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| author | Jakub Jelinek <jakub@redhat.com> | 2025-01-09 08:30:12 +0100 |
|---|---|---|
| committer | Jakub Jelinek <jakub@gcc.gnu.org> | 2025-01-09 08:30:12 +0100 |
| commit | 2cbd4409bcfaba2bd4200412090fd06db1948369 (patch) | |
| tree | f82deebf61348a86dd5ceb72e29485f7b2f1b8f8 /gcc/tree-pass.h | |
| parent | c5e71d22d632889860ef079d4b0bff21eef8a660 (diff) | |
| download | gcc-2cbd4409bcfaba2bd4200412090fd06db1948369.zip gcc-2cbd4409bcfaba2bd4200412090fd06db1948369.tar.gz gcc-2cbd4409bcfaba2bd4200412090fd06db1948369.tar.bz2 | |
match.pd: Avoid introducing UB in the a r<< (32-b) -> a r>> b optimization [PR117927]
As mentioned in the PR, the a r<< (bitsize-b) to a r>> b and similar
match.pd optimization which has been introduced in GCC 15 can introduce
UB which wasn't there before, in particular if b is equal at runtime
to bitsize, then a r<< 0 is turned into a r>> bitsize.
The following patch fixes it by optimizing it early only if VRP
tells us the count isn't equal to the bitsize, and late into
a r>> (b & (bitsize - 1)) if bitsize is power of two and the subtraction
has single use, on various targets the masking then goes away because
its rotate instructions do masking already. The latter can't be
done too early though, because then the expr_not_equal_to case is
basically useless and we introduce the masking always and can't find out
anymore that there was originally no masking. Even cfun->after_inlining
check would be too early, there is forwprop before vrp, so the patch
introduces a new PROP for the start of the last forwprop pass.
2025-01-09 Jakub Jelinek <jakub@redhat.com>
Andrew Pinski <quic_apinski@quicinc.com>
PR tree-optimization/117927
* tree-pass.h (PROP_last_full_fold): Define.
* passes.def: Add last= parameters to pass_forwprop.
* tree-ssa-forwprop.cc (pass_forwprop): Add last_p non-static
data member and initialize it in the ctor.
(pass_forwprop::set_pass_param): New method.
(pass_forwprop::execute): Set PROP_last_full_fold in curr_properties
at the start if last_p.
* match.pd (a rrotate (32-b) -> a lrotate b): Only optimize either
if @2 is known not to be equal to prec or if during/after last
forwprop the subtraction has single use and prec is power of two; in
that case transform it into orotate by masked count.
* gcc.dg/tree-ssa/pr117927.c: New test.
Diffstat (limited to 'gcc/tree-pass.h')
| -rw-r--r-- | gcc/tree-pass.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/gcc/tree-pass.h b/gcc/tree-pass.h index e764dc9..d46a6b1 100644 --- a/gcc/tree-pass.h +++ b/gcc/tree-pass.h @@ -230,6 +230,7 @@ protected: #define PROP_assumptions_done (1 << 19) /* Assume function kept around. */ #define PROP_gimple_lbitint (1 << 20) /* lowered large _BitInt */ +#define PROP_last_full_fold (1 << 21) /* Start of last forwprop. */ #define PROP_gimple \ (PROP_gimple_any | PROP_gimple_lcf | PROP_gimple_leh | PROP_gimple_lomp) |