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| author | guojiufu <guojiufu@linux.ibm.com> | 2020-10-19 13:48:19 +0800 |
|---|---|---|
| committer | guojiufu <guojiufu@linux.ibm.com> | 2020-10-19 17:26:41 +0800 |
| commit | 222f312a773157f53396ba4cb287deb07f84cc34 (patch) | |
| tree | d865a929bc4d8d6f467ce98e33831931f4a50451 /gcc | |
| parent | dccb0f8801363462a11fd13a33ff3f4092ff82bd (diff) | |
| download | gcc-222f312a773157f53396ba4cb287deb07f84cc34.zip gcc-222f312a773157f53396ba4cb287deb07f84cc34.tar.gz gcc-222f312a773157f53396ba4cb287deb07f84cc34.tar.bz2 | |
[PATCH] fold x << (n % C) to x << (n & C-1) if C meets power2
This patch fixes PR66552 which is also as:
https://gcc.gnu.org/pipermail/gcc-patches/2020-February/540930.html
which requests to optimizes (x shift (n mod C)) to
(x shift (n bit_and (C - 1))) when C is a constant and power of two.
gcc/ChangeLog
2020-10-19 Li Jia He <helijia@gcc.gnu.org>
PR tree-optimization/66552
* match.pd (x << (n % C) -> x << (n & C-1)): New simplification.
gcc/testsuite/ChangeLog
2020-10-19 Li Jia He <helijia@gcc.gnu.org>
PR tree-optimization/66552
* gcc.dg/pr66552.c: New testcase.
Diffstat (limited to 'gcc')
| -rw-r--r-- | gcc/match.pd | 12 | ||||
| -rw-r--r-- | gcc/testsuite/gcc.dg/pr66552.c | 14 |
2 files changed, 25 insertions, 1 deletions
diff --git a/gcc/match.pd b/gcc/match.pd index a7032dc..17ba041 100644 --- a/gcc/match.pd +++ b/gcc/match.pd @@ -607,12 +607,22 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT) /* Optimize TRUNC_MOD_EXPR by a power of two into a BIT_AND_EXPR, i.e. "X % C" into "X & (C - 1)", if X and C are positive. Also optimize A % (C << N) where C is a power of 2, - to A & ((C << N) - 1). */ + to A & ((C << N) - 1). + Also optimize "A shift (B % C)", if C is a power of 2, to + "A shift (B & (C - 1))". SHIFT operation include "<<" and ">>" + and assume (B % C) is nonnegative as shifts negative values would + be UB. */ (match (power_of_two_cand @1) INTEGER_CST@1) (match (power_of_two_cand @1) (lshift INTEGER_CST@1 @2)) (for mod (trunc_mod floor_mod) + (for shift (lshift rshift) + (simplify + (shift @0 (mod @1 (power_of_two_cand@2 @3))) + (if (integer_pow2p (@3) && tree_int_cst_sgn (@3) > 0) + (shift @0 (bit_and @1 (minus @2 { build_int_cst (TREE_TYPE (@2), + 1); })))))) (simplify (mod @0 (convert?@3 (power_of_two_cand@1 @2))) (if ((TYPE_UNSIGNED (type) diff --git a/gcc/testsuite/gcc.dg/pr66552.c b/gcc/testsuite/gcc.dg/pr66552.c new file mode 100644 index 0000000..7583c9a --- /dev/null +++ b/gcc/testsuite/gcc.dg/pr66552.c @@ -0,0 +1,14 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -fdump-tree-lower" } */ + +unsigned a(unsigned x, int n) +{ + return x >> (n % 32); +} + +unsigned b(unsigned x, int n) +{ + return x << (n % 32); +} + +/* { dg-final { scan-tree-dump-not " % " "lower" } } */ |