[Bug c/112494] New: GCC: 14: internal compiler error: in ix86_cc_mode, at config/i386/i386.cc:16477

["141242068 at smail dot nju.edu.cn" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112494

            Bug ID: 112494
           Summary: GCC: 14: internal compiler error: in ix86_cc_mode, at
                    config/i386/i386.cc:16477
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: 141242068 at smail dot nju.edu.cn
  Target Milestone: ---

Compiler Explorer: https://gcc.godbolt.org/z/cPPxenx7q

When compile this program with `-Og  -fno-tree-copy-prop -fno-tree-fre
-fno-tree-ccp -fno-tree-forwprop`, gcc crashes:
```
#include <x86intrin.h>

#ifdef __x86_64__
#  define EFLAGS_TYPE unsigned long long int
#else
#  define EFLAGS_TYPE unsigned int
#endif

int main() {
  EFLAGS_TYPE flags = 0xD7;
  __writeeflags(0xD7);
  flags && !__readeflags();
  if ((flags && (!__readeflags())) != 0xD7);
  return 0;
}
```

There are some intriguing observations about this crash.
1. Removing the `flags &&` portion at the point of the first __readeflags()
call eliminates the crash, even though it appears that `flags &&` has no
effect.
2. Removing the `!= 0xD7` portion at the point of the second __readeflags()
call also eliminates the crash.


The crash output:
```
during RTL pass: combine
<source>: In function 'main':
<source>:15:1: internal compiler error: in ix86_cc_mode, at
config/i386/i386.cc:16477
   15 | }
      | ^
0x238b15e internal_error(char const*, ...)
        ???:0
0xa11270 fancy_abort(char const*, int, char const*)
        ???:0
Please submit a full bug report, with preprocessed source (by using
-freport-bug).
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.
Compiler returned: 1
```