[llvm-bugs] [Bug 44147] New: Non-deterministic debug info with LTO

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=44147

            Bug ID: 44147
           Summary: Non-deterministic debug info with LTO
           Product: new-bugs
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: mh+llvm at glandium.org
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org

Created attachment 22867
  --> https://bugs.llvm.org/attachment.cgi?id=22867&action=edit
testcase archive

Steps to reproduce:
- Download and extract attachment
- Run the following command:
```
clang -m32 -pthread -g -O3 -shared -Wl,-z,defs -Wl,--gc-sections
-Wl,-h,libmozavutil.so -o libmozavutil.so avstring.o bprint.o buffer.o
channel_layout.o cpu.o crc.o dict.o error.o eval.o fifo.o fixed_dsp.o
float_dsp.o frame.o hwcontext.o imgutils.o log.o log2_tab.o mathematics.o mem.o
opt.o parseutils.o pixdesc.o rational.o reverse.o samplefmt.o slicethread.o
time.o utils.o -flto=thin -Wl,-plugin-opt=-import-instr-limit=10 -lpthread
-Wl,-z,noexecstack -Wl,-z,text -Wl,-z,relro -Wl,-z,nocopyreloc
-Wl,-Bsymbolic-functions -Wl,--build-id=sha1
-Wl,--version-script,libmozavutil.so.symbols -ldl -lrt -lm -latomic
```
- Save the generated libmozavutil.so
- Repeat enough times.

This is reproducible with BFD ld, gold, and lld. I've got 4 different variants
of the generated library so far with thousands of attempts. Frequency is 94.3%
for the most frequent variant, 2~3% each for two other ones, and 0.1% for the
last one.

This is also reproducible with current trunk (initially hit with clang 9 ; the
object files from the testcase were compiled with clang 9).

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