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Stop backwards thread discovery when leaving a loop

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The backward threader copier cannot deal with the situation of
copying blocks belonging to different loops and will reject those
paths late.  The following uses this to prune path discovery,
saving on compile-time.  Note the off-loop block is still considered
as entry edge origin.

	* tree-ssa-threadbackward.cc (back_threader::find_paths_to_names):
	Do not walk further if we are leaving the current loop.
This commit is contained in:
Richard Biener 2022-08-16 14:14:55 +02:00
parent 2b403297b1
commit 9594e04e4e
1 changed files with 6 additions and 0 deletions
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6
gcc/tree-ssa-threadbackward.cc
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@ -355,6 +355,12 @@ back_threader::find_paths_to_names (basic_block bb, bitmap interesting,
|| maybe_register_path ()))
;
// The backwards thread copier cannot copy blocks that do not belong
// to the same loop, so when the new source of the path entry no
// longer belongs to it we don't need to search further.
else if (m_path[0]->loop_father != bb->loop_father)
;
// Continue looking for ways to extend the path but limit the
// search space along a branch
else if ((overall_paths = overall_paths * EDGE_COUNT (bb->preds))