[llvm] [ConstantFolding]Fold llvm.powi via square-and-multiply (PR #210771)

[Alexey Bataev via llvm-commits]

alexey-bataev wrote:

compiler-rt/lib/builtins/powisf2.c (and others), flang-rt runtime (FPow4i/FPow8i/FPow4k/FPow8k), flang const folding (flang/lib/Evaluate/int-power.h), SelectionDAGBuilder all use the same scheme. libgcc __powi{sf,df,tf,xf}2 , compiler-rt mirrors it.

Already have a related issue https://github.com/llvm/llvm-project/issues/65088



https://github.com/llvm/llvm-project/pull/210771