[PATCH] ira: Don't substitute into TRAP_IF insns (PR78610)

[Jeff Law]

On 11/30/2016 05:46 AM, Segher Boessenkool wrote:
> In the testcase, IRA propagates a constant into a TRAP_IF insn, which
> then becomes an unconditional trap.  Unconditional traps are control
> flow insns so doing this requires surgery on the cfg.  We cannot do
> that here, so instead refuse to do the substitution.
>
> Bootstrapping + regression testing on powerpc64-linux {-m64,-m32}
> (the bug happened here with -m32); okay for trunk if this succeeds?
>
>
> Segher
>
>
> 2016-11-30  Segher Boessenkool  <segher@kernel.crashing.org>
>
> 	PR rtl-optimization/78610
> 	* ira.c (combine_and_move_insns): Don't substitute into TRAP_IF
> 	instructions.
>
> gcc/testsuite/
> 	PR rtl-optimization/78610
> 	* gcc.c-torture/compile/pr78610.c: New testcase.
Funny how you speculated there could be these issues hiding in the 
weeds, then just a few days later, one crawls out.

OK.  I do wonder if we're going to need a better mechanism for this in 
the long term, but OK for now.

jeff