[InstCombine] Optimize icmp slt signum(x), 1 --> icmp slt x, 1
Summary:
`signum(x)` is sometimes implemented as `(x >> 63) | (-x >>> 63)` (for
an `i64` `x`). This change adds a matcher for that pattern, and an
instcombine rule to optimize `signum(x) s< 1`.
Later, we can also consider optimizing:
icmp slt signum(x), 0 --> icmp slt x, 0
icmp sle signum(x), 1 --> true
etc.
Reviewers: majnemer
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D12703
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@247846 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed