[Bug tree-optimization/114872] [13/14/15 Regression] Miscompilation with -O2 after commit r13-8037

["dima.pasechnik at cs dot ox.ac.uk" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114872

Dmitrii Pasechnik <dima.pasechnik at cs dot ox.ac.uk> changed:

           What    |Removed                     |Added
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                 CC|                            |dima.pasechnik at cs dot ox.ac.uk

--- Comment #12 from Dmitrii Pasechnik <dima.pasechnik at cs dot ox.ac.uk> ---
A colleague disassembled, using ghidra (https://ghidra-sre.org/), the results
of the compilations with, respectively, -O2 and with -O0 flags.
Comparing the results, in the broken (built with -O2) case one sees a
miscompilation of a call to GAP_CallFunc3Args - it is called with one argument
less than it should, three instead of four!

broken (-O2):

>               plVar9 = (long *)GAP_CallFunc3Args(*(undefined8 *)(param_1 + 0x20),local_a0[4],
>                                                  local_a8[4]);

vs. good (-O0):

< LAB_0013cbd9:
<             plVar10 = (long *)GAP_CallFunc3Args(*(undefined8 *)(param_1 +
0x20),local_a8[4],
<                                                 local_a0[4],plVar16[4]);

And this is despite the prototype for calling GAP_CallFunc3Args() is
found in "gap/libgap-api.h", which is included in example.c as #include
"gap/libgap-api.h",  meant to be respected during the compilation. 

I hope this helps in chasing down the obvious compiler bug. Perhaps it can be
also seen without disassembling, simply on the intermediate data generated by
the compiler.