[llvm-bugs] [Bug 39119] New: Null check elimination when callsite args are nonnull

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=39119

            Bug ID: 39119
           Summary: Null check elimination when callsite args are nonnull
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: david.bolvansky at gmail.com
                CC: llvm-bugs at lists.llvm.org

int foo(char *d, char *s) {
    int res = strncmp(d, s, 10);
    if (!s)
        abort();
    return res;
}

Current -O3 IR:
define dso_local i32 @foo(i8* nocapture readonly %d, i8* readonly %s)
local_unnamed_addr #0 {
entry:
  %tobool = icmp eq i8* %s, null
  br i1 %tobool, label %if.then, label %if.end

if.then:                                          ; preds = %entry
  tail call void @abort() #3
  unreachable

if.end:                                           ; preds = %entry
  %call = tail call i32 @strncmp(i8* %d, i8* nonnull %s, i64 10) #4
  ret i32 %call
}

We somehow miss logic to remove "top level null check", if all uses of %s are
in "nonnull" places

---------------------------------------------

For similar code:
int foo(char *d, char *s) {
    int res = strncmp(d, s, 10);
    if (!s)
        abort();
    if (!d)
        exit(1);
    return res;
}

We get:
define dso_local i32 @foo(i8* readonly %d, i8* readonly %s) local_unnamed_addr
#0 {
entry:
  %call = tail call i32 @strncmp(i8* %d, i8* %s, i64 10) #3
  %tobool = icmp eq i8* %s, null
  br i1 %tobool, label %if.then, label %if.end

if.then:                                          ; preds = %entry
  tail call void @abort() #4
  unreachable

if.end:                                           ; preds = %entry
  %tobool1 = icmp eq i8* %d, null
  br i1 %tobool1, label %if.then2, label %if.end3

if.then2:                                         ; preds = %if.end
  tail call void @exit(i32 1) #4
  unreachable

if.end3:                                          ; preds = %if.end
  ret i32 %call
}

But if I change
%call = tail call i32 @strncmp(i8* %d, i8* %s, i64 10) #3
to 
%call = tail call i32 @strncmp(i8* nonnull %d, i8* nonnull %s, i64 10) #3

Ran:
opt -O3 -enable-nonnull-arg-prop aa.ll -S

No eliminations :/ We need to propagate nonnull info more.

-- 
You are receiving this mail because:
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-bugs/attachments/20180928/b84bac66/attachment.html>