[Bug c++/88630] New: Incorrect float negating together with convertion to int on SH4

[zavadovsky.yan at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88630

            Bug ID: 88630
           Summary: Incorrect float negating together with convertion to
                    int on SH4
           Product: gcc
           Version: 8.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zavadovsky.yan at gmail dot com
  Target Milestone: ---

Created attachment 45299
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=45299&action=edit
main.cpp: code to trigger the bug

Hello.

I have some strange behavior with such simple code:
<code>
float float_val = ....;
int int_val = -float_val;
</code>

Problem is in "losing" negation.
Real result of code execution looks like
<code>
int int_val = float_val;
</code>

E.g. if float_val==12.0f I am awaiting that int_val will be equal -12;
And vice versa.

But I got int_val==12 when float_val==12.0f;
I.e. there was no negation.


There is no such bug in GCC-4.x (checked 4.7.3 and 4.9.4).
It begins since 5.x(I checked 5.4.0, 6.3.0, 7.4.0, 8.2.0).

There is no such bug on x86-64, mips and arm with 4.6/4.7 and 6.3.0 compiler
versions.


Assembler from GCC-8.2.0 - works bad:
<code>
        sts     fpscr,r1
        mov.l   .L2,r2
        fneg    fr5
        xor     r2,r1
        lds     r1,fpscr
        ftrc    fr5,fpul
        sts     fpul,r0
        xor     r2,r1
        lds     r1,fpscr
        rts     
</code>


Assembler from GCC-4.9.4 - works good:
<code>
        mov.l   .L2,r1
        lds.l   @r1+,fpscr
        add     #-4,r1
        fneg    fr5
        add     #4,r1
        ftrc    fr5,fpul
        sts     fpul,r0
        rts     
        lds.l   @r1+,fpscr
</code>

I can see that FPU 'calculation' commands wasn't changed between compiler
versions.
But there was change of work with FPU status/control register.


Can somebody say is it compiler bug or there is a problem with my code?