a projection instruction, e.g. > > %3 = alloc_stack $Type // == the old %3#0 > %4 = project_stack %1 // == the old %3#1 > > And actually we already have the project_box instruction. > > This would simplify SILValues and many places in optimization > passes/analysis. Yesterday I spent several hours to debug a problem where in > some pass the wrong result number was used. > > What do you think?
Like John said, this would cause us to generate a lot more SIL IR, and potentially more LLVM IR as well, since the projected address is produced as part of the lowering of alloc_stack and alloc_box. Multiple values are handy for things like alloc_stack and alloc_box where both values are immediately used in the common case. Looking forward, I think we'd also like function applications to be able to produce arbitrarily many values at the SIL level, which would save a bunch of tuple imploding and exploding that's currently necessary. -Joe _______________________________________________ swift-dev mailing list [email protected] https://lists.swift.org/mailman/listinfo/swift-dev
