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Re: [PATCH, rs6000] PR71800, use correct constraint for stxsiwx


Hi Pat,

On Thu, Jul 07, 2016 at 03:42:55PM -0500, Pat Haugen wrote:
> The following patch corrects the constraint so that we only generate 'stxsiwx' on Power8 or later hardware. Ok for trunk after successful bootstrap/regtest?

I don't really understand this.  Before, it required UPPER_REGS_DF (which
seems correct), and now it requires UPPER_REGS_SF, which seems wrong.

Could you explain a bit more please?


Segher


> 2016-07-07  Pat Haugen  <pthaugen@us.ibm.com>
> 
> 	PR target/71800
> 	* config/rs6000/rs6000.md (stfiwx): Change constraint to 'wu' to 
> 	prevent generation of 'stxsiwx' on pre Power8 hardware.
> 
> 
> Index: config/rs6000/rs6000.md
> ===================================================================
> --- config/rs6000/rs6000.md     (revision 238117)
> +++ config/rs6000/rs6000.md     (working copy)
> @@ -5748,7 +5748,7 @@ (define_expand "lround<mode>di2"
>  ; An UNSPEC is used so we don't have to support SImode in FP registers.
>  (define_insn "stfiwx"
>    [(set (match_operand:SI 0 "memory_operand" "=Z,Z")
> -	(unspec:SI [(match_operand:DI 1 "gpc_reg_operand" "d,wv")]
> +	(unspec:SI [(match_operand:DI 1 "gpc_reg_operand" "d,wu")]
> 		   UNSPEC_STFIWX))]
>    "TARGET_PPC_GFXOPT"
>    "@


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