[llvm] [AArch64] Use isKnownNonZero to optimize eligible compares to cmn (PR #96349)

[David Green via llvm-commits]

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@@ -258,3 +258,34 @@ define i32 @neg_range_int(i32 %a, i32 %b, i32 %c) {
   ret i32 %retval.0
 }
 
+; (b > -3 || a < -(c | 1))
+define i32 @neg_range_int_cmn(i32 %a, i32 %b, i32 %c) {
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davemgreen wrote:

In the new code in this test:
```
define i32 @or_neg(i32 %x, i32 %y) {
; CHECK-LABEL: or_neg:
; CHECK:       // %bb.0:
; CHECK-NEXT:    orr w8, w0, #0x1
; CHECK-NEXT:    cmn w8, w1
; CHECK-NEXT:    cset w0, gt
; CHECK-NEXT:    ret
  %3 = or i32 %x, 1
  %4 = sub i32 0, %3
  %5 = icmp sgt i32 %4, %y
  %6 = zext i1 %5 to i32
  ret i32 %6
}
```
If, say, x==0, y==0 then is the result not backwards?

https://github.com/llvm/llvm-project/pull/96349