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| author | Roger Sayle <roger@nextmovesoftware.com> | 2024-07-27 15:16:19 +0100 |
|---|---|---|
| committer | Thomas Koenig <tkoenig@gcc.gnu.org> | 2024-07-28 19:06:02 +0200 |
| commit | 262163238006aa39eff5ebd8283ec7254161269a (patch) | |
| tree | 0d0e29afb765a51703d9922d8343d53f0fe62349 /gcc | |
| parent | f3ed8cd8f72240a31d6591f0156ea7d3258b1736 (diff) | |
| download | gcc-262163238006aa39eff5ebd8283ec7254161269a.zip gcc-262163238006aa39eff5ebd8283ec7254161269a.tar.gz gcc-262163238006aa39eff5ebd8283ec7254161269a.tar.bz2 | |
Fold ctz(-x) and ctz(abs(x)) as ctz(x) in match.pd.
The subject line pretty much says it all; the count-trailing-zeros function
of -X and abs(X) produce the same result as count-trailing-zeros of X.
This transformation eliminates a negation which may potentially overflow
with an equivalent expression that doesn't [much like the analogous
abs(-X) simplification in match.pd].
I'd noticed this -X equivalence, which isn't mentioned in Hacker's Delight,
investigating whether ranger's non_zero_bits can help determine whether
an integer variable may be converted to a floating point type exactly
(without raising FE_INEXACT), but it turns out this observation isn't
novel, as (disappointingly) LLVM already performs this same folding.
2024-07-27 Roger Sayle <roger@nextmovesoftware.com>
Andrew Pinski <quic_apinski@quicinc.com>
gcc/ChangeLog
* match.pd (ctz (-X) => ctz (X)): New simplification.
(ctz (abs (X)) => ctz (X)): Likewise.
gcc/testsuite/ChangeLog
* gcc.dg/fold-ctz-1.c: New test case.
* gcc.dg/fold-ctz-2.c: Likewise.
Diffstat (limited to 'gcc')
| -rw-r--r-- | gcc/match.pd | 6 | ||||
| -rw-r--r-- | gcc/testsuite/gcc.dg/fold-ctz-1.c | 9 | ||||
| -rw-r--r-- | gcc/testsuite/gcc.dg/fold-ctz-2.c | 9 |
3 files changed, 24 insertions, 0 deletions
diff --git a/gcc/match.pd b/gcc/match.pd index b2e7d61..1c86012 100644 --- a/gcc/match.pd +++ b/gcc/match.pd @@ -9102,6 +9102,12 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT) /* CTZ simplifications. */ (for ctz (CTZ) + /* ctz (-X) => ctz (X). ctz (abs (X)) => ctz (X). */ + (for op (negate abs) + (simplify + (ctz (nop_convert?@0 (op @1))) + (with { tree t = TREE_TYPE (@0); } + (ctz (convert:t @1))))) (for op (ge gt le lt) cmp (eq eq ne ne) (simplify diff --git a/gcc/testsuite/gcc.dg/fold-ctz-1.c b/gcc/testsuite/gcc.dg/fold-ctz-1.c new file mode 100644 index 0000000..dcc444c --- /dev/null +++ b/gcc/testsuite/gcc.dg/fold-ctz-1.c @@ -0,0 +1,9 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -fdump-tree-optimized" } */ + +int foo(int x) +{ + return __builtin_ctz (-x); +} + +/* { dg-final { scan-tree-dump-not "-x_" "optimized"} } */ diff --git a/gcc/testsuite/gcc.dg/fold-ctz-2.c b/gcc/testsuite/gcc.dg/fold-ctz-2.c new file mode 100644 index 0000000..c685698 --- /dev/null +++ b/gcc/testsuite/gcc.dg/fold-ctz-2.c @@ -0,0 +1,9 @@ +/* { dg-do compile } */ +/* { dg-options "-O2 -fdump-tree-optimized" } */ + +int foo(int x) +{ + return __builtin_ctz (__builtin_abs (x)); +} + +/* { dg-final { scan-tree-dump-not "ABS_EXPR" "optimized"} } */ |