[Bug tree-optimization/112385] `(2 >> a) ^ (5 >> a)` is not optimized to `7 >> a` is 2 and 5 differ in signedness
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112385 Andrew Pinski changed: What|Removed |Added Ever confirmed|0 |1 Last reconfirmed||2023-11-12 Status|UNCONFIRMED |ASSIGNED Assignee|unassigned at gcc dot gnu.org |pinskia at gcc dot gnu.org --- Comment #3 from Andrew Pinski --- Mine, I will handle this.
[Bug tree-optimization/112385] `(2 >> a) ^ (5 >> a)` is not optimized to `7 >> a` is 2 and 5 differ in signedness
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112385 --- Comment #2 from Andrew Pinski --- We can even do it if we know the unsigned value does not have the last bit set. That is: ``` int f(int a, unsigned b, int c) { b &= 0x; return (c >> a) ^ (b >> a); } ``` Note clang(LLVM) does not handle the above. The way LLVM handles the others is it changes ashift to lshift if the value is known to be non-negative. But since in the gimple level we are dealing with types we can't do that in a nice way; RTL level on the other hand yes that can be done (though nonzero bits is limited there).
[Bug tree-optimization/112385] `(2 >> a) ^ (5 >> a)` is not optimized to `7 >> a` is 2 and 5 differ in signedness
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112385 --- Comment #1 from Andrew Pinski --- Note a more complex case like: ``` int f(int a, unsigned b, int c) { c &= 0x; return (c >> a) ^ (b >> a); } ``` Should also be optimized to: ``` int f(int a, unsigned b, int c) { c &= 0x; return (c^b) >> a; } ``` That is if both are known to be non-negative we can do the combining.