[llvm-bugs] [Bug 31993] New: clang generating memcpy with source/destination overlap

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=31993

            Bug ID: 31993
           Summary: clang generating memcpy with source/destination
                    overlap
           Product: new-bugs
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: mikael.holmen at ericsson.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 18001
  --> https://bugs.llvm.org/attachment.cgi?id=18001&action=edit
reproducer

With
clang -S -emit-llvm tr13026.c -o tr13026.ll

we get this memcpy call in the output

  call void @llvm.memcpy.p0i8.p0i8.i64(i8* bitcast (%struct.anon* @s to i8*),
i8* bitcast (%struct.anon* @s to i8*), i64 4, i32 4, i1 false)

where the dest and source arguments are the same, and thus clearly overlap.

However, in the documentation:
http://llvm.org/docs/LangRef.html#llvm-memcpy-intrinsic

it says:
"The ‘llvm.memcpy.*‘ intrinsics copy a block of memory from the source location
to the destination location, which are not allowed to overlap."

And if running lint on the output:
opt -S -lint -o tr13026.opt.ll tr13026.ll

we get a warning about it:

Undefined behavior: memcpy source and destination overlap
  call void @llvm.memcpy.p0i8.p0i8.i64(i8* bitcast (%struct.anon* @s to i8*),
i8* bitcast (%struct.anon* @s to i8*), i64 4, i32 4, i1 false)

-- 
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/20170217/2461b3e7/attachment.html>