[Bug target/103274] New: Remaining -freorder-blocks-and-partition/ glitch with Windows SEH

["tomas.kalibera at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103274

            Bug ID: 103274
           Summary: Remaining -freorder-blocks-and-partition/ glitch with
                    Windows SEH
           Product: gcc
           Version: 10.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tomas.kalibera at gmail dot com
  Target Milestone: ---

Created attachment 51809
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=51809&action=edit
When compiled with -O3, dummy ends in a call (invalid unwind information).

-freorder-blocks-and-partition sometimes causes a function to end right in a
(non-returning) call, but SEH needs at least one more instruction on x86_64.
Seen in GCC 10.3, 11.2 and git master. Maybe [1] did not cover all the cases?

The attached compile-only example compiled with -O3 reproduces the problem. It
is extracted from R, where this problem causes crashes (and where in wine, one
gets an error "virtual_unwind exception data not found" and further
instrumentation reveals it is because the address following the call
instruction is already at the function boundary). The problem can be seen
directly from the assembly:

gcc -O3 -c -S ../main/a.c -o -

produces

dummy:
 [...]
.L5:
        call    myerrorcall
        .seh_endproc
 [...]
dummy.cold:

For reference, R is affected by this and has been disabling SEH as a
workaround, but it has been reported that the workaround causes in turns
crashes with CFG.

This report is with substantial help from Martin Storsjo.

=======

[1]
https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=15278fb2877184c75a6ee3a6def09efbb191968b;hp=9d3b9a3e70e634c7c48bb12bb35ec8219024f98b

[2]
https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/config/i386/i386.c;h=1bca5a7eea6ab9accbbf6953f79e8a4da61859e2;hb=4212a6a3e44f870412d9025eeb323fd4f50a61da#l29076

[3]
https://github.com/llvm/llvm-project/blob/main/llvm/lib/Target/X86/X86AvoidTrailingCall.cpp

[4] https://bugs.r-project.org/show_bug.cgi?id=18180