[PATCH] Fix wide-int multiplication (PR tree-optimization/65170)

[Richard Sandiford]

Jakub Jelinek <jakub@redhat.com> writes:
> Hi!
>
> To represent 128-bit unsigned multiplication results of 64-bit unsigned
> operands one sometimes needs 3 HWIs instead of 2.
>
> Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux,
> ok for trunk?
>
> 2015-02-23  Jakub Jelinek  <jakub@redhat.com>
>
> 	PR tree-optimization/65170
> 	* wide-int.cc (wi::mul_internal): For the umul_ppmm optimization,
> 	if val[1] < 0, clear also val[2] and return 3.
>
> 	* gcc.c-torture/execute/pr65170.c: New test.
> 	* gcc.dg/tree-ssa/vrp96.c: New test.
>
> --- gcc/wide-int.cc.jj	2015-01-27 09:25:38.000000000 +0100
> +++ gcc/wide-int.cc	2015-02-23 15:43:20.303280261 +0100
> @@ -1297,6 +1297,11 @@ wi::mul_internal (HOST_WIDE_INT *val, co
>  	      return 1;
>  	    }
>  	  umul_ppmm (val[1], val[0], op1.ulow (), op2.ulow ());
> +	  if (val[1] < 0)
> +	    {
> +	      val[2] = 0;
> +	      return 3;
> +	    }

Think this needs to check "prec > HOST_BITS_PER_WIDE_INT * 2",
otherwise val[2] isn't relevant and might not exist.

Lookd good to me with that change, thanks.

Richard