[InstCombine] Fold out-of-range bits for squaring signed integers (#153484)

Fixes an issue where bits next to the sign bit were not constant-folded
when squaring a sign- or zero-extended small integer. Added logic to
detect when both operands of a multiplication are the same extended
value, allowing InstCombine to mark bits above the maximum possible
square as known zero. This enables correct folding of (x * x) & (1 << N)
to 0 when N is out of range.

Proof: https://alive2.llvm.org/ce/z/YGou44

Fixes #152061

0 files changed, 0 insertions, 0 deletions