[llvm-branch-commits] [GIselValueTracking] Correctly truncate/zext G_PTRTOADDR (PR #143816)

[Alexander Richardson via llvm-branch-commits]

https://github.com/arichardson created https://github.com/llvm/llvm-project/pull/143816

G_PTRTOADDR is defined to return a zero-extended pointer address, so in
case of ptr addrspace(8) 48 bits follwed by zeroes. Fixes the
PtrToAddrExt test case in knownbits-ptrtoaddr.mir.