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match.pd handling of three-constant bitops
- From: Richard Sandiford <richard dot sandiford at linaro dot org>
- To: gcc-patches at gcc dot gnu dot org
- Date: Wed, 20 Sep 2017 13:18:39 +0100
- Subject: match.pd handling of three-constant bitops
- Authentication-results: sourceware.org; auth=none
natch.pd tries to reassociate two bit operations if both of them have
constant operands. However, with the polynomial integers added later,
there's no guarantee that a bit operation on two integers can be folded
at compile time. This means that the pattern can trigger for operations
on three constants, and as things stood could endlessly oscillate
between the two associations.
This patch keeps the existing pattern for the normal case of a
non-constant first operand. When all three operands are constant it
tries to find a pair of constants that do fold. If none do, it keeps
the original expression as-was.
Tested on aarch64-linux-gnu, x86_64-linux-gnu and powerpc64le-linus-gnu.
OK to install?
Richard
2017-09-20 Richard Sandiford <richard.sandiford@linaro.org>
Alan Hayward <alan.hayward@arm.com>
David Sherwood <david.sherwood@arm.com>
gcc/
* match.pd: Handle bit operations involving three constants
and try to fold one pair.
Index: gcc/match.pd
===================================================================
--- gcc/match.pd 2017-09-16 21:38:21.106513157 +0100
+++ gcc/match.pd 2017-09-20 13:17:10.552389270 +0100
@@ -1017,7 +1017,14 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(for bitop (bit_and bit_ior bit_xor)
(simplify
(bitop (bitop @0 CONSTANT_CLASS_P@1) CONSTANT_CLASS_P@2)
- (bitop @0 (bitop @1 @2))))
+ (if (!CONSTANT_CLASS_P (@0))
+ (bitop @0 (bitop @1 @2))
+ (with { tree cst1 = const_binop (bitop, type, @0, @2); }
+ (if (cst1)
+ (bitop @1 { cst1; })
+ (with { tree cst2 = const_binop (bitop, type, @1, @2); }
+ (if (cst2)
+ (bitop @0 { cst2; }))))))))
/* Try simple folding for X op !X, and X op X with the help
of the truth_valued_p and logical_inverted_value predicates. */