On 11/10/2021 11:20 AM, Aldy Hernandez via Gcc-patches wrote:
As discussed in the PR, the loop header copying pass avoids doing so
when optimizing for size. However, sometimes we can determine the
loop entry conditional statically for the first iteration of the loop.
This patch uses the path solver to determine the outgoing edge
out of preheader->header->xx. If so, it allows header copying. Doing
this in the loop optimizer saves us from doing gymnastics in the
threader which doesn't have the context to determine if a loop
transformation is profitable.
I am only returning true in entry_loop_condition_is_static for
a true conditional. Technically a false conditional is also
provably static, but allowing any boolean value causes a regression
in gfortran.dg/vector_subscript_1.f90.
I would have preferred not passing around the query object, but the
layout of pass_ch and should_duplicate_loop_header_p make it a bit
awkward to get it right without an outright refactor to the
pass.
Tested on x86-64 Linux.
OK?
gcc/ChangeLog:
PR tree-optimization/102906
* tree-ssa-loop-ch.c (entry_loop_condition_is_static): New.
(should_duplicate_loop_header_p): Call entry_loop_condition_is_static.
(class ch_base): Add m_ranger and m_query.
(ch_base::copy_headers): Pass m_query to
entry_loop_condition_is_static.
(pass_ch::execute): Allocate and deallocate m_ranger and
m_query.
(pass_ch_vect::execute): Same.
gcc/testsuite/ChangeLog:
* gcc.dg/tree-ssa/pr102906.c: New test.
OK. It also makes a nice little example of how to use a Ranger within
an existing pass.
Jeff
