[Bug target/70439] New: Incorrect DRAP check in ix86_expand_epilogue

["hjl.tools at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70439

            Bug ID: 70439
           Summary: Incorrect DRAP check in ix86_expand_epilogue
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hjl.tools at gmail dot com
                CC: ubizjak at gmail dot com
  Target Milestone: ---
            Target: x86

ix86_expand_epilogue has

    /* eh_return epilogues need %ecx added to the stack pointer.  */
      if (style == 2)
        {   
          rtx sa = EH_RETURN_STACKADJ_RTX;
          rtx_insn *insn;

          /* Stack align doesn't work with eh_return.  */
          gcc_assert (!stack_realign_drap);
          /* Neither does regparm nested functions.  */
          gcc_assert (!ix86_static_chain_on_stack);

EH_RETURN_STACKADJ_RTX is defined to %ecx, which conflicts with DRAP
which also uses %ecx.  When stack_realign_drap is true, ix86_get_drap_rtx
emits DRAP register. But ix86_finalize_stack_realign_flags may set
crtl->stack_realign_needed to false later.  When we get ix86_expand_epilogue,
stack_realign_drap is false, but DRAP is actually used, which leads to wrong
code.