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[PATCH] PR tree-optimization/94026: Simplify (X>>8)&6 != 0 as X&1536 != 0.

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This patch implements the missed optimization described in PR 94026,
where a the shift can be eliminated from the sequence of a shift,
followed by a bit-wise AND followed by an equality/inequality test.
Specifically, ((X << C1) & C2) cmp C3 into (X & (C2 >> C1)) cmp (C3 >> C1)
and likewise ((X >> C1) & C2) cmp C3 into (X & (C2 << C1)) cmp (C3 << C1)
where cmp is == or !=, and C1, C2 and C3 are integer constants.
The example in the subject line is taken from the hot function
self_atari from the Go program Leela (in SPEC CPU 2017).

2022-06-27  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	PR tree-optimization/94026
	* match.pd (((X << C1) & C2) eq/ne C3): New simplification.
	(((X >> C1) & C2) eq/ne C3): Likewise.

gcc/testsuite/ChangeLog
	PR tree-optimization/94026
	* gcc.dg/pr94026.c: New test case.
This commit is contained in:
Roger Sayle 2022-06-27 07:44:49 +01:00
parent 2ae7895416
commit f3f73e86ec
2 changed files with 44 additions and 0 deletions
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23
gcc/match.pd
View file

@ -3572,6 +3572,29 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
&& wi::lshift (wi::to_wide (@0), cand) == wi::to_wide (@2))
(cmp @1 { build_int_cst (TREE_TYPE (@1), cand); }))))))
/* Fold ((X << C1) & C2) cmp C3 into (X & (C2 >> C1)) cmp (C3 >> C1)
((X >> C1) & C2) cmp C3 into (X & (C2 << C1)) cmp (C3 << C1). */
(for cmp (ne eq)
(simplify
(cmp (bit_and:s (lshift:s @0 INTEGER_CST@1) INTEGER_CST@2) INTEGER_CST@3)
(if (tree_fits_shwi_p (@1)
&& tree_to_shwi (@1) > 0
&& tree_to_shwi (@1) < TYPE_PRECISION (TREE_TYPE (@0))
&& tree_to_shwi (@1) <= wi::ctz (wi::to_wide (@3)))
(with { wide_int c1 = wi::to_wide (@1);
wide_int c2 = wi::lrshift (wi::to_wide (@2), c1);
wide_int c3 = wi::lrshift (wi::to_wide (@3), c1); }
(cmp (bit_and @0 { wide_int_to_tree (TREE_TYPE (@0), c2); })
{ wide_int_to_tree (TREE_TYPE (@0), c3); }))))
(simplify
(cmp (bit_and:s (rshift:s @0 INTEGER_CST@1) INTEGER_CST@2) INTEGER_CST@3)
(if (tree_fits_shwi_p (@1)
&& tree_to_shwi (@1) > 0
&& tree_to_shwi (@1) < TYPE_PRECISION (TREE_TYPE (@0))
&& tree_to_shwi (@1) <= wi::clz (wi::to_wide (@2))
&& tree_to_shwi (@1) <= wi::clz (wi::to_wide (@3)))
(cmp (bit_and @0 (lshift @2 @1)) (lshift @3 @1)))))
/* Fold (X << C1) & C2 into (X << C1) & (C2 | ((1 << C1) - 1))
(X >> C1) & C2 into (X >> C1) & (C2 | ~((type) -1 >> C1))
if the new mask might be further optimized. */

21
gcc/testsuite/gcc.dg/pr94026.c Normal file
View file

@ -0,0 +1,21 @@
/* { dg-do compile } */
/* { dg-options "-O2 -fdump-tree-optimized" } */
int f1(int x) { return ((x >> 8) & 6) != 0; }
int f2(int x) { return ((x << 2) & 24) != 0; }
int f3(unsigned x) { return ((x << 2) & 15) != 0; }
int f4(unsigned x) { return ((x >> 2) & 14) != 0; }
int fifth (int c)
{
int a = (c >> 8) & 7;
if (a >= 2) {
return 1;
} else {
return 0;
}
}
/* { dg-final { scan-tree-dump-not " << " "optimized" } } */
/* { dg-final { scan-tree-dump-not " >> " "optimized" } } */