; ModuleID = '/tmp/test.c'
source_filename = "/tmp/test.c"
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"


%struct.Arg = type { i8, i64 }


define noundef i64 @evalexpr_broken(ptr %0) {
entry:
  %isnullp = getelementptr %struct.Arg, ptr %0, i32 0
  %arg0p = getelementptr %struct.Arg, ptr %0, i32 1

  ; value that's needed just temporarily, during "operation" below
  store i8 38, ptr %isnullp

  %arg0 = load i64, ptr %arg0p

  ; operation that has been optimized out would be here, elided for brevity

  %isnull = load i8, ptr %isnullp

  ; signal that memory at %isnullp isn't needed anymore
  store i8 poison, ptr %isnullp

  ret i64 %arg0
}


define noundef i64 @evalexpr_works(ptr %0) {
entry:
  %isnullp = getelementptr %struct.Arg, ptr %0, i32 0
  %arg0p = getelementptr %struct.Arg, ptr %0, i32 1

  store i8 38, ptr %isnullp

  %arg0 = load i64, ptr %arg0p

  %isnull = load i8, ptr %isnullp
  store i8 poison, ptr %isnullp

  ; now that the return value isn't needed anymore, optimizer can optimize away
  ; the store to %isnullp
  ret i64 0
}