gnu /
gcc /
7dae3f64c069b942b9abd768fd94af4b2cd0b781 match.pd: Fold ((X >> C1) & C2) * (1 << C1)
Using a combination of rules, we were able to fold
((X >> C1) & C2) * (1 << C1) --> X & (C2 << C1)
if everything was done at the same precision, but we couldn't fold
it if the AND was done at a different precision. The optimisation is
often (but not always) valid for that case too.
This patch adds a dedicated rule for the case where different precisions
are involved.
An alternative would be to extend the individual folds that together
handle the same-precision case so that those rules handle differing
precisions. But the risk is that that could replace narrow operations
with wide operations, which would be especially harmful on targets
like avr. It's also not obviously free of cycles.
I also wondered whether the converts should be non-optional.
gcc/
* match.pd: Fold ((X >> C1) & C2) * (1 << C1) to X & (C2 << C1).
gcc/testsuite/
* gcc.dg/fold-mul-and-lshift-1.c: New test.
* gcc.dg/fold-mul-and-lshift-2.c: Likewise.
3 files changed
