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| author | Segher Boessenkool <segher@kernel.crashing.org> | 2015-10-11 11:03:09 +0200 |
|---|---|---|
| committer | Segher Boessenkool <segher@gcc.gnu.org> | 2015-10-11 11:03:09 +0200 |
| commit | c70f0ca26b5843498c2d1258865c77b1da545e27 (patch) | |
| tree | 04a5840f8567588820334a1cb08eabe841a9300d /gcc | |
| parent | fac812f0bdd174e727899f2557580418ccf62c55 (diff) | |
| download | gcc-c70f0ca26b5843498c2d1258865c77b1da545e27.zip gcc-c70f0ca26b5843498c2d1258865c77b1da545e27.tar.gz gcc-c70f0ca26b5843498c2d1258865c77b1da545e27.tar.bz2 | |
bb-reorder: Improve the simple algorithm for -Os (PR67864)
As the PR points out, the "simple" reorder algorithm makes bigger code
than the STC algorithm did, for -Os, for x86. I now tested it for many
different targets and it turns out to be worse everywhere.
This simple patch tunes "simple" a bit; this makes it better than STC
almost everywhere. The only exceptions (for the targets where I have
results) are x86 and mn10300. For those targets it may be best to switch
the default algorithm for -Os to STC.
2015-10-11 Segher Boessenkool <segher@kernel.crashing.org>
PR rtl-optimization/67864
* gcc/bb-reorder (reorder_basic_blocks_simple): Prefer existing
fallthrough edges for conditional jumps. Don't sort candidate
edges if not optimizing for speed.
From-SVN: r228692
Diffstat (limited to 'gcc')
| -rw-r--r-- | gcc/ChangeLog | 7 | ||||
| -rw-r--r-- | gcc/bb-reorder.c | 16 |
2 files changed, 19 insertions, 4 deletions
diff --git a/gcc/ChangeLog b/gcc/ChangeLog index 0599481..3cc9c5c 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,10 @@ +2015-10-11 Segher Boessenkool <segher@kernel.crashing.org> + + PR rtl-optimization/67864 + * gcc/bb-reorder (reorder_basic_blocks_simple): Prefer existing + fallthrough edges for conditional jumps. Don't sort candidate + edges if not optimizing for speed. + 2015-10-10 Trevor Saunders <tbsaunde+gcc@tbsaunde.org> * defaults.h (REVERSE_CONDITION): New default definition. diff --git a/gcc/bb-reorder.c b/gcc/bb-reorder.c index cb001e8..3b7098e 100644 --- a/gcc/bb-reorder.c +++ b/gcc/bb-reorder.c @@ -2318,16 +2318,24 @@ reorder_basic_blocks_simple (void) if (any_condjump_p (end)) { - edges[n++] = EDGE_SUCC (bb, 0); - edges[n++] = EDGE_SUCC (bb, 1); + edge e0 = EDGE_SUCC (bb, 0); + edge e1 = EDGE_SUCC (bb, 1); + /* When optimizing for size it is best to keep the original + fallthrough edges. */ + if (e1->flags & EDGE_FALLTHRU) + std::swap (e0, e1); + edges[n++] = e0; + edges[n++] = e1; } else if (single_succ_p (bb)) edges[n++] = EDGE_SUCC (bb, 0); } - /* Sort the edges, the most desirable first. */ + /* Sort the edges, the most desirable first. When optimizing for size + all edges are equally desirable. */ - std::stable_sort (edges, edges + n, edge_order); + if (optimize_function_for_speed_p (cfun)) + std::stable_sort (edges, edges + n, edge_order); /* Now decide which of those edges to make fallthrough edges. We set BB_VISITED if a block already has a fallthrough successor assigned |