[llvm-bugs] [Bug 42254] New: @llvm.memcpy not honoring volatile

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=42254

            Bug ID: 42254
           Summary: @llvm.memcpy not honoring volatile
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Common Code Generator Code
          Assignee: unassignedbugs at nondot.org
          Reporter: gchatelet at google.com
                CC: llvm-bugs at lists.llvm.org

Full discussion here:
http://lists.llvm.org/pipermail/llvm-dev/2019-June/132808.html


The following IR with the volatile parameter set to true
> call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 1 %0, i8* align 1 %1, i64
7, i1 true)

generates the following asm:
> movl    (%rsi), %eax
> movl    3(%rsi), %ecx
> movl    %ecx, 3(%rdi)
> movl    %eax, (%rdi)

It performs an overlapping read/write which - I believe - is violating the
volatile semantic
Full example here: https://godbolt.org/z/P_rjBT

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