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Re: [PATCH][AArch64] Mark symbols as constant


On 19/06/17 19:59, Wilco Dijkstra wrote:
> Aarch64_legitimate_constant_p currently returns false for symbols,
> eventhough they are always valid constants.  This means LOSYM isn't
> CSEd correctly.  If we return true CSE works better, resulting in
> smaller/faster code (0.3% smaller code on SPEC2006).
> 
> int x0 = 1, x1 = 2, x2 = 3;
> 
> int 
> f (int x, int y)
> {
>   x += x1;
>   if (x > 100)
>     y += x2;
>   x += x0;
>   return x + y;
> }
> 
> Before:
> 	adrp	x3, .LANCHOR0
> 	add	x4, x3, :lo12:.LANCHOR0
> 	ldr	w2, [x3, #:lo12:.LANCHOR0]
> 	add	w0, w0, w2
> 	cmp	w0, 100
> 	ble	.L5
> 	ldr	w2, [x4, 8]
> 	add	w1, w1, w2
> .L5:
> 	add	x3, x3, :lo12:.LANCHOR0
> 	ldr	w2, [x3, 4]
> 	add	w0, w0, w2
> 	add	w0, w0, w1
> 	ret
> 
> After:
> 	adrp	x2, .LANCHOR0
> 	add	x3, x2, :lo12:.LANCHOR0
> 	ldr	w2, [x2, #:lo12:.LANCHOR0]
> 	add	w0, w0, w2
> 	cmp	w0, 100
> 	ble	.L5
> 	ldr	w2, [x3, 8]
> 	add	w1, w1, w2
> .L5:
> 	ldr	w2, [x3, 4]
> 	add	w0, w0, w2
> 	add	w0, w0, w1
> 	ret
> 
> Passes regress and bootstrap, OK for commit?
> 
> ChangeLog:
> 2017-06-19  Wilco Dijkstra  <wdijkstr@arm.com>
> 
> 	* config/aarch64/aarch64.c (aarch64_legitimate_constant_p):
> 	Return true for symbols.
> --
> diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
> index 5ec6bbfcf484baa4005b8a88cb98d0d04f710877..4b7d961102e41ce927d89d458fc89ddfc2adcd6f 100644
> --- a/gcc/config/aarch64/aarch64.c
> +++ b/gcc/config/aarch64/aarch64.c
> @@ -10111,6 +10111,9 @@ aarch64_legitimate_constant_p (machine_mode mode, rtx x)
>        && aarch64_valid_symref (XEXP (x, 0), GET_MODE (XEXP (x, 0))))
>      return true;
>  
> +  if (SYMBOL_REF_P (x))
> +    return true;
> +
>    return aarch64_constant_address_p (x);
>  }
>  
> 

What testing has this had with -fpic?  I'm not convinced that this
assertion is true in that case?

R.


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