diff options
| author | Jakub Jelinek <jakub@redhat.com> | 2020-05-08 09:33:55 +0200 |
|---|---|---|
| committer | Jakub Jelinek <jakub@redhat.com> | 2020-05-08 09:33:55 +0200 |
| commit | df569f7da567af4996821dc0a1871eec79957d04 (patch) | |
| tree | cc4ced8f3fc3149413fca20171fb9bedf899abed /gcc/match.pd | |
| parent | ff33680165346cb291667f38dd2e9f25a74cc3c3 (diff) | |
match.pd: Optimize ffs of known non-zero arg into ctz + 1 [PR94956]
The ffs expanders on several targets (x86, ia64, aarch64 at least)
emit a conditional move or similar code to handle the case when the
argument is 0, which makes the code longer.
If we know from VRP that the argument will not be zero, we can (if the
target has also an ctz expander) just use ctz which is undefined at zero
and thus the expander doesn't need to deal with that.
2020-05-08 Jakub Jelinek <jakub@redhat.com>
PR tree-optimization/94956
* match.pd (FFS): Optimize __builtin_ffs* of non-zero argument into
__builtin_ctz* + 1 if direct IFN_CTZ is supported.
* gcc.target/i386/pr94956.c: New test.
Diffstat (limited to 'gcc/match.pd')
| -rw-r--r-- | gcc/match.pd | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/gcc/match.pd b/gcc/match.pd index cfe96975d80..892df1ec3d3 100644 --- a/gcc/match.pd +++ b/gcc/match.pd @@ -5986,6 +5986,16 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT) && direct_internal_fn_supported_p (IFN_POPCOUNT, type, OPTIMIZE_FOR_BOTH)) (convert (IFN_POPCOUNT:type @0))))) + +/* __builtin_ffs needs to deal on many targets with the possible zero + argument. If we know the argument is always non-zero, __builtin_ctz + 1 + should lead to better code. */ +(simplify + (FFS tree_expr_nonzero_p@0) + (if (INTEGRAL_TYPE_P (TREE_TYPE (@0)) + && direct_internal_fn_supported_p (IFN_CTZ, TREE_TYPE (@0), + OPTIMIZE_FOR_SPEED)) + (plus (CTZ:type @0) { build_one_cst (type); }))) #endif /* Simplify: |