[llvm-bugs] [Bug 39962] New: MS ABI incompatibility when calling virtual function with single bool parameter

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=39962

            Bug ID: 39962
           Summary: MS ABI incompatibility when calling virtual function
                    with single bool parameter
           Product: clang
           Version: 6.0
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM Codegen
          Assignee: unassignedclangbugs at nondot.org
          Reporter: cerickson at curedev.com
                CC: llvm-bugs at lists.llvm.org, neeilans at live.com,
                    richard-llvm at metafoo.co.uk

Created attachment 21213
  --> https://bugs.llvm.org/attachment.cgi?id=21213&action=edit
Repro case showing the incorrect behavior

When calling a clang-compiled virtual function from an msvc-compiled function,
the virtual function's single bool parameter is passed incorrectly (an argument
of `false` becomes `true`).

This only happens when optimizations are applied to the msvc-compiled source
file (starting with /O1).

This bug appears in the wild when passing a std::function by value across a
compiler boundary, as in this case here: 

https://stackoverflow.com/questions/50388773/stdfunction-clang-6-0-msvc-10-0017134-12-possible-abi-bug-or-required-c

std::function ends up performing a double delete as a result of misinterpreting
a bool argument in this fashion.


I've attached a repro case that can be run on an X64 Windows machine with VS
2017 installed.

The expected output of the test case:

[msc] Calling EnsureFalse(false)
[clang] Inside EnsureFalse(false)

The actual output:

[msc] Calling EnsureFalse(false)
[clang] Inside EnsureFalse(true)

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