On Fri, Jun 21, 2024 at 10:21 AM Richard Sandiford
<[email protected]> wrote:
>
> Richard Biener <[email protected]> writes:
> > [...]
> > I wonder if you can amend doc/passes.texi, specifically noting differences
> > between fwprop, combine and late-combine?
>
> Ooh, we have a doc/passes.texi? :) Somehow missed that.
Yeah, I also usually forget this.
> How about the patch below?
Thanks - looks good to me.
Richard.
> Thanks,
> Richard
>
>
> diff --git a/gcc/doc/passes.texi b/gcc/doc/passes.texi
> index 5746d3ec636..4ac7a2306a1 100644
> --- a/gcc/doc/passes.texi
> +++ b/gcc/doc/passes.texi
> @@ -991,6 +991,25 @@ RTL expressions for the instructions by substitution,
> simplifies the
> result using algebra, and then attempts to match the result against
> the machine description. The code is located in @file{combine.cc}.
>
> +@item Late instruction combination
> +
> +This pass attempts to do further instruction combination, on top of
> +that performed by @file{combine.cc}. Its current purpose is to
> +substitute definitions into all uses simultaneously, so that the
> +definition can be removed. This differs from the forward propagation
> +pass, whose purpose is instead to simplify individual uses on the
> +assumption that the definition will remain. It differs from
> +@file{combine.cc} in that there is no hard-coded limit on the number
> +of instructions that can be combined at once. It also differs from
> +@file{combine.cc} in that it can move instructions, where necessary.
> +
> +However, the pass is not in principle limited to this form of
> +combination. It is intended to be a home for other, future
> +combination approaches as well.
> +
> +The pass runs twice, once before register allocation and once after
> +register allocation. The code is located in @file{late-combine.cc}.
> +
> @item Mode switching optimization
>
> This pass looks for instructions that require the processor to be in a
