[llvm-bugs] [Bug 37970] New: clang non-deterministic DEBUG_VALUE output, armv7a-linux-androideabi -mthumb -O2 -g

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https://bugs.llvm.org/show_bug.cgi?id=37970

            Bug ID: 37970
           Summary: clang non-deterministic DEBUG_VALUE output,
                    armv7a-linux-androideabi -mthumb -O2 -g
           Product: libraries
           Version: trunk
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: ARM
          Assignee: unassignedbugs at nondot.org
          Reporter: chh at google.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 20485
  --> https://bugs.llvm.org/attachment.cgi?id=20485&action=edit
output 1.s and 2.s have different @DEBUG_VALUE sequences

To reproduce, modify and run the run.sh script in the test.zip.
Repeated compilations of the same input file produced different @DEBUG_VALUE
sequences in 1.s and 2.s.

The problem occurred with -target armv7a-linux-androideabi -mthumb -O2 -g.
Other targets, -O1, or -g1 seemed to produce deterministic output.

I traced back to llvm change https://reviews.llvm.org/rL321862,
which started to have such problem. I am not sure if that change
is buggy or just exposed an older bug.

The test case was reduced from Android open source code.
It is required in Android release process to be able to generate identical
output from the same input and compiler. We cannot release Android without a
fix or reversing rL321862.

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