[llvm-bugs] [Bug 52441] New: Debug info makes build results non-deterministic

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=52441

            Bug ID: 52441
           Summary: Debug info makes build results non-deterministic
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Common Code Generator Code
          Assignee: unassignedbugs at nondot.org
          Reporter: ilya.yanok at gmail.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 25430
  --> https://bugs.llvm.org/attachment.cgi?id=25430&action=edit
Input that triggers the bug

This was found by Rust here: https://github.com/rust-lang/rust/issues/90301

I was able to extract an LLVM example (see attached).

One can test it with

$ llc -O0 input.ll

Running it several times (usually 10 is enough) you will get slightly different
results.

I've bisected it to commit 1db137b1859692ae33228c530d4df9f2431b2151
Author: Stephen Tozer <Stephen.Tozer at Sony.com>
Date:   Wed Mar 10 14:25:09 2021 +0000

    [DebugInfo] Handle DBG_VALUES with multiple variable location operands in
MIR

    This patch adds handling for DBG_VALUE_LIST in the MIR-passes (after
    finalize-isel), excluding the debug liveness passes and DWARF emission.
This
    most significantly affects MachineSink, which now needs to consider all
used
    registers of a debug value when sinking, but for most passes this change is
    simply replacing getDebugOperand(0) with an iteration over all debug
operands.

    Differential Revision: https://reviews.llvm.org/D92578

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