[Bug tree-optimization/92712] [8/9 Regression] Performance regression with assumed values
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92712 --- Comment #25 from Marc Glisse --- (In reply to Feng Xue from comment #24) > Another point: if B+-C can be folded to an existing gimple value, we might > deduce B+-C does not overflow? We can deduce that loading this value that represents B+-C does not overflow at runtime (since we aren't computing anything, just copying some other value), but not that the operation B+-C would not overflow if it was actually evaluated. So it could help a bit sometimes. We still need to ensure that the multiplication by A does not overflow though.
[Bug tree-optimization/92712] [8/9 Regression] Performance regression with assumed values
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92712 Feng Xue changed: What|Removed |Added CC||fxue at os dot amperecomputing.com --- Comment #24 from Feng Xue --- If(In reply to Jakub Jelinek from comment #15) > For > A*B+A*C -> (B+C)*A > the problematic cases are > A==-1 and B > 0 and C==(max-B)+1 (i.e. when B+C overflows to min) > or A==0 and B < 0 and C or A==0 and B > 0 and C>max-B > (last two cases cover when B+C overflows) > For > A*B-A*C -> (B-C)*A > the problematic cases are > A==-1 and B > 0 and C==min+B (i.e. when B-C is min) > or A==0 and B < -1 and C>B-min > or A==0 and B >= 0 and C (last two cases cover when B-C overflows) > Again, we perform the operation right now if A is not 0 and not -1 for > certain. > I guess we could handle those cases by using something like > check_for_binary_op_overflow, except that for the case where A might be -1 > and plusminus equal to MINUS_EXPR we also need to make sure the result of > B-C is known not to be min. Another point: if B+-C can be folded to an existing gimple value, we might deduce B+-C does not overflow?
[Bug tree-optimization/92712] [8/9 Regression] Performance regression with assumed values
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92712 Jakub Jelinek changed: What|Removed |Added Target Milestone|8.4 |8.5 --- Comment #23 from Jakub Jelinek --- GCC 8.4.0 has been released, adjusting target milestone.
[Bug tree-optimization/92712] [8/9 Regression] Performance regression with assumed values
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92712 Jakub Jelinek changed: What|Removed |Added Summary|[8/9/10 Regression] |[8/9 Regression] |Performance regression with |Performance regression with |assumed values |assumed values --- Comment #22 from Jakub Jelinek --- Should be fixed on the trunk. I don't think we want to backport to release branches though.
