[llvm-bugs] [Bug 40657] IR programs printing incorrect results after being compiled with -O0

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=40657

Sanjay Patel <spatel+llvm at rotateright.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|CONFIRMED                   |RESOLVED
 Fixed By Commit(s)|                            |r353615, r353639
         Resolution|---                         |FIXED

--- Comment #10 from Sanjay Patel <spatel+llvm at rotateright.com> ---
All attached examples should be fixed after:
https://reviews.llvm.org/rL353639

Feel free to reopen if that's not correct.

Side note about fuzzing for LLVM bugs:
If you're looking for backend bugs, it might be worth trying something like
this:

$ clang -O2 test.c -S -emit-llvm -Xclang -disable-llvm-optzns -o
unoptimized_ir.ll
$ llc -O2 unoptimized_ir.ll -o unoptimized_ir_optimized_asm.s
$ clang unoptimized_ir_optimized_asm.s -o maybe_buggy_executable
$ clang test.c -o reference_executable
$ { compare output of } reference_executable maybe_buggy_executable

A lot of people get that 1st step wrong: you want clang to create an IR file
that allows optimization by the backend, but skip intermediate optimization.
That doesn't happen if you use "-O0 -emit-llvm" with clang.

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