Richard Biener <richard.guent...@gmail.com> 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.
How about the patch below?
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
