[SimplifyLibCalls] Add dereferenceable bytes from known callsites

Summary:
int mm(char *a, char *b) {
    return memcmp(a,b,16);
}

Currently:
define dso_local i32 @mm(i8* nocapture readonly %a, i8* nocapture readonly %b) local_unnamed_addr #1 {
entry:
  %call = tail call i32 @memcmp(i8* %a, i8* %b, i64 16)
  ret i32 %call
}

After patch:
define dso_local i32 @mm(i8* nocapture readonly %a, i8* nocapture readonly %b) local_unnamed_addr #1 {
entry:
  %call = tail call i32 @memcmp(i8* dereferenceable(16)  %a, i8* dereferenceable(16)  %b, i64 16)
  ret i32 %call
}




Reviewers: jdoerfert, efriedma

Reviewed By: jdoerfert

Subscribers: javed.absar, spatel, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D66079

llvm-svn: 368657