[llvm-bugs] [Bug 43526] New: Miscompilation after r355962: [SROA] Fix a crash when trying to convert a memset to an non-integral pointer

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=43526

            Bug ID: 43526
           Summary: Miscompilation after r355962: [SROA] Fix a crash when
                    trying to convert a memset to an non-integral pointer
           Product: new-bugs
           Version: unspecified
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: dmajor at mozilla.com
                CC: htmldeveloper at gmail.com, listmail at philipreames.com,
                    llvm-bugs at lists.llvm.org
            Blocks: 43360

Created attachment 22613
  --> https://bugs.llvm.org/attachment.cgi?id=22613&action=edit
Miscompilation analysis

After moving Firefox builds to clang 9.0.0, some of our tests failed because of
a miscompilation that began in r355962 according to a bisect.

Unfortunately I don't have a small repro and I'm not sure it's feasible to
produce one. The affected code is part of a huge binary that is built with LTO
and PGO, and we only see the issue on a single platform (Android ARM32) that is
difficult to build and debug locally.

I'm attaching a file containing a colleague's analysis of the generated code
near the point of failure (from
https://bugzilla.mozilla.org/show_bug.cgi?id=1583907#c17). A value that we
needed was placed into r0, but then r0 was immediately overwritten by something
else.

@reames, is there any chance you might be able to have a look at the analysis
and intuit what went wrong? I'm not sure what other hope we have of debugging
this.


Referenced Bugs:

https://bugs.llvm.org/show_bug.cgi?id=43360
[Bug 43360] [meta] 9.0.1 Release Blockers
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