linux-kernel - RE: [PATCH 02/10][v6] powerpc/Power7: detect load/store instructions

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Date:	Wed, 16 Oct 2013 09:25:35 +0100
From:	"David Laight" <David.Laight@...LAB.COM>
To:	"Sukadev Bhattiprolu" <sukadev@...ux.vnet.ibm.com>,
	"Arnaldo Carvalho de Melo" <acme@...stprotocols.net>
Cc:	"Michael Ellerman" <michaele@....ibm.com>,
	<linux-kernel@...r.kernel.org>,
	"Stephane Eranian" <eranian@...gle.com>, <linuxppc-dev@...abs.org>,
	"Paul Mackerras" <paulus@...ba.org>,
	"Anshuman Khandual" <khandual@...ux.vnet.ibm.com>
Subject: RE: [PATCH 02/10][v6] powerpc/Power7: detect load/store instructions

> Implement instr_is_load_store_2_06() to detect whether a given instruction
> is one of the fixed-point or floating-point load/store instructions in the
> POWER Instruction Set Architecture v2.06.
...
> +int instr_is_load_store_2_06(const unsigned int *instr)
> +{
> +	unsigned int op, upper, lower;
> +
> +	op = instr_opcode(*instr);
> +
> +	if ((op >= 32 && op <= 58) || (op == 61 || op == 62))
> +		return true;
> +
> +	if (op != 31)
> +		return false;
> +
> +	upper = op >> 5;
> +	lower = op & 0x1f;
> +
> +	/* Short circuit as many misses as we can */
> +	if (lower < 3 || lower > 23)
> +		return false;
> +
> +	if (lower == 3) {
> +		if (upper >= 16)
> +			return true;
> +
> +		return false;
> +	}
> +
> +	if (lower == 7 || lower == 12)
> +		return true;
> +
> +	if (lower >= 20) /* && lower <= 23 (implicit) */
> +		return true;
> +
> +	return false;
> +}

I can't help feeling the code could do with some comments about
which actual instructions are selected where.

	David



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