llvm-project

e8af134b - [InstCombine] Generalize trunc-shift-icmp fold from (1 << Y) to (Pow2 << Y) (#169163)

[InstCombine] Generalize trunc-shift-icmp fold from (1 << Y) to (Pow2 << Y) (#169163) Extends the `icmp(trunc(shl))` fold to handle any power of 2 constant as the shift base, not just 1. This generalizes the following patterns by adjusting the comparison offsets by `log2(Pow2)`. ```llvm (trunc (1 << Y) to iN) == 0 --> Y u>= N (trunc (1 << Y) to iN) != 0 --> Y u< N (trunc (1 << Y) to iN) == 2**C --> Y == C (trunc (1 << Y) to iN) != 2**C --> Y != C ; to (trunc (Pow2 << Y) to iN) == 0 --> Y u>= N - log2(Pow2) (trunc (Pow2 << Y) to iN) != 0 --> Y u< N - log2(Pow2) (trunc (Pow2 << Y) to iN) == 2**C --> Y == C - log2(Pow2) (trunc (Pow2 << Y) to iN) != 2**C --> Y != C - log2(Pow2) ``` Proof: https://alive2.llvm.org/ce/z/2zwTkp