https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106701
rdapp at gcc dot gnu.org changed:
What |Removed |Added
----------------------------------------------------------------------------
Target|s390 |s390 x86_64-linux-gnu
CC| |glisse at gcc dot gnu.org,
| |rdapp at gcc dot gnu.org,
| |rguenth at gcc dot gnu.org
Summary|s390: Compiler does not |Compiler does not take into
|take into account number |account number range
|range limitation to avoid |limitation to avoid
|subtract from immediate |subtract from immediate
--- Comment #1 from rdapp at gcc dot gnu.org ---
Added x86 to targets because we don't seem to optimize this there either (at
least I didn't see it on my recent-ish GCC).
The following (not regtested) helps on s390
diff --git a/gcc/match.pd b/gcc/match.pd
index e486b4be282c..2ebbf68010f9 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -7992,3 +7992,27 @@ and,
(match (bitwise_induction_p @0 @2 @3)
(bit_not
(nop_convert1? (bit_xor@0 (convert2? (lshift integer_onep@1 @2)) @3))))
+
+/* cst - a -> cst ^ a if 0 >= a <= cst and integer_pow2p (cst + 1). */
+#if GIMPLE
+(simplify
+ (minus INTEGER_CST@0 @1)
+ (with {
+ wide_int w = wi::to_wide (@0) + 1;
+ value_range vr;
+ wide_int wmin = w;
+ wide_int wmax = w;
+ if (get_global_range_query ()->range_of_expr (vr, @1)
+ && vr.kind () == VR_RANGE)
+ {
+ wmin = vr.lower_bound ();
+ wmax = vr.upper_bound ();
+ }
+ }
+ (if (wi::exact_log2 (w) != -1
+ && wi::geu_p (wmin, 0)
+ && wi::leu_p (wmax, w))
+ (bit_xor @0 @1))
+ )
+)
+#endif
but it can surely be improved by some match.pd magic still. A second question
would be, do we unconditionally want to simplify this or should it rather be
backend dependent?
