[KnownBits] Add test for computing more information for lshr/ashr with exact flag; NFC

Author: goldsteinn

llvm/test/Analysis/ValueTracking/knownbits-shift.ll

@@ -0,0 +1,24 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -passes=instcombine -S < %s | FileCheck %s
+
+define i8 @simplify_lshr_with_exact(i8 %x) {
+; CHECK-LABEL: @simplify_lshr_with_exact(
+; CHECK-NEXT:    [[SHR:%.*]] = lshr exact i8 6, [[X:%.*]]
+; CHECK-NEXT:    [[R:%.*]] = and i8 [[SHR]], 2
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %shr = lshr exact i8 6, %x
+  %r = and i8 %shr, 2
+  ret i8 %r
+}
+
+define i8 @simplify_ashr_with_exact(i8 %x) {
+; CHECK-LABEL: @simplify_ashr_with_exact(
+; CHECK-NEXT:    [[SHR:%.*]] = ashr exact i8 -122, [[X:%.*]]
+; CHECK-NEXT:    [[R:%.*]] = and i8 [[SHR]], 2
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %shr = ashr exact i8 -122, %x
+  %r = and i8 %shr, 2
+  ret i8 %r
+}