Re: [PATCH] genemit: Handle `const_double_zero' rtx

[Jeff Law <law@redhat.com>]

On 12/15/20 1:38 PM, Maciej W. Rozycki wrote:
> Complement commit 20ab43b5cad6 ("RTL: Add `const_double_zero' syntactic 
> rtx") and remove a commit c60d0736dff7 ("PDP11: Use `const_double_zero' 
> to express double zero constant") build regression observed with the 
> `pdp11-aout' target:
>
> genemit: Internal error: abort in gen_exp, at genemit.c:202
> make[2]: *** [Makefile:2427: s-emit] Error 1
>
> where a:
>
> (const_double 0 [0] 0 [0] 0 [0] 0 [0])
>
> rtx coming from:
>
> (parallel [
>         (set (reg:CC 16)
>             (compare:CC (abs:DF (match_operand:DF 1 ("general_operand") ("0,0")))
>                 (const_double 0 [0] 0 [0] 0 [0] 0 [0])))
>         (set (match_operand:DF 0 ("nonimmediate_operand") ("=fR,Q"))
>             (abs:DF (match_dup 1)))
>     ])
>
> and ultimately `(const_double_zero)' referred in a named RTL insn cannot 
> be interpreted.  Handle the rtx then by supplying the constant 0 double 
> operand requested, resulting in the following update to insn-emit.c code 
> produced for the `pdp11-aout' target, relative to before the triggering 
> commit:
>
> @@ -1514,7 +1514,7 @@ gen_absdf2_cc (rtx operand0 ATTRIBUTE_UN
>  	gen_rtx_COMPARE (CCmode,
>  	gen_rtx_ABS (DFmode,
>  	operand1),
> -	const0_rtx)),
> +	CONST_DOUBLE_ATOF ("0", VOIDmode))),
>  		gen_rtx_SET (operand0,
>  	gen_rtx_ABS (DFmode,
>  	copy_rtx (operand1)))));
> @@ -1555,7 +1555,7 @@ gen_negdf2_cc (rtx operand0 ATTRIBUTE_UN
>  	gen_rtx_COMPARE (CCmode,
>  	gen_rtx_NEG (DFmode,
>  	operand1),
> -	const0_rtx)),
> +	CONST_DOUBLE_ATOF ("0", VOIDmode))),
>  		gen_rtx_SET (operand0,
>  	gen_rtx_NEG (DFmode,
>  	copy_rtx (operand1)))));
> @@ -1790,7 +1790,7 @@ gen_muldf3_cc (rtx operand0 ATTRIBUTE_UN
>  	gen_rtx_MULT (DFmode,
>  	operand1,
>  	operand2),
> -	const0_rtx)),
> +	CONST_DOUBLE_ATOF ("0", VOIDmode))),
>  		gen_rtx_SET (operand0,
>  	gen_rtx_MULT (DFmode,
>  	copy_rtx (operand1),
> @@ -1942,7 +1942,7 @@ gen_divdf3_cc (rtx operand0 ATTRIBUTE_UN
>  	gen_rtx_DIV (DFmode,
>  	operand1,
>  	operand2),
> -	const0_rtx)),
> +	CONST_DOUBLE_ATOF ("0", VOIDmode))),
>  		gen_rtx_SET (operand0,
>  	gen_rtx_DIV (DFmode,
>  	copy_rtx (operand1),
>
> 	gcc/
> 	* genemit.c (gen_exp) <CONST_DOUBLE>: Handle `const_double_zero' 
> 	rtx.
> ---
> Hi,
>
>  I have verified this with a bootstrap of a `powerpc64le-linux-gnu' native 
> compiler, and that it builds a `pdp11-aout' cross-compiler up to the point 
> of failing to find target headers.  I have no means to verify it further, 
> the target configuration is too exotic to me, so I will appreciate help.
>
>  NB this only triggers with insn-emit.c code produced from named RTL insns 
> for the purpose of calling them directly, which does not apply for the VAX 
> backend, as it does not give names to any insns using `const_double_zero'.  
> Which is why I didn't spot this issue with all my VAX verification.
>
>  Thanks to Martin for bringing my attention to this regression, and sorry 
> to miss this in testing.
>
>  OK to apply?
Presumably you can't use CONST0_RTX (mode) here?  Assuming that's the
case, then this is fine.

jeff