[Bug c/106609] New: [SH] miscompilation of loop involving noreturn call

["sebastien.michelland@ens-lyon.fr" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106609

            Bug ID: 106609
           Summary: [SH] miscompilation of loop involving noreturn call
           Product: gcc
           Version: 12.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sebastien.michelland@ens-lyon.fr
  Target Milestone: ---

Created attachment 53452
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53452&action=edit
Minimal test case

GCC 12.1.0 generates incorrect code for loops that call into noreturn functions
starting at -O1. For example,

__attribute__((noreturn)) void g(void);
void f(int *values)
{
    for(int i = 0; i < 8; i++)
        if(values[i] != 0) g();
}

gets compiled into

        sts.l   pr,@-r15
        mov     #8,r1
.L3:    bt.s    .L2
        dt      r1
        mov.l   .L5,r1 # _g
        jsr     @r1
        nop
.L2:    bf      .L3
        lds.l   @r15+,pr
        rts     
        nop

which has the obvious issue of not reading its input, and also using the T bit
through bt.s before doing any test.

I suppose this is an overly aggressive loop/CFG optimization, but I was not
able to trim it down as unfolding -O1 into the list of optimizations provided
by -Q --help=optimizers produced a completely different program. The bug still
occurs with -fno-aggressive-loop-optimizations at least.

With -funroll-all-loops, instead of 8 mov.l/tst/bf I just get 8 bf which
suggests that the test is wrongly eliminated causing the load to become dead.

Found in:
  GCC 12.1.0
  Commit 4991e2092 of today's master
Not found in:
  GCC 11.1.0
Configured with:
  ../gcc-12.1.0/configure --prefix=$PREFIX --target=sh3eb-elf
--enable-languages=c --without-headers
Reproduction instructions:
  $PREFIX/bin/sh3eb-elf-gcc -S noreturn-loop-bug.c -o - -O1