From bc5fca4cbafae6b6bbf55787af1d2e5d1538649b Mon Sep 17 00:00:00 2001 From: Eugene Rozenfeld Date: Fri, 23 Oct 2020 16:47:01 -0700 Subject: [PATCH] Add a tree optimization described in PR97223. MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Convert x < (short) ((unsigned short)x + const) to x <= SHORT_MAX – const (and similarly for other integral types) if const is not 0. For example, without this patch the x86_64-pc-linux code generated for this function bool f(char x) { return x < (char)(x + 12); } is lea eax,[rdi+0xc] cmp al,dil setg al ret With the patch the code is cmp dil,0x73 setle al ret --- gcc/match.pd | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/gcc/match.pd b/gcc/match.pd index 17ba04100c7..bc5bed626ec 100644 --- a/gcc/match.pd +++ b/gcc/match.pd @@ -4954,6 +4954,22 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT) wi::max_value (prec, UNSIGNED) - wi::to_wide (@1)); }))))) +/* Similar to the previous pattern but with additional casts. */ +(for cmp (lt le ge gt) + out (gt gt le le) + (simplify + (cmp:c (convert@3 (plus@2 (convert@4 @0) INTEGER_CST@1)) @0) + (if (!TYPE_UNSIGNED (TREE_TYPE (@0)) + && types_match (TREE_TYPE (@0), TREE_TYPE (@3)) + && types_match (TREE_TYPE (@4), unsigned_type_for (TREE_TYPE (@0))) + && TYPE_OVERFLOW_WRAPS (TREE_TYPE (@4)) + && wi::to_wide (@1) != 0 + && single_use (@2)) + (with { unsigned int prec = TYPE_PRECISION (TREE_TYPE (@0)); } + (out @0 { wide_int_to_tree (TREE_TYPE (@0), + wi::max_value (prec, SIGNED) + - wi::to_wide (@1)); }))))) + /* To detect overflow in unsigned A - B, A < B is simpler than A - B > A. However, the detection logic for SUB_OVERFLOW in tree-ssa-math-opts.c expects the long form, so we restrict the transformation for now. */ -- 2.17.1