[PATCH] CodeGenPrepare: Avoid and/or i1 in select conditions.

hfinkel at anl.gov hfinkel at anl.gov
Fri Feb 6 11:43:30 PST 2015

In http://reviews.llvm.org/D7399#119931, @MatzeB wrote:

> On a side note: Ahmed just mentioned a snipped from SelectionDAGBuilder to me that has pretty much the same logic I do for selects implemented for branches:
>   // If this is a series of conditions that are or'd or and'd together, emit
>    // this as a sequence of branches instead of setcc's with and/or operations.
>    // As long as jumps are not expensive, this should improve performance.
>    // For example, instead of something like:
>    //     cmp A, B
>    //     C = seteq
>    //     cmp D, E
>    //     F = setle
>    //     or C, F
>    //     jnz foo
>    // Emit:
>    //     cmp A, B
>    //     je foo
>    //     cmp D, E
>    //     jle foo
>    //
> ...
> no idea why that is in SelectionDAGBuilder, it also doesn't seem strictly beneficial to all targets to me...

It's not (and it was pointed out to me in a different thread a couple of months ago); which function does this again? I keep forgetting to fix this... (my current plan is to turn it off when TLI->hasMultipleConditionRegisters() is true, which is only the case on PPC AFAIK).




More information about the llvm-commits mailing list