Commit Graph

3 Commits

Author SHA1 Message Date
Sanjay Patel c0339c77ef [InstCombine] Fold nuw left-shifts in `ugt`/`ule` comparisons.
This transforms

%a = shl nuw %x, c1
%b = icmp {ugt|ule} %a, c0

into

%b = icmp {ugt|ule} %x, (c0 >> c1)

z3:

(declare-const x (_ BitVec 64))
(declare-const c0 (_ BitVec 64))
(declare-const c1 (_ BitVec 64))

(push)
(assert (= x (bvlshr (bvshl x c1) c1)))  ; nuw
(assert (not (= (bvugt (bvshl x c1) c0)
                (bvugt x
                       (bvlshr c0 c1)))))
(check-sat)
(get-model)
(pop)

(push)
(assert (= x (bvlshr (bvshl x c1) c1)))  ; nuw
(assert (not (= (bvule (bvshl x c1) c0)
                (bvule x
                       (bvlshr c0 c1)))))
(check-sat)
(get-model)
(pop)

Patch by bryant!

Differential Revision: https://reviews.llvm.org/D25913

llvm-svn: 285729
2016-11-01 19:19:29 +00:00
Sanjay Patel f3dda13bd2 [InstCombine] Ensure that truncated int types are legal.
Fixes the FIXMEs in D25952 and rL285075.

Patch by bryant!

Differential Revision: https://reviews.llvm.org/D25955

llvm-svn: 285108
2016-10-25 20:11:47 +00:00
Sanjay Patel 8f9235dd7f [InstCombine] add tests for missing icmp + shl nuw fold
Patch by bryant!

Differential Revision: https://reviews.llvm.org/D25952

llvm-svn: 285095
2016-10-25 18:47:56 +00:00