[Bug rtl-optimization/113660] New: ICE: verify_flow_info failed: missing REG_EH_REGION note at the end of bb 2 with -fnon-call-exceptions -fharden-control-flow-redundancy on invalid

[Bug rtl-optimization/113660] New: ICE: verify_flow_info failed: missing REG_EH_REGION note at the end of bb 2 with -fnon-call-exceptions -fharden-control-flow-redundancy on invalid

[zsojka at seznam dot cz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113660

            Bug ID: 113660
           Summary: ICE: verify_flow_info failed: missing REG_EH_REGION
                    note at the end of bb 2 with -fnon-call-exceptions
                    -fharden-control-flow-redundancy on invalid
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Keywords: ice-on-invalid-code
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zsojka at seznam dot cz
  Target Milestone: ---
              Host: x86_64-pc-linux-gnu
            Target: x86_64-pc-linux-gnu

Created attachment 57254
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=57254&action=edit
reduced testcase

Compiler output:
$ x86_64-pc-linux-gnu-gcc -fnon-call-exceptions
-fharden-control-flow-redundancy testcase.c
testcase.c: In function 'foo':
testcase.c:5:3: error: impossible constraint in 'asm'
    5 |   __asm__ volatile("" : "=a"(i));
      |   ^~~~~~~
testcase.c:6:1: error: missing REG_EH_REGION note at the end of bb 2
    6 | }
      | ^
during RTL pass: into_cfglayout
testcase.c:6:1: internal compiler error: verify_flow_info failed
0xf904ae verify_flow_info()
        /repo/gcc-trunk/gcc/cfghooks.cc:287
0x268381b checking_verify_flow_info()
        /repo/gcc-trunk/gcc/cfghooks.h:214
0x268381b try_optimize_cfg
        /repo/gcc-trunk/gcc/cfgcleanup.cc:2980
0x268381b cleanup_cfg(int)
        /repo/gcc-trunk/gcc/cfgcleanup.cc:3143
0xfaaf8a execute
        /repo/gcc-trunk/gcc/cfgrtl.cc:3713
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.

$ x86_64-pc-linux-gnu-gcc -v
Using built-in specs.
COLLECT_GCC=/repo/gcc-trunk/binary-latest-amd64/bin/x86_64-pc-linux-gnu-gcc
COLLECT_LTO_WRAPPER=/repo/gcc-trunk/binary-trunk-r14-8487-20240129102032-gb338fdbc2b7-checking-yes-rtl-df-extra-nobootstrap-amd64/bin/../libexec/gcc/x86_64-pc-linux-gnu/14.0.1/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /repo/gcc-trunk//configure --enable-languages=c,c++
--enable-valgrind-annotations --disable-nls --enable-checking=yes,rtl,df,extra
--disable-bootstrap --with-cloog --with-ppl --with-isl
--build=x86_64-pc-linux-gnu --host=x86_64-pc-linux-gnu
--target=x86_64-pc-linux-gnu --with-ld=/usr/bin/x86_64-pc-linux-gnu-ld
--with-as=/usr/bin/x86_64-pc-linux-gnu-as --disable-libstdcxx-pch
--prefix=/repo/gcc-trunk//binary-trunk-r14-8487-20240129102032-gb338fdbc2b7-checking-yes-rtl-df-extra-nobootstrap-amd64
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 14.0.1 20240129 (experimental) (GCC)

[Bug rtl-optimization/113660] ICE: verify_flow_info failed: missing REG_EH_REGION note at the end of bb 2 with -fnon-call-exceptions -fharden-control-flow-redundancy on invalid

[aoliva at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113660

--- Comment #1 from Alexandre Oliva <aoliva at gcc dot gnu.org> ---
There's nothing specific about -fharden-control-flow-redundancy here, FWIW. 
ISTM that it just adds enough EH-related stuff to the function that an EH note
gets attached to the impossible asm, a stmt then insn at the end of a block. 
Then, when vregs realizes that the asm has impossible constraints, it deletes
it, and that loses the REG_EH_REGION note attached to it, which triggers the
error.  I'm not sure what the correct behavior would be, but presumably the
note would have to be preserved/moved, or not required.