[llvm-dev] analysis based on nonnull attribute

Sanjay Patel via llvm-dev llvm-dev at lists.llvm.org
Wed Dec 14 13:47:03 PST 2016

Does the nonnull parameter attribute give us information about subsequent
uses of that value outside of the function that has the attribute?


define i1 @bar(i32* nonnull %x) { ; %x must be non-null in this function
  %y = load i32, i32* %x
  %z = icmp ugt i32 %y, 23
  ret i1 %z

define i1 @foo(i32* %x) {
  %d = call i1 @bar(i32* %x)
  %null_check = icmp eq i32* %x, null ; check if null after call that
guarantees non-null?
  br i1 %null_check, label %t, label %f
  ret i1 1
  ret i1 %d

$ opt  -inline  nonnull.ll -S
define i1 @foo(i32* %x) {
  %y.i = load i32, i32* %x   ; inlined and non-null knowledge is lost?
  %z.i = icmp ugt i32 %y.i, 23
  %null_check = icmp eq i32* %x, null
  br i1 %null_check, label %t, label %f

  ret i1 true

  ret i1 %z.i
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