[ValueTracking] Return true for AddrSpaceCast in canCreateUndefOrPoison (#144686)
In our downstream GPU target, following IR is valid before instcombine
although the second addrspacecast causes UB.
define i1 @test(ptr addrspace(1) noundef %v) {
%0 = addrspacecast ptr addrspace(1) %v to ptr addrspace(4)
%1 = call i32 @llvm.xxxx.isaddr.shared(ptr addrspace(4) %0)
%2 = icmp eq i32 %1, 0
%3 = addrspacecast ptr addrspace(4) %0 to ptr addrspace(3)
%4 = select i1 %2, ptr addrspace(3) null, ptr addrspace(3) %3
%5 = icmp eq ptr addrspace(3) %4, null
ret i1 %5
}
We have a custom optimization that replaces invalid addrspacecast with
poison, and IR is still valid since `select` stops poison propagation.
However, instcombine pass optimizes `select` to `or`:
%0 = addrspacecast ptr addrspace(1) %v to ptr addrspace(4)
%1 = call i32 @llvm.xxxx.isaddr.shared(ptr addrspace(4) %0)
%2 = icmp eq i32 %1, 0
%3 = addrspacecast ptr addrspace(1) %v to ptr addrspace(3)
%4 = icmp eq ptr addrspace(3) %3, null
%5 = or i1 %2, %4
ret i1 %5
The transform is invalid for our target.
---------
Co-authored-by: Nikita Popov <github@npopov.com>
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